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Chapter 1 - Introduction -
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 one’s 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.
(Suggestion
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). 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). These data and projections for 2021 and thereafter will change due to
substantial changes in immigration since 2010 and effects from the Coronavirus
COVID-19 pandemic that began in early 2020.
There will also be an increase in both the number and
proportion of people of higher ages (Fig.
1.1, Fig.
1.2 Graph) and Fig.
1.2 Web Sites). 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). A second is the high number of births between 1946 and 1964 (Fig.
1.4 ). A third factor is the decline in childhood death rates, especially
during the first year of life (Fig.
1.5). 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). 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). 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 effects from the Coronavirus COVID-19 pandemic that began in
early 2020 are ongoing. 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.
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 “artificial” 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 person’s
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.
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 person’s ability to survive or a person’s 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). By contrast, bones contain some bone cells but consist mostly
of materials that those cells secrete (Fig.
1.8b).
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 (i.e., continuing good health). 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). 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). 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 (i.e., from continuing good health). 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). 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 (i.e., from continuing good health).
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 (i.e., continuing good health) 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 (i.e., continuing good health) 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 person’s 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 person’s
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 person’s chronological age. However, it is an inaccurate
indicator for either purpose because of variation among individuals and because
a person’s 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 person’s 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 person’s 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 person’s 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 person’s 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 one’s soul (Soul), its importance, and its
status
· a sense of well-being
· death, including one’s own and that of others
· essential motivations
· fundamental values and what are of essential importance
· hardship and suffering
· one’s interior mental thoughtful life
· one’s true essential nature – what constitutes one’s
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 one’s self
· one’s 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 one’s conduct
· relationships with a Creator, God (by any name), gods, and
supernatural beings
· overall success and accomplishment in life
· purpose for existing and one’s 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).
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 “usual” age changes by
some authors. People who avoid these abnormal changes while undergoing normal
age changes are said to have achieved “successful” 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 person’s
body has any one of three characteristics; (1) it has homeostasis (i.e., continuing good health) 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 Alzheimer’s 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 person’s lifestyle. Early detection is
important because it greatly increases the success achieved by treatment.
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 be 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 person’s 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.
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.
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.
(Suggestions 13-02-04)
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.
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.
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 (i.e., continuing good health) 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). 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). 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). 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
person’s 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
person’s 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. (Suggestion:
Chap 01 - 16-2-1)
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 individual’s 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 person’s 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). 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
“elderly”. 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 “old age” 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 person’s 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 individual’s 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 individual’s biological age can
be greatly increased by repeating the procedure periodically, such as annually.
This will provide information about the individual’s 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 person’s 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 person’s 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. (Suggestion 19.01.04) (Suggestion 19.01.05)
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. (Suggestion 18.02.03)
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). 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).
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). 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 1900–2016
[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
person’s 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 (i.e., continuing good health). 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 person’s 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 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. (Suggestion 21.02.02)
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. (Suggestion 21.02.01)
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