As we age, our bodies change in many ways that affect the function of both individual
cells and organ systems. These changes occur little by little and progress inevitably
over time. However, the rate of this progression can be very different from person
to person. Research in aging is beginning to find out the reasons for these changes
and the genetic and environmental factors that control them.
- Genetic and Environmental Factors
- Healthy Lifestyle Behaviors
- Cellular Changes Associated with Aging
- Bodily Changes Associated with Aging
- Changes in Height
- Changes in Weight
- Changes in Body Composition
- Other Changes with Aging
- Normal Aging and Disease
- Changes in the Regulation of Body Systems
Genetic and Environmental Factors
The aging process depends on a combination of both genetic and environmental factors.
Recognizing that every individual has his or her own unique genetic makeup and environment,
which interact with each other, helps us understand why the aging process can occur
at such different rates in different people. Overall, genetic factors seem to be
more powerful than environmental factors in determining the large differences among
people in aging and lifespan. There are even some specific genetic disorders that
speed up the aging process, such as Hutchinson-Gilford, Werner’s, and Down syndromes.
However, many environmental conditions, such as the quality of health care that
you receive, have a substantial effect on aging. A healthy lifestyle is an especially
important factor in healthy aging and longevity (see Prevention). These environmental
factors can significantly extend lifespan.
Behaviors of a Healthy Lifestyle
- Not smoking
- Drinking alcohol in moderation
- Getting adequate rest
- Eating a diet high in fruits and vegetables
- Coping with stress
- Having a positive outlook
Cellular Changes Associated with Aging
Aging causes functional changes in cells. For example, the rate at which cells multiply
tends to slow down as we age. Certain cells that are important for our immune system
to work properly (called T-cell lymphocytes) also decrease with age. In addition,
age causes changes in our responses to environmental stresses or exposures, such
as ultraviolet light, heat, not enough oxygen, poor nutrition, and toxins (poisons)
Age also interferes with an important process called apoptosis, which programs cells
to self-destruct or die at appropriate times. This process is necessary for tissues
to remain healthy, and it is especially important in slowing down immune responses
once an infection has been cleared from the body.
Different diseases that are common in elderly people can affect this process in
different ways. For example, cancer results in a loss of apoptosis. The cancer cells
continue to multiply and invade or take over surrounding tissue, instead of dying
as originally programmed. Other diseases may cause cells to die too early. In Alzheimer’s
disease, a substance called amyloid builds up and causes the early death of brain
cells, which results in a progressive loss of memory and other brain functions.
Toxins produced as byproducts of nerve-cell transmissions are also thought to be
involved in the death of nerve cells in Parkinson’s disease.
Bodily Changes Associated with Aging
Our bodies normally change in appearance as we age.
Changes in Height
We all lose height as we age, although when the height loss begins and how quickly
it progresses vary quite a bit among different people. Generally, our height increases
until our late forties and then decreases about two inches by age 80. The reasons
for height loss include the following:
- changes in posture
- changes in the growth of vertebrae (the bones that make up the spine)
- a forward bending of the spine
- compression of the discs between the vertebrae
- increased curvature of the hips and knees
- decreased joint space in the trunk and extremities
- joint changes in the feet
- flattening of the arches
The length of the bones in our legs does not change much.
Changes in Weight
In men, body weight generally increases until their mid-fifties; then it decreases,
with weight being lost faster in their late sixties and seventies. In women, body
weight increases until the late sixties and then decreases at a rate slower than
that of men.
People that live in less technologically developed societies do not show this pattern
of weight change. This suggests that reduced physical activity and changes in eating
habits may be causes of the change in body weight rather than the aging process.
Changes in Body Composition
The proportion of the body that is made up of fat doubles between age 25 and age
75. Exercise programs may prevent or reverse much of the proportional decrease in
muscle mass and increase in total body fat. This change in body composition is important
to consider in nutritional planning and level of activity. The change in body composition
also has an important effect on how the body handles various drugs. For example,
when our body fat increases, drugs that are dissolved in fatty tissues remain in
the body much longer than when our body was younger and more muscular.
Other Changes with Aging
Normal aging in the absence of disease is a remarkably benign process. In other
words, our body can remain healthy as we age. Although our organs may gradually
lose some function, we may not even notice these changes except during periods of
great exertion or stress. We may also experience slower reaction times.
Normal Aging and Disease
Aging and disease are related in subtle and complex ways. Several conditions that
were once thought to be part of normal aging have now been shown to be due to disease
processes that can be influenced by lifestyle. For example, heart and blood vessel
diseases are more common in people who eat a lot of meat and fat. Similarly, cataract
formation in the eye largely depends on the amount of exposure to direct sunlight.
We should remember that there is a range of individual response to aging. Biologic
and chronologic ages are not the same. In addition, body systems do not age at the
same rate within any individual. For example, you might have severe arthritis or
loss of vision while the function of your heart or kidneys is excellent. Even those
aging changes that are considered "usual" or "normal" are not inevitable consequences
Changes in the Regulation of Body Systems
The way our body regulates certain systems changes with age. Some examples are listed
- Progressive changes in the heart and blood vessels interfere with your body’s ability
to control blood pressure.
- Your body cannot regulate its temperature as it could when you were younger. This
can result in dangerously low body temperature from prolonged exposure to the cold
or in heat stroke if the outside temperature is too high.
- There may be aging-related changes in your body’s ability to develop a fever in
response to an infection.
- The regulation of the amount and makeup of body fluids is slowed down in healthy
older persons. Usual (resting) levels of the hormones that control the amount of
body fluids are unchanged, but problems in fluid regulation commonly develop during
illness or other stress. Also, elderly people don’t feel as thirsty after water
deprivation as they did when younger.
What do these age-related changes in our body systems mean?
- First, with advancing age, we become less like each other biologically, so our health
care needs to be more individualized.
- Body systems that can be minimally affected by age are often profoundly influenced
by lifestyle behaviors such as cigarette smoking, physical activity, and nutritional
intake, and by circumstances such as financial means.
- Finally, it’s helpful to consider ahead of time our possible choices in case certain
situations arise. For example, if you become less physically able to take part in
an athletic activity you did before, is there a different activity you might enjoy?
Are there things you might like to do to keep your mind active? More serious situations
to consider might include death of a spouse, or if you find your abilities becoming
more and more limited. Have you discussed how you would like to handle such situations
and your wishes with your family?
It is important to remember that the ability to learn and adjust continues throughout
life and is strongly influenced by interests, activities, and motivation. With years
of rich experience and reflection, we can rise above our own circumstances. Old
age, despite the physical limitations, can be a time of variety, creativity, and
Source: AMERICAN GERIATRICS SOCIETY: