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Chapter 1 - Introduction -
 

 

Why Study Human Aging?                                  

 

Personal and Professional Reasons

 

Why have you chosen to study human aging? Why have others done so? For some people the answer is based on personal reasons. Younger individuals may expect to live long enough to reach old age and may wonder what will happen to them as they get older. They also may want to learn about aging so that they can improve their chances of aging happily and with good health. Curiosity or interest in bolstering oneís well-being may be a prime reason older individuals study aging. Still other individuals may have family members, friends, colleagues, or acquaintances who are experiencing aging. Their interest may spring from curiosity about what is happening to those other people. Beyond being curious, individuals may want to be better able to interact with and care for older people.

 

On a professional level, some individuals study human aging because their careers involve working with or caring for older people. The careers of others may entail carrying out research on or educating people about human aging.

 

Whatever your reasons for studying human aging, you should be aware that people have many reasons for doing so and that those who are studying human aging are being joined by a growing number of people.

 

Population Trends

 

(The data in this section are updated annually by the US Census Bureau and other agencies. Refer to the latest data and updates for Chapter 1)

 

 

Why has the study of aging become so important during the last few decades? One main reason is the rapid increase in the number of elderly people. According to current projections, this will continue until about A.D. 2030, after which the number of elderly people will rise more slowly (Fig. 1.1) (Fig. 1.1 HTML). The proportion of elderly persons in the total population is also rising and will probably continue to grow for several decades. For example, in 2000, 21.4 percent of the population was over age 54. This number should rise to about 29.7 percent by the year 2020, it will probably increase to about 32.6 percent by the year 2040, and grow to about 35.2 percent by 2060 (Table 1.1).

 

There will also be an increase in both the number and proportion of people of higher ages (Fig. 1.1 (Fig. 1.1 HTML)Fig. 1.2  Graph (Fig. 1.2 Graph HTML) and Fig. 1.2 Web Sites (Fig. 1.2 HTML)). For example, consider all people over age 65. In 2000, they numbered 34.8 million, made up 12.7 percent of the total population, and represented 59.2 percent of the population over age 55. By the year 2020 the corresponding statistics will probably change to 56.1 million, 16.9 percent, and 56.7 percent, respectively. By the year 2040 these values should reach 80.8 million, 21.6 and 66.3 percent, respectively. In 2020, those over age 84 will likely comprise 2.0 percent of the total population and 12.0 percent of people over age 64. By the year 2040, those over age 84 may make up 3.9 percent of the total population and 17.9 percent of people over age 64.

 

Four factors explain these population changes. One factor is the high birth rates before 1920 and between 1946 and 1964, followed by a decrease after 1964 (Fig. 1.3 (Fig. 1.3 HTML)). A second is the high number of births between 1946 and 1964 (Fig. 1.4  (Fig. 1.4 HTML)). A third factor is the decline in childhood death rates, especially during the first year of life (Fig. 1.5 (Fig. 1.5 HTML)). Since the childhood death rate in 1940 was already low compared with 1900 and since the childhood death rate dropped substantially between 1940 and 1955, a much higher percentage of those born during these latter years survived into adulthood. The last factor is the increase in life expectancy at all ages, including middle age and old age. (Fig. 1.6 (Fig. 1.6 HTML)) . Between 1900 and 1940, life expectancy for those over age 64 increased by less than one year, while it increased almost two years between 1940 and 1954. Life expectancy for those over age 64 increased more than 2.6 years since then. Because of these circumstances, a large group is now entering old age while a smaller group is replacing them as the younger segment of the population. This large group has become known as the "baby boomers" (Fig. 1.7 (Fig. 1.7 HTML)). Life expectancy for all adults including those over age 64 is expected to continue increasing for decades. Therefore, a larger percentage of those reaching old age will  remain alive longer. In terms of populations and elders, the "baby boomer bump" is the wave of the future. It should be noted that major changes in immigration since 2000 are likely to have significant effects on the number and percentages of elders in the US population. The US Census Bureau is taking these changes into consideration in making population projections.

 

The significance of these increases in the number and proportion of older people is that the elderly will have an ever greater influence on many aspects of society. As a group they will spend larger amounts of money, use more services, and have more political power. Therefore, an understanding of aging processes and other age-related changes is vital if society is to adapt to the changes that will accompany this phenomenon. Such an understanding may be especially important for those who, by virtue of their leadership positions, make decisions that have a broad impact, such as corporate and political decision makers.

 

What Is Aging?

 

Exactly what is aging? How would you define it? Do all people use the same definition? Is aging different from other changes that occur as people get older? The term aging is difficult to define because it has diverse meanings for different people. However, one definition will be selected here to help in the study of aging. To understand this definition, we must first understand developmental changes.

 

Developmental changes are irreversible normal changes in a living organism that occur as time passes. The same changes can be expected to occur in all members of a particular type of organism in a natural population (i.e., not genetically altered intentionally or living in a carefully controlled ďartificialĒ environment). Developmental changes are neither accidental nor a result of abuse, misuse, disuse, or disease. They occur in humans from the moment of conception to the moment of death. Familiar examples include growth in height, sexual maturation, and graying of the hair. The field of biology in which developmental changes are studied is called developmental biology.

 

Note that developmental changes are irreversible or at least rarely reversible. Conversely, bodily changes that occur in one direction for a while and then reverse direction are called physiological changes. Some physiological changes, such as increases and decreases in the rate of breathing, are rapidly reversible. Others, such as fluctuations in weight and physical fitness, are reversed more slowly.

 

Developmental changes can be divided into three categories. The first consists of changes that occur before birth or during childhood. Examples include the formation of specialized organs from a single-celled fertilized egg and increases in muscle coordination. Collectively, these early changes are usually called development. Studies of development before birth constitute the segment of biology called embryology.

 

The second category includes changes that result in the transformation of a child into an adult. These changes make up what is frequently called maturation. Puberty is an example of maturation. Both development and maturation consist of changes that usually improve the ability of a person to survive. Examples include the strengthening of muscles and bones and increases in intellectual ability.

 

The third category - aging refers to the group of developmental changes that become most evident in the later years; these are also called age changes. Examples described in later chapters include stiffening of the lungs, thinning of the bones, and a declining sense of smell. For practical purposes, the later years of life are considered in this book to begin about age 50. However, no one knows when many age changes that become evident in the later years actually start. Many age changes, such as reductions in kidney function, begin as early as age 20. Unlike development and maturation, almost all age changes reduce a personís ability to maintain healthy survival and a high quality of life. The term senescence includes only those age changes that have such detrimental effects. However, there are beneficial age changes, such as certain changes in the sweat glands, the heart, and the brain. These and other examples of positive age changes are described in Chaps. 3, 4, and 6.

 

Types of Aging

 

Biological Aging   Aging includes several different kinds of changes. One group of changes - biological aging - involves aging in the physical structures and functioning of the body that affects a personís ability to survive or a personís appearance. Biological aging is the main topic of this book. To understand its significance, one must first understand what is required for the survival and well-being of the body.

 

The human body, like most living things, is made up of small units called cells and materials that the cells produce. For example, muscles are made up mostly of muscle cells (Fig. 1.8a (Fig. 1.8a HTML)). By contrast, bones contain some bone cells but consist mostly of materials that those cells secrete (Fig. 1.8b (Fig. 1.8b HTML)).

 

The cells do more than furnish the substance of the body: They also perform all of its functions. Every thought and movement a person has actually results from nerve cells producing and carrying impulses and muscle cells moving. If the cells stopped working, there would be no bodily activity.

 

The cells of the body must have just the right set of conditions virtually all the time to build and maintain the structure of the body and carry out its functions. The state of having proper and fairly steady conditions is called homeostasis. It involves many conditions, such as temperature, nutrient levels, water content, and other parameters measured in medical checkups and diagnoses. Each condition may change slightly from time to time; such small changes occur because being alive means doing things such as growing and moving, and doing things causes changes in body conditions (Fig. 1.9 (Fig. 1.9 HTML)). For example, an ordinary activity such as walking raises body temperature, burns nutrients for energy, and results in water loss by evaporation from breathing and perspiring. Even the environment surrounding the body tends to cause changes within the body. An example is the tendency of body temperature to drop when a person is in a cool room because warm objects lose heat to a cool environment.

 

For a person to stay alive and well, each condition must not be allowed to stray above or below an acceptable range. If one of them, such as temperature, deviates too far, the cells will be injured and begin to malfunction. This means that the body is malfunctioning. Its well-being, and perhaps its very survival, is then jeopardized. The greater the number of injured cells and the more severe the injury, the greater the decline in bodily functioning and well-being and the greater the danger to the body.

 

If the errant condition is out of the acceptable range for only a brief period or to only a small degree, the cells can often recover once conditions are again favorable. However, if the deviation is present for an extended period, is extreme, or occurs frequently many times, some cells may be permanently altered or killed. The body has then lost the contributions which those cells should be making (Fig. 1.3 (Fig. 1.3 HTML)). Again, depending on the amount of injury, the result can range from barely noticeable discomfort to death.

 

Consider what happens to a person whose body temperature is dropping. As body temperature falls, the heart cells and brain cells slow down. If the chill is not severe or long-lasting, the person will recover completely once the body is warmed again. However, if the temperature drops too far or if the person stays chilled for a long time, as can happen when a person  falls into icy water, cell functioning becomes so slow that the person dies of hypothermia.

 

Since many activities are occurring inside the body and many changes occur -in its surroundings, one might ask how conditions for the cells are kept proper and fairly stable. Part of the answer involves the ability of the body to provide materials and structures that tend to prevent changes in these conditions. For example, fat under the skin helps prevent cooling by slowing heat loss from the body. The other part of the answer is the process of negative feedback, which involves three steps. The first step is detecting the presence of deviations from homeostasis. The next is informing the parts of the body that some condition is unacceptable and telling them how to slow, stop, or correct the developing problem. The nervous system contributes to these steps by continuously monitoring conditions such as body temperature. For example, if the nervous system detects a drop in temperature, it sends impulses to several parts of the body (Fig. 1.10 (Fig. 1.10 HTML)). The brain is informed about the problem, and the person is warned of the danger by the feeling of being cold. The skin and the muscles are directed to compensate for the developing deviation from homeostasis.

 

The third step in negative feedback is making the necessary adjustment to slow or stop the deviation before it causes a loss of homeostasis, or to restore the condition to a normal level. Many body systems contribute to this process. For example, when the body becomes chilled, the person may use muscles and bones to turn on a heater or move to a warmer location. The blood vessels in the skin become narrow. Both actions would reduce the loss of heat, slowing or stopping the deviation from progressing. The muscles may then cause shivering as they contract and relax quickly and repeatedly to produce more heat to warm the body, thus compensating for heat loss and returning the body to a normal internal temperature. These and other activities maintain and restore normal body temperature before any cells are significantly affected. Homeostasis is maintained and the cells stays alive and well.

 

A similar process that can help maintain homeostasis is positive feedback. This process also the same has three steps, except that the third step increases the change being made. To remain beneficial, the body provides a mechanism to stop the positive feedback system before it causes excess changes. Examples include inflammatory reactions when cells are injured or killed and immune reactions when the body detects foreign substances on or in the body. If an inflammatory or immune reaction is not stopped in time, the reaction becomes harmful (e.g., scar formation, allergic reaction). Other positive feedback systems that remain beneficial as long as they are stopped in time include blood clotting and impulse conduction by action potentials. (Chapters 3, 4 and 6) Harmful outcomes from these when unchecked include blood clots blocking vessels and seizures. Still other beneficial positive feedback systems include certain human sexual responses, ovulation, and uterine contractions during childbirth. (Chapters 13, 14, and 15)

 

Having developed an appreciation for how the body keeps itself alive and well, one can understand the importance of biological aging. With few exceptions, biological aging reduces the ability of the body to maintain homeostasis and therefore to survive. This happens in two main ways.

 

First, some biological age changes allow more rapid or extreme alterations in body conditions to occur. For example, thinning of the insulating layer of fat under the skin allows the body to chill faster.

 

Second, other biological age changes reduce the functioning of negative feedback systems and positive feedback systems. For negative feedback systems, there is a decline in the ability of certain parts of the body to detect alterations in body conditions and notify other parts that the body is threatened. Age changes in the nervous system are among the most important in this category. With aging, there is a decrease in the number of nerve cells that monitor conditions, and the nerve cells that remain often function weakly. Thus, the detection of deviations from homeostasis, such as a lowering of body temperature, is reduced. The ability to notify and activate parts of the body that can reduce, eliminate, or correct the problem also declines. This is especially pronounced when several parts of the body must act in a coordinated fashion. For example, there is a decline in coordinating the many complex muscle contractions needed to maintain balance while one is standing on a moving surface such as a boat deck. Finally, the structures that should restore conditions to an acceptable level are less able to do so. For example, as aging causes a decrease in the amount of muscle, there is a reduced ability to produce heat to raise body temperature back to normal.

 

Positive feedback systems also become weaker and less beneficial due to decreases in their detection, notification, activation, and control phases.

 

In summary, most biological aging allows more of the conditions in the body to stray further from the acceptable range and to stay beyond the normal range longer or more frequently. This causes more cells to be injured and fail in their functions. When many cells are affected to a large degree, the person feels less well and does not function as well. When to many cells are no longer able to perform adequately, the person becomes ill and dies.

 

Chronological Aging   The simplest type of aging is chronological aging, which refers to the passage of time since birth. It is usually measured in years, though sometimes decades are used. While chronological age can be useful in estimating the average status of a large group of people, it is a poor indicator of an individual personís status because there is tremendous variation among individuals in the rate biological age changes occur. For example, on the average, aging results in people losing much of their ability to perform strenuous activities, yet some elderly individuals are excellent marathon runners.

 

Cosmetic Aging   Cosmetic aging consists of changes in outward appearance with advancing age. This includes changes in the body and changes in other aspects of a personís appearance, such as the style of hair and clothing, the type of eyeglasses worn, and the use of a hearing aid. Like chronological aging, it is frequently used to estimate the degree to which other types of aging have occurred. It is even used to guess a personís chronological age. However, it is an inaccurate indicator for either purpose because of variation among individuals and because a personís appearance is affected by many factors that are not part of aging, including illness, poor nutrition, and exposure to sunlight.

 

Although cosmetic aging provides little evidence about other forms of aging, it can have profound effects on many aspects of life. For example, people who notice that their hair is turning gray may begin to think of themselves as old, and this may result in withdrawal from physically demanding activities, loss of appetite, depression, and subsequent declining health. Since people in this situation may lose interest in their appearance and may look worse because of ill health, they may be entering a vicious spiral of decline. The time, effort, and money that people spend trying to look young provides further evidence for the importance of appearance.

 

Social Aging   Another type of aging is social aging, which consists of age changes in the interactions people have with others. The birth of grandchildren, for example, can alter the ways in which the new parents interact with the new grandparents and even the ways in which the maternal and paternal grandparents relate to each other.

 

As with chronological and cosmetic aging, social aging has an impact on other age changes. The death of a spouse, for example, may decrease a personís interest in his or her own appearance, leading to cosmetic changes. The loneliness that often follows the loss of a spouse may cause stress, which in turn may result in a more rapid decline in the ability to fight off infection.

 

Psychological Aging   Psychological aging consists of age changes that affect the way people think and behave. It often results from other types of aging. For example, biological aging of the brain directly affects the speed of learning and the ability to remember some types of information. Examples involving other types of aging were mentioned above.

 

Psychological aging also contributes to other types of aging. Memory loss can result in forgetting to keep an appointment with a friend or a physician. Slowed thinking can prevent a person from retaining certain types of employment, such as jobs requiring rapid decision-making involving many variables (e.g., flight controller, fighter pilot, emergency room staff, crisis situation manager), especially in unfamiliar situations (e.g., newly employed or promoted).

 

Economic Aging   Economic aging consists of age changes in a personís financial status. Like psychological aging, economic aging can result from other types of aging. For example, in spite of laws against discrimination based on chronological age, some older people find it difficult to retain a job or obtain a new one simply because of their age. The resulting loss of income can cause difficulty in obtaining proper medical treatment or purchasing adequate food. Loss of contact with business colleagues and lowered self-esteem can have social and psychological effects.

 

Social Aging   Another type of aging is social aging, which consists of age changes in the interactions people have with others. The birth of grandchildren, for example, can alter the ways in which the new parents interact with the new grandparents and even the ways in which the maternal and paternal grandparents relate to each other.

 

As with chronological and cosmetic aging, social aging has an impact on other age changes. The death of a spouse, for example, may decrease a personís interest in his or her own appearance, leading to cosmetic changes. The loneliness that often follows the loss of a spouse may cause stress, which in turn may result in a more rapid decline in the ability to fight off infection.

 

Psychological Aging   Psychological aging consists of age changes that affect the way people think and behave. It often results from other types of aging. For example, biological aging of the brain directly affects the speed of learning and the ability to remember some types of information. Examples involving other types of aging were mentioned above.

 

Psychological aging also contributes to other types of aging. Memory loss can result in forgetting to keep an appointment with a friend or a physician. Slowed thinking can prevent a person from retaining certain types of employment, such as jobs requiring rapid decision-making involving many variables (e.g., flight controller, fighter pilot, emergency room staff, crisis situation manager), especially in unfamiliar situations (e.g., newly employed or promoted).

 

Economic Aging   Economic aging consists of age changes in a personís financial status. Like psychological aging, economic aging can result from other types of aging. For example, in spite of laws against discrimination based on chronological age, some older people find it difficult to retain a job or obtain a new one simply because of their age. The resulting loss of income can cause difficulty in obtaining proper medical treatment or purchasing adequate food. Loss of contact with business colleagues and lowered self-esteem can have social and psychological effects.

 

 

Spiritual Aging  Spiritual aging consists of age changes in a personís spirituality. This topic seems to be the most recent aspect of aging to be studied and discussed. Consequently, there is not yet a consensus on what happens during spiritual aging. Moreover, there is no consensus on the meaning and definition spirituality. To some people, spirituality is a personís religion, religious thinking and the outward expression thereof. To others, spirituality has nothing to do with religion. Still others view spirituality as a combination of religious and non-religious aspects of a person. Thus, spiritual aging includes age changes in a combination of beliefs, understandings, experiences, and awareness included in spirituality. (Table 1.1)

 

Table 1.1 Possible components of spirituality

 

Beliefs and understandings regarding;

      the existence of oneís soul (Soul), itís importance, and itís status

      a sense of well-being

      death, including oneís own and that of others

      essential motivations

      fundamental values and what are of essential importance

      hardship and suffering

      oneís interior mental thoughtful life

      oneís true essential nature Ė what constitutes oneís existence

      the essential purposes of living

      the fundamental principles that motivate and direct all other activities

      the value of survival

      what constitutes quality of life

      what is true happiness

      the essential purposes of living

      the fundamental principles that motivate and direct all other activities

      the value of survival

      core values

      guiding principles

      fundamental philosophy of existence

      non-material aspect of existence

      the existence and nature of the supernatural

      perspectives on the entire human race; past, present, and future

      relationships with other people and relationships among people

      a greater power that is outside of the oneís self

      oneís self, defined with regard to relationships to others

 

Experiences of;

      faith

      hope

      inner peace and calmness, or inner conflict and turmoil

      awe and transcendence

      internal inward-looking, which may include self evaluation

 

Awareness or sense of;

      values and thinking that guides oneís conduct

      relationships with a Creator, God (by any name), gods, and supernatural beings

      overall success and accomplishment in life

      purpose for existing and oneís life as a whole

      interconnectedness with all that exists

 

Interactions among Types of Aging   As is seen from the above examples, most types of aging can result from any of the other types. Also, each type can influence the others, and complex series of interactions can develop. The one exception is that chronological aging cannot be altered by the other types of aging (Fig. 1.11(Fig. 1.11 HTML)).

 

What Aging Is Not

 

It is important to note that many changes in the elderly are thought to be age changes but are abnormal rather than true age changes. Some abnormal changes result from abuse or misuse of parts of the body. Examples include skin wrinkling caused by sunlight (farmers), hearing loss caused by loud noise (factory workers), and joint stiffness caused by repeated traumatic injury (athletes). Other abnormal changes that are often thought to be age changes result from disuse. Examples include reductions in the pumping capacity of the heart, muscle power, and bone strength caused by inadequate exercise. Changes from extrinsic factors such as abuse, misuse, and disuse frequently accompany or amplify true age changes. For example, aging does cause some skin wrinkling, hearing loss, joint stiffness, muscle weakening, and bone weakening. Since many extrinsically caused abnormal changes in aging individuals are not severe enough to be considered disease, they are called ďusualĒ age changes by some authors. People who avoid these abnormal changes while undergoing normal age changes are said to have achieved ďsuccessfulĒ aging.

 

In addition to abnormal changes mentioned above, many abnormal changes that accompany aging are not part of true aging but are aspects of a disease. A person has a disease if that personís body has any one of three characteristics; (1) it has homeostasis but it cannot maintain homeostasis when it encounters a mild adverse condition that would not destroy homeostasis in most people (e.g., having diabetes where ingesting a small amount of sugar causes the blood sugar level to rise excessively, having AIDS where the immune system cannot kill certain types of cancer cells); (2) conditions in at least a part of the body are severe enough to be causing injury or death to cells there (e.g., having an infected finger, having a broken thigh bone); (3) conditions in many or all parts of the body are out of the acceptable range (e.g., having high blood pressure, having kidney failure.) A disease may be short term (acute), long term or recurring (chronic), in a small area (local), or widespread (systemic).

 

However, aging is not a disease, does not mean disease, and does not automatically include disease. The elderly are more susceptible than the young to certain diseases, but no diseases  

occur only in the elderly or occur in every elderly person.

 

Why then is aging often equated with disease? This probably stems from the much higher incidence of diseases among the elderly. One reason for this increase in disease is that most age changes reduce the ability of the body to keep conditions within the normal range. As examples, timing mechanisms may only delay diseases under genetic control, the sensory function of the nervous system declines, reflexes become slower and weaker, and immune responses against infection dwindle. However, there are compensating mechanisms that make up for many of these detrimental changes. Something as simple as wearing warmer clothing can compensate for the reduced ability to maintain an adequate body temperature. The use of eyeglasses and brighter lighting can restore much of the decline in vision. Allowing more time for tasks can make up for slower reactions and slower learning or remembering. Practicing and using experience can make accomplishing a task quick, easy and efficient. Avoiding exposure to infectious agents places less demand on defense mechanisms. If one creatively develops and uses compensating strategies, many undesirable consequences of aging that increase the likelihood of disease can be reduced or eliminated.

 

A second reason for the increase in disease with advancing age is that years must pass before some diseases become serious enough to be noticed. Sometimes this is because of the reserve capacity found in many parts of the body. Having reserve capacity means that under normal resting conditions, only a fraction of the full functional capacity of certain organs is needed to maintain homeostasis. For example, up to 50 percent of the functional capacity of the kidneys may be lost before a person notices that something is wrong. When body structures have little reserve capacity, a disease is not noticed because it progresses very slowly. For example, osteoarthritis, the most common type of arthritis, seems to require the cumulative effect of years of abuse of the joints before it becomes a problem. Also, atherosclerosis, which is a type of hardening of the arteries (arteriosclerosis), frequently begins before a heart attack because deterioration of the arteries occurs slowly, the heart attacks and strokes it causes usually do not occur until several decades later.

 

A third reason for the age-related increase in disease is that as time passes, there is a greater chance that a person will be subjected to factors that promote disease and that these exposures will occur many times and for longer periods. Examples include physical trauma, infectious organisms, air pollution, harmful radiation, and bad nutrition.

 

These facts indicate a very important point: Many abnormal changes associated with aging can be prevented, and the progress of many other diseases can be slowed enough so that their detrimental effects may be delayed for many years. It is even possible that their effects will not become apparent before death from other causes occurs. Of course, not all cases of every disease are preventable. Diseases such as Alzheimerís disease and rheumatoid arthritis cannot be prevented at all. However, for many age-related diseases, the use of disease prevention strategies before the disease begins often reduces the seriousness of its effects. For example, avoiding cigarette smoking reduces the effects of emphysema caused by other types of air pollution or by genetic factors.

 

Usually, all a person needs to do is avoid the factors that increase the risk of developing abnormal changes and the diseases that cause many of them. For risk factors, such as air pollution, that cannot be completely avoided, reducing their intensity or the frequency of exposure can help. This can reduce or nearly eliminate the chances of developing certain abnormal changes.

 

To be most effective, the avoidance of risk factors must begin early in life, but changing bad habits will probably help at any age. Even when a person begins to develop an abnormal change or disease, reducing risk factors can slow its progress so much that the change or disease may never become a significant problem. Some of the most important risk factors are smoking, stress, poor nutrition, inadequate exercise, and excessive exposure to harmful chemicals and sunlight. Others can be identified only by a medical checkup, including high blood pressure and high levels of cholesterol in the blood.

 

Finally, there is good news for those who develop a disease. Many diseases, including serious ones such as certain types of cancer and dementia, can be cured. Many others, such as arthritis, can be treated so that they have a minimal impact on a personís lifestyle. Early detection is important because it greatly increases the success achieved by treatment.

 

Why Study Biological Aging?

 

We have discussed several broad reasons for studying aging in general and biological aging in particular. We will now examine more specific reasons for studying biological aging. One of the most important is being able to distinguish true age changes from changes that occur by chance or are caused by abuse, misuse, disuse, or disease. Individuals with this ability will b changes in the body that represent the beginning of an abnormal condition. Then effective steps can be taken to prevent or combat undesirable changes that are not inevitable results of aging. Effort will not be wasted worrying about or attempting to alter conditions resulting from aging. Having knowledge about biological aging also makes it easier to select appropriate preventive or corrective measures. Furthermore, if one knows the course of age changes, the effects and effectiveness of new treatments can be better evaluated. There will be less chance of confusing the effects of a treatment with the effects of aging. Knowing the timing and nature of age changes also provides some predictability. Better estimates of a personís future biological or medical status can be made, and it is easier to predict the life expectancy of an individual or a group of people.

 

How is Biological Aging Studied?

 

Two methods are commonly used to study biological aging, and each has advantages and disadvantages. The most reliable conclusions regarding aging are those supported by both types of study or a combination of the two.

 

Cross-Sectional Method

 

A cross-sectional study starts with a group of people of different ages who are placed into age categories. In some cases, each category may contain all individuals who have reached the same age in years; in other cases, each category may contain all individuals whose age in years falls within a selected range. For example, each range may span five years. Thus, one category may include all those between the ages of 45 and 49; the next category may include all those between the ages of 50 and 54; and so on. Alternatively, the age ranges may be of different sizes, such as all those age 50 through 59 and all those age 60 and above.

 

Once the categories have been established, the researchers measure characteristics such as an intelligence, muscle strength, or heart rate for each individual. The data for individuals in each category are then compared with the data from individuals in the other categories. In this way, correlations between differences in characteristics and increases in age can be identified. If a trend is observed, the researchers conclude that it is caused by increasing age.

 

Cross-sectional studies are very popular for several reasons. First, they can be done quickly, and so there is no need to wait for years while the subjects in the study age. Second, since each subject needs to be evaluated only once, many subjects can be tested and then released from the study. Therefore, this procedure is relatively inexpensive. Third, since many subjects are included in the study, the results are statistically reliable. Finally, these studies largely eliminate the problem of a period effect. A period effect is the influence of events or conditions during the study on the people being studied. For example, changes in the employment status of the subjects during an economic depression or a war cause period effects.

 

There are several drawbacks to cross-sectional studies. A very important one is that such studies do not really measure changes that occur as time passes. It is only inferred that the differences among the age groups result from the passage of time. These differences could be caused by other factors that affected the subjects before the study. This flaw in the basic design of cross-sectional studies is called a birth-cohort effect. For example, the individuals in certain age categories might have been different from those in the other age categories at birth. This could have resulted from immigration or from relocation of large segments of the population. Thus, one age category may have an overly large representation of individuals of one nationality. These individuals could be genetically different from individuals in another age category composed largely of people with a different nationality and genetic makeup. As another example, some cross-sectional studies show that there is a decrease in intelligence with aging. This difference may be due not to aging but to less opportunity and encouragement for those in the old-age categories to have attended school in their youth. This last problem can be identified by performing a time-lag study. It carries out the same cross-sectional study procedure after many years and makes comparisons between two groups of the same age category. For example, measurements of people who are 65 years old in 1990 could be compared with measurements of people who are 65 years old in 2010. Differences between these groups would reveal effects from differences in historical conditions.

 

Another design flaw in these studies is called differential mortality. It means that because of inborn differences in susceptibility to certain causes of death (e.g., certain infectious diseases), specific groups of individuals who would have been included in certain age categories have been inadvertently selected out of their categories because they died before the study began. Thus, there is a built-in bias among the age categories that has nothing to do with aging.  Another problem with cross-sectional studies is that they measure only average changes. They cannot detect change in a single individual.

 

Overall, though cross-sectional studies sometimes detect true age changes, investigators using this technique may believe that they have found an age change where none exists. They also may conclude that an age change occurs faster or slower than it truly does.

 

Longitudinal Method

 

Another method for studying biological aging is the longitudinal study, in which a group of individuals of similar or identical chronological age is selected. Each individual is evaluated for the characteristics that are to be studied. Then, at specified intervals, the same individuals are evaluated in the same ways for the same characteristics. The intervals may be short, such as 1 year, or longer.

 

Longitudinal studies have several advantages over cross-sectional studies. First, they actually measure changes that occur as time passes; the relationship of the changes to aging is not simply inferred. Second, though they establish averages for a group as cross-sectional studies do, longitudinal studies can also detect age changes within the individual and can even establish the rate of change for each person. As a result, longitudinal studies reveal that different individuals age at different rates. As we will see later in this chapter, this is a very important finding.

 

By evaluating people periodically, longitudinal studies can also identify and measure the influence on aging of sudden events such as an accident or of long-term treatments or diseases. Alternatively, these studies can investigate the effects of aging on the course of a disease. Through careful analysis, longitudinal studies can establish the complicated interactive effects of several variables, such as the effects of changes in body weight on the way in which exercise affects the regulation of blood glucose. Finally, these studies can discover the predictive value of conditions present at one period of life on parameters such as future health and time of death.

 

Despite their many advantages, longitudinal studies on humans are not done as frequently as are cross-sectional studies because longitudinal studies have several negative characteristics. Of prime importance is the length of time needed to carry out such a study. It may be necessary to evaluate subjects over a period of many years. For example, if the study attempts to measure certain age changes from age 50 to age 80, the study must be conducted continuously for 30 years. During this period, many subjects may lose interest in the study, move away from the area where it is conducted, or die. The investigators themselves also face these problems. In addition, to achieve scientific reliability, the techniques for performing measurements of the characteristics of interest must remain basically the same despite technological advances. These factors cause a second drawback: Longitudinal studies usually cost a great deal more than do cross-sectional studies. Because of the expense, longitudinal studies usually include fewer subjects. Thus, after all the work, the results are not as statistically valid as those garnered from cross-sectional studies.

 

Longitudinal studies also contain certain design flaws. One is the period effect. For example, the results from a longitudinal study during a time of economic prosperity may be quite different from those obtained during a period of economic hardship. There is even a birth-cohort effect. This effect can be substantially reduced in longitudinal studies, but only by extending the studies over much longer periods.

 

Thus, while longitudinal studies can provide more and better information about biological aging than can cross-sectional studies, they do so only at great human and financial expense. Therefore, few long-term longitudinal studies have been conducted.

 

Baltimore Longitudinal Study of Aging   One of the largest and most successful continuing longitudinal studies is the Baltimore Longitudinal Study of Aging (BLSA). The BLSA is conducted by the National Institute on Aging, which is part of the National Institutes of Health, an agency of the federal government.

 

The BLSA started in 1958. At first it had only a few hundred male subjects, most of whom were at or beyond middle age. It now includes more than 700 volunteer subjects, both female and male, ranging in age from the twenties through age 90. Subjects receive a thorough evaluation, including numerous biological and psychological characteristics, every two to three years.

 

A third study method combines cross-sectional and longitudinal studies, forming a cross-sequential study. In this method, a cross-sectional study is performed and is then repeated after some years have passed. For example, people in five-year age categories extending from ages 40 to 70 could be evaluated in 1990, in 2000, and in 2010. Separate and combined comparisons could then be made among the groups at each time and among the three times. Using this complex method helps reduce problems from period effects, birth cohort effects, and differential mortality.

 

Nonhuman Studies

 

Besides being studied in humans, biological aging is studied in many animals, including mice, rats, flies, and worms. In addition, individual cells, both human and animal, are grown in nutrient materials to study biological aging. Though many of these studies have little or no immediate application to biological aging in humans, many others are used either as preliminary studies for future human studies or as experiments to support the results from human studies.

 

Animal and cell studies are very useful and important in the investigation of biological aging in humans since studying humans presents several problems. One is the genetic heterogeneity among people. This high degree of intrinsic variability results in considerable difficulty when one is interpreting data. Obviously, one cannot selectively breed people to achieve more genetic similarity among them, but selective breeding can be done with animals. Furthermore, environmental factors such as diet, temperature, and exercise can be controlled in animals to a degree that would be impossible in people. Even more control and freedom for study and experimentation are possible when one is dealing with individual cells.

 

Other factors make studying animals and cells desirable. Laboratory animals and cells take up less space, are less expensive to maintain, and have much shorter life spans than do humans. Unlike humans, certain lower animals (e.g., flies, worms) and cells apparently are not affected by psychological and emotional factors. Animals and cells can be humanely sacrificed for detailed anatomic and chemical analysis. Finally, unlike animals and cells, many elderly people have diseases and receive treatments that would affect the outcome of studies in which they might be subjects.

 

Still, humans must be studied directly if we are to increase our knowledge and understanding of the biology of human aging. It is known that aging in animals and individual cells differs from aging in humans in a variety of ways. For example, as some commonly used laboratory animals get older, they develop specific types of cancer and kidney disease that are not found in humans. Also, as some animals age, they have changes in hormone levels that are not seen in humans. The hormones involved may alter the aging processes in many parts of the body. Finally, certain chemicals and dietary substances are known to affect aging in animals differently from the way they affect aging in humans.

 

What We Know Thus Far

 

The study of biological aging became a topic of great interest only recently compared with areas of biology such as embryology, anatomy, and genetics. Although many fundamental questions about aging have not been addressed and others have been only partially answered, much has been learned in a short time. Research is continuing, expanding, and creating synergistic interdisciplinary bridges as the study of aging - gerontology - is undertaken by experts in more disciplines. Aging studies are also becoming more cross-cultural and international. These studies are revealing similarities and differences in aging among people of different cultures, races, regions, and national origins. Results from these comparisons are beyond the scope of this book. It deals with human aging in advanced Western civilizations, especially in the U.S.

 

What Happens during Biological Aging?

 

When Aging Begins   The ability of the body to maintain homeostasis seems to reach peak capacity peak during the third decade of life, after which age changes begin and bodily functioning starts to decline. (Fig. 1.12 (Fig. 1.12 HTML)). There seems to be no plateau period during which the body retains its maximum level of performance. The effects of aging are not immediately apparent, however.

 

Why Aging Appears Well after It Begins   One reason for delay in the appearance of age changes is the large reserve capacity present in many parts of the body. The heart, which can increase the amount of blood it normally pumps fivefold, and the respiratory system, which can move six times the amount of air normally breathed, provide two examples. Detrimental age changes draw first on such reserve capacities. The effects become apparent only when the body is called upon to function near peak capacity but much of the reserve is gone. Since biological aging occurs slowly and the body is rarely called upon to function at peak capacity, it takes many years for the reserves to become noticeably low. For example, some individuals reach age 40 or beyond before significant age changes are noticed. Additional normal aging must occur before body capacities become so low that a person seems impaired most of the time. As aging continues after that, impairments become so severe that they are classified as diseases. Eventually, body capacities are so low that homeostasis cannot be maintained even with medical assistance, and the person dies. Death is inevitable, but since the person has made the most of their biological life, they have aged normally.

 

The body behaves like a person who develops a large savings account when his or her income is high. That person can continue to live well by drawing on the savings when his or her income goes down. When savings become low, the person may not have enough funds to afford ordinary recreational activities, but essentials are still affordable. As funds dwindle, essentials become unaffordable, and the person may depend upon loans or other financial support. Eventually, funds become so low that the person is bankrupt.

 

Aging is like finances in two other ways (Fig. 1.12 (Fig. 1.12 HTML)). First, if a person does not develop to his or her peak potential during youth, they enter the declining years of aging with less reserve capacity. Malnutrition, poor health care, or other adverse circumstances during youth may produce this effect. With less reserve capacity when aging begins, less time is needed for the body to reach the impaired or diseased levels. Second, an adult with a high peak capacity may have their bodily reserves ravaged by aging plus by other adverse factors (i.e., misuse, disuse, disease). Again, impairment and disease develop more quickly. This latter scenario is common, so it has been called "usual" aging.

 

A second reason for the delay in the appearance of age changes in normal aging and in usual aging is the use of compensatory mechanisms. Some adjustments bolster diminishing functions. For example, greater amounts of chemicals (e.g., norepinephrine) that stimulate the heart are produced. This helps maintain pumping as the intrinsic strength of the heart declines. Some adjustments involve using more efficient ways to accomplish goals. People can learn how to pace themselves or use tools more effectively and thus continue to perform very difficult tasks. Finally, through changes in lifestyles and goals, many people tend to adjust their activities by participating in activities where they are comfortable and capable while shying away from activities that become too difficult and burdensome.

 

Variability in Aging There is considerable variability among people in both the age at which age changes are noticed and the rate at which these changes progress. This variability derives from several differences in aging (Fig. 1.13 (Fig. 1.13 HTML)). First, aging of a particular part of the body starts at different times for different people. Second, once a part has begun to age, it does so at different rates in different people. For example, bone strength declines faster in some individuals than in others. Third, the parts that age fastest in one person may not be the ones that age fastest in another person. Thus, one personís heart may have the most age changes, while in another person the lungs may be aging faster than the heart. Fourth, the rate of aging of most of one personís body parts is faster than the rate in another person. In other words, throughout the body, some people age faster than others. Because of all four differences, one person may begin aging or show signs of aging before a second person does. After some years, however, aging in the second person may surpass that in the first.

 

Two other types of variability in aging make this matter even more complicated. First, certain body parts usually seem to age faster than others do; for example, the lungs age faster than the blood. Second, though aging generally progresses steadily, the aging of some body parts in some individuals may speed up for a while, become quite slow for a while, and stop or show a reversal for a while.

 

Many factors combine in each person to affect the specific time of onset and rate of aging for each body part. Each individualís sex, genetically determined condition, and intrinsic compensatory powers when aging begins are unalterable factors. Occasional occurrences such as accidental injury and short-term diseases, along with long-term aspects of a personís life such as education, diet, exercise, occupation, air quality, and protracted diseases, also play a role both before and after aging begins. The rate and the degree of effects from the progressive changes caused by aging are altered as these factors change.

 

Therefore, though the rate of aging is determined in large part by conditions over which a person has no control, it is also heavily influenced by modifiable factors. As we identify and learn more about the factors that can be altered, we can gain more control over the progress of biological aging. We will also be better able to ward off the abnormal changes and diseases that become more likely as aging progresses.

 

Heterogeneity among the Elderly   Every individual is subjected to a unique combination of the factors that affect aging. Each factor acts at various ages to different degrees and for different lengths of time. The complex interactions among these factors add even more diversity. As a result, the older people get, the more different from one another they become. For many body parts, differences among those who have reached age 50 are already great. As more years pass, the heterogeneity among people expands more quickly. Some people become impaired or seriously ill at an early age, while other people remain hardy beyond age 100 (Fig. 1.12 (Fig. 1.12 HTML)). The elderly are the most diverse age group. Therefore, this book avoids using numerical values, which may be erroneously interpreted as ideals, norms, or goals. Some averages and ranges of values for the body are included, but only to provide approximations and trends within an expanding and increasingly diverse group.

 

An important consequence of heterogeneity among the elderly is the need to provide individualized treatment for them. As the age of a group of people increases, generalities apply less and less well to the individuals in that group. Any planning for elderly persons must consider this individuality. This would include, for example, evaluating eligibility for employment or educational opportunities, designing housing, developing nutritional programs, planning physical fitness programs, and providing health care. More attention to the increased differences among aging people would assure not only that more individuals will receive proper consideration but also that fewer will be subjected to detrimental care and therapy.

 

Another significant conclusion derived from increased heterogeneity with aging is that there is no set age at which a person becomes ďelderlyĒ. Although this book describes biological age changes observed frequently in people above age 50, that age was selected because most research on human aging has been done on people above age 50 and because many age changes do not become significant until after that age. Many individuals consider ďold ageĒ to begin at age 60, age 70, or even age 80 and beyond. Age 65, a figure commonly used to denote the onset of old age, was first used when the Social Security system was established. It was based on estimates of how long people should be fully employed so that there would be enough revenue to pay benefits to those who retired. Choosing age 65 really had nothing to do with aging. With changes in populations and government policies, the standard retirement age under Social Security has been changed to 67. This change occurred for demographic, economic and political reasons, not because it takes two additional years for people born after 1941 to become "old."

 

The Concept of Biological Age   Although there is no specific chronological age at which a person becomes biologically old, some researchers believe that determining it a personís biological age is possible. While there are several ways to do this, all of them start by attempting to determine average values for normal people at each chronological age. In one method, the levels of functioning of organs or systems are measured under resting conditions. In another technique, the levels of functioning are measured under stressful or maximum operating conditions such as during vigorous exercise. A third procedure measures the ability of the body to maintain normal conditions under adverse conditions, for example, the ability to maintain temperature while in a cold environment. Still another approach is to find the rate at which the body returns to resting conditions after being exposed to an adverse situation such as an excessive intake of salt.

 

Once the average normal values have been obtained, the measurements for the individual whose biological age is being determined are compared with those values. Scores for different functions may be considered individually, or a figure calculated from a combination of scores may be employed.

 

A simple procedure for carrying out the comparison would be to find the normal group whose average score equals that of the individual being considered. The individualís biological age could then be said to equal the chronological age of that group. Other types of comparisons of biological status among people of the same chronological age can establish the percentile rank of an individual within the group, as is done in comparisons of intelligence test scores.

 

The value of determining an individualís biological age can be greatly increased by repeating the procedure periodically, such as annually. This will provide information about the individualís rate of aging.

 

While any of these techniques can produce seemingly meaningful results, there is a lack of consensus about the validity of the procedures. Disagreements arise over which approach should be used. There is also the question of whether all the functions tested are equally important. If they are not, attempts to select the useful ones or to rank those that are used result in more discord. For example, should the ability to feel vibrations be included? What about clarity of eyesight? If these are included, is either of them more important than the resting heart rate? Or is maximum heart rate a better indicator of biological age? Then, too, are medically significant changes more important than those that affect a personís chosen lifestyle (e.g., physical pursuits, artistic pursuits, intellectual pursuits)? Perhaps an overall biological age but only separate biological ages for the various parts of the body.

 

Although this problem is far from resolved, attempts to find solutions are worthwhile for reasons similar to those that justify the study of biological aging. Once a biological age is determined for a person or a group of individuals, the factors that modify the aging processes can be discovered. This can lead to the formulation of improved care plans and can even lead to predictions of a personís life expectancy.

 

Life Expectancy

 

(These data are updated annually by the US Census Bureau and other agencies. Refer to the latest data and Updates for Chapter 1)

 

Maximum Longevity   How long can a person expect to live? The answer depends on many factors. The first factor to address is the one that establishes the longest life possible for humans. The longest life achieved by the members of a species is called the maximum longevity (XL) of that species. According to scientific records, the maximum longevity for humans is 122 years, the age attained by Jeanne Calment of France. In 1999, the oldest person was Sarah Knauss of Pennsylvania. Analysis of census and mortality data for the U.S. suggests that the human XL is probably 130 years. Human maximum longevity and the XL of other animals seem to be determined by genes. As described in Chap. 2, these genes may control activities such as the timing of life events, the time of death, the correcting of errors in other genes, and the repairing of molecules that carry out genetic instructions.

 

While the maximum longevity in some animal species can be changed by selective breeding and genetic manipulations, some scientists believe that maximum longevity for humans probably cannot be altered. This is due largely to several limitations to altering human genes. First, ethical considerations make selective breeding of humans impossible. Second, the genes that determine maximum longevity have not been identified. Even if they were identified, the ways by which they control life span are not known and therefore are not subject to manipulation. Third, if the information and techniques needed to perform the required genetic engineering are discovered, the question of whether such interference should be carried out remains. Ethical, social, political, and economic problems will need to be addressed.

 

Another reason militating against extending human XL derives from the techniques that might be required. The major discomfort or alteration in lifestyle caused by some procedures, such as the severe diet restrictions that lengthen the life span of some animals, might not be worth the possible gain in human life span. Some scientists believe that if these problems were solved, others, such as late life diseases not yet recognized, would become limiting factors. Finally, one would have to consider if having a longer life, with its many inevitable and unwanted age changes and increased likelihood of disease, is desirable.

 

Mean Longevity   Though humans can live to an age of 122 years, this rarely happens. Even reaching the age of 100 is considered remarkable. One reason people live to different ages is the variation in genes controlling life span. Additionally, people are subjected to many other causes of death, such as accidents and disease. These other causes act before the genes determining life span have an opportunity to do so. Therefore, a statistic that is more useful for most people than maximum longevity is mean longevity (ML), the average age at which death occurs for the members of a population; this is also called the life expectancy of the population. The conditions that determine mean longevity provide the second part of the answer to the question of how long a person can expect to live. These conditions reduce life expectancy to a value less than maximum longevity.

 

Statistically speaking, all people in a population have the same mean longevity at the time of birth. However, different populations have different MLs. One reason for this is the historical period in which birth occurred. For example, the mean longevity in America in 1776 was 35 years. By 1900 it had increased to about 47 years. It reached slightly over 68 by 1950 and climbed to almost 74 years of age by 1980.

 

Between 1900 and 1970 the increase in mean longevity was due mostly to a decrease in the death rates of infants and children. Early in this period, poor provisions for public health (e.g., sanitation) and weak control of infectious diseases (e.g., vaccinations, antibiotics) were the main causes of high infant and child mortality (Fig. 1.5 (Fig. 1.5 HTML)). Harsh working conditions and limited education further shortened the lives not only of children but also of adults. The result was that few people lived long lives. As environmental and other external conditions improved, many more people survived the first few decades of life, and this led to a dramatic increase in mean longevity (Fig. 1.6 (Fig. 1.6 HTML)).

 

Mean longevity in the United States has continued to rise since 1980. It reached 74.0 years for men and 79.4 years for women by 2000 and is expected to reach 76.5 for men and 80.8 for women by 2020. It will probably rise slowly but steadily well beyond the year 2030, reaching as high as 80.1 for men and 83.9 for women by the year 2060. Most of this increase is due more to decreased death rates for those above age 35 than to changes in death rates among younger people. The reason is that so much progress has been made in improving the extrinsic conditions that affect younger people that few advances in this area can be expected. Intrinsic factors and chronic diseases, which come into play in the later years of life, now have a more predominant influence on ML because they have become the main causes of death. This situation is expected to continue as long as human activity does not cause additional deterioration of the environment or become more self-destructive.

 

Reasons other than historical periods cause differences among populations in mean longevity at birth. For example, gender affects mean longevity (ML). The population consisting of all women has a higher ML than does the population of all men. One factor contributing to this higher mean longevity seems to be that higher levels of certain hormones (estrogen and progesterone) help protect women from specific serious diseases (e.g., heart attacks). Another possible factor among women may be that female cells can use more of the genetic material (i.e., sex chromosomes) they contain. A third possible factor is that women have less iron before menopause due to periodic menstruation. With lower iron, women may sustain less damage to their molecules from free radicals (see Chapter 2). A fourth factor may be that over the past decades, lifestyles and careers traditionally involving primarily women provided less danger and stress than did those involving primarily men. Finally, men may be more willing to take serious physical risks.

 

Another important factor affecting mean longevity is race. The white population has a higher mean longevity at birth than does the black population. Like the differences in mean longevity between women and men, these differences are probably due to differences in both genetics and lifestyle factors (e.g., nutrition, education, employment).

 

The differences in mean longevities between sexes and among races and cultures have always existed in the United States, but the degrees of difference have not always been the same. Most recently the differences have been decreasing. It is uncertain whether these differences are more likely to decrease or increase in the next several decades.

 

While all members of a population have the same mean longevity at birth, the mean longevities of individuals of different ages in that population are different (Fig. 1.6 (Fig. 1.6 HTML)). This is the case because as time passes, the death of some members of each birth cohort selects out those who do not survive well. This selection process spares those in the population who have better intrinsic characteristics for survival, better living conditions, or better mechanisms to adapt to life-shortening situations. These survivors thus have higher life expectancies. Thus, the life expectancy of those who were born in 2010 is age 76.2 years for men and 81.0 years for women, while the life expectancy of those who were 65 years of age is 82.7 years for men and 85.3 years for women. For those who were 75 years old in 2010, the corresponding figures are 86.0 and 87.9 respectively. (Table 15. Life expectancy at birth, at age 65, and at age 75, by sex, race, and Hispanic origin: United States, selected years 1900Ė2016 [https://www.cdc.gov/nchs/data/hus/2017/015.pdf]).

 

 

Thus far we have looked at life expectancy in broad terms. We will now point out a few examples of additional factors that help determine how long a person can expect to live.

 

Some factors that influence life expectancy are fixed at birth. Here we must again mention genes. People who have parents who lived long lives tend also to live long lives. In fact, the more blood relatives with long lives a person has, the greater the chances that person has of living a long life. This is due only in part to the genes passed from one generation to the next, however. It is also due to the nurturing and culture that members of a family share.

 

Two other influential characteristics that are not easily changed are intelligence and personality. Overall, people with higher intelligence and people with personalities that result in lower stress levels tend to live longer. By contrast, those whose personalities provide more stress, especially highly competitive perfectionists with a persistent sense of lacking sufficient time to accomplish their goals, tend to have lower life expectancies.

 

While intelligence and personality are partly established by the time of birth, they can be modified by the environment to which an individual is exposed. Good education and positive social relationships can significantly shape and strengthen intelligence and personality, resulting in an increase in life expectancy.

 

Though we have virtually no control over which genes people inherit, we can exert much influence over the environment in which people develop and live by providing conditions and opportunities known to increase life expectancy. People tend to live longer if they have proper nutrition, housing, and health care. Being employed, being married, having an adequate income, and receiving more education also increase life expectancy. Avoiding or reducing exposure to environmental insults (e.g., air pollution, smoking, excessive alcohol, toxic chemicals, radiation) are also positive influences. Living in areas where accidents are minimized also improves the chances for a longer life. Of course, preventing diseases makes a substantial contribution in this regard. Note that disease prevention is only one of many factors that increase life expectancy. It has been estimated that even if the diseases that are the top 10 causes of death were eliminated, mean longevity would increase only 11 years.

 

There are, then, many conditions affecting life expectancy over which we have considerable control. Interestingly, these factors not only increase life expectancy, they also greatly affect the quality of life, including life in the later years. Modifying conditions to improve the quality of life is perhaps an even more important goal than modifying them simply to extend the length of life. Furthermore, just as with planning for our financial future and retirement, the sooner we get started and the more regular our contributions, the greater the chances for happy and successful aging.

 

Status of an Individual   Thus far, we have dealt with mean longevity, the average life expectancy for a group of people. Attempting to estimate the life expectancy of one individual would require considering all factors affecting the group. However, more information about the current biological status of the individual would also be very helpful. This is where a medical checkup or a determination of the personís biological age becomes quite useful. An even better estimate of life expectancy can be formed if the individual is evaluated regularly to detect changes in the ability to maintain homeostasis. This can identify problems early in their development. Then steps can be taken to ward off or to compensate for the oncoming difficulty. An increase in life expectancy and in the quality of life in the years remaining could result.

 

Just how long can a person expect to live? There are certain limits within which the answer lies. Although rough estimates can be made, finding the answer with accuracy is difficult. The answer depends on the unique combination of several factors that are present in a personís life. Also, as the types and intensities of these factors change, the answer also changes. Perhaps we should be satisfied with the rough estimates and devote more time and energy to improving the quality of life we have left as we age.

 

Quality of life

 

Quality of life can be evaluated in several ways. When determining the quality of life of others, evaluators usually use quantitative observable parameters and use tests and interviews. A person's status in several areas may be evaluated including physical health, ability to perform activities of daily living (e.g., dressing, bathing, eating, mobility), psychological status, emotional status, economic status, social functioning, and involvement with life activities. When determining one's own quality of life, many elders use parameters different from those used by others who evaluate them. Elders often consider factors related to self-identity, sense of independence, sense of self-efficacy, sense of control of one's environment and life, and life satisfaction.

 

Evaluating quality of life and determining how to evaluate it for individuals is important in developing public policies (e.g., health care, retirement plans) and individual courses of action (e.g., purchases, finances, health care, family matters). Also, determining quality of life is needed when assessing outcomes. Through the interactions between the biology of the body and perceptions, quality of life affects health status, mean longevity, and how much contribution elders can make to society.

 

Chapter 1 beginning

 

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© Copyright 2020 - Augustine G. DiGiovanna, Ph.D., Salisbury University - All rights reserved. Except as permitted under the United States Copyright Act of 1976, no part of this page or accompanying pages may be reproduced or distributed in any form or by any means, or stored in a data base or retrieval system, without the prior written permission from Augustine G. DiGiovanna, Ph.D., Salisbury University .