Introduction
The human life span (the length of time people may live under optimal conditions) is about 120 years. Although this figure has not changed over the last century, life expectancy has. The amount of time an American baby can be expected to live has increased from under sixty years if born in 1900 to nearly seventy-nine years if born in 2010, according to a 2013 report by the Centers for Disease Control and Prevention. As people have begun to live longer, they have become aware of many changes that occur as they age. The scientists who study aging are called gerontologists. It is known that predictable changes occur in the body as it gets older. Some are easily noticed, such as graying or thinning hair and wrinkles. Other changes, such as a tendency toward rising blood pressure, are not visible.
In general, research on aging has emphasized losses. More recently, increased interest in the aging process has stimulated physiological, sociological, and psychological research on aging. Although many physiological variables show major losses with advancing age, it is important, when looking at the average, to note that there is substantial variability at all ages throughout life. Scientists have found that some changes in blood pressure and cholesterol levels that had originally been interpreted as age specific are common in industrial societies but not in agricultural ones.
Changes in Body Systems with Age
One of the major physical changes that occurs with age is an increase in reaction time. As one gets older, it takes longer to respond to a stimulus. This increased reaction time is due to a number of factors, including changes in sensory function, an increased concern for accuracy, a slower response (often due to arthritis), and a slowing of transmission of neural impulses. This slowdown in the transmission of impulses through the nervous system is due in large part to demyelinization. As the axons lose their fatty covering (myelin sheath), saltatory conduction is impaired, and slowing of the neural impulse occurs.
Advancing age is associated with progressive impairments in the capacity to metabolize glucose. Again, there is substantial variability in the results for successive age groups, with many older individuals metabolizing glucose as well as their younger counterparts. The carbohydrate intolerance of aging may carry substantial risk, even in the absence of disease. Attempts have been made to determine which components of the age-associated alterations in carbohydrate intolerance are related to aging itself and which components might be related to diet, exercise, or medications. It is thought that factors such as physical fitness may decrease the likelihood of carbohydrate intolerance with advancing age. Metabolism
also begins to slow at around age twenty-five. For each decade thereafter, the number of calories required to maintain one’s weight drops by at least 2 percent. Muscle mass gradually shrinks, so older people tend to have more body fat than they did when they were younger.
Aging is also associated with a decline in bone density in both men and women, but primarily women. Osteoporosis, a condition in which the bones become dangerously thin and fragile, is a major problem for the elderly. Bone mass reaches its peak in the thirties for both men and women and then begins to drop by about 1 percent per year. Brittle bones are the major cause of the fractures, particularly in the vertebrae and hips, that cripple many of the elderly. A number of studies suggest that bone loss can be reduced in advanced age by adherence to moderate exercise programs, in addition to adequate calcium intake throughout life. Drugs such as calcitonin-salmon (Miacalcin) and alendronate sodium (Fosamax) have been developed to treat osteoporosis.
Arthritis (inflammation of the joints) is one of the common complaints of middle-aged and elderly adults. Osteoarthritis is the type that most commonly develops with age. It leads to stiffening of the joints, along with pain. As a result, people may tend to exhibit decreased mobility and slowing of their responses. Arthritis has long been treated with corticosteroids. Pain is often treated using nonsteroidal anti-inflammatory drugs (NSAIDs). Recent research has focused on the use of glucosamine and chondroitin to treat arthritis. Joint replacement is available as an option to treat advanced arthritis.
The senses
of the elderly and the associated organs also go through changes. Taste diminishes as the nose loses its sense of smell. Odors account for most of the overall sensation of flavors, so taste is lost as a function of loss of smell. Loss of taste can lead to lack of appetite and to serious nutritional deficiencies.
Hearing also fades, particularly in the high-frequency range, resulting in presbycusis. This high-frequency hearing loss with age begins at age twelve, and involves a loss of fifty cycles per second per year (beginning with a maximum frequency of twenty thousand cycles per second). Pathological hearing loss also is found as people age and often seems to relate to exposure to noise pollution. As a result, it has been seen more commonly in men (as a result of participation in wars and noisy work environments) and is expected to increase in frequency in the future as a result of the use of loud electronic equipment and headphones. Pathological hearing loss is of great concern to gerontologists and geriatricians because it is often denied by the elderly, who then do not seek treatment and often develop interpersonal isolation and paranoid behavior as a result.
Vision changes also commonly occur with age. Beginning at about age forty, people become aware that they have difficulty reading and seeing close up. By the age of forty-five, a majority of adults wear glasses or contact lenses to correct for presbyopia (farsightedness that develops with age). Other visual disturbances that may occur with advancing age include cataracts (opacity of the lens of the eye) and glaucoma (increasing intraocular pressure). Additionally, the elderly lose the ability to see color at the shorter wavelengths, so that violet and navy come to be seen as black.
As adults get older, they also become less sensitive to pressure and therefore more likely to develop bedsores or skin ulcerations. Temperature regulation also becomes impaired, so that the elderly are often too hot or too cold. Sense of balance is also less precise, so presbystasis (lack of sense of balance with age) occurs, making falls more likely. Changes occur in the skin: The topmost layer, or epidermis, becomes dry, whereas the middle layer, or dermis, becomes thin and less elastic. Along with loss of fat from the underlying subcutaneous layer, these changes cause the skin to sag and become wrinkled.
There are other physiological changes that accompany aging. For example, the immune system starts to decline in young adulthood. The white blood cells that fight off invaders such as viruses and bacteria lose some of their effectiveness as a person gets older. Antibody production in people over the age of sixty-five is less than 10 percent of what it was in adolescence. As a result, the older adult is much more susceptible to illness than the adolescent or young adult. Thus, the elderly are advised to get flu and pneumonia shots to help keep themselves healthy.
The respiratory system undergoes many changes with age. There is a reduction in breathing efficiency because the lungs no longer expand to take in as much air. In fact, lungs lose, on the average, 30 to 50 percent of their maximum breathing capacity between ages thirty and eighty. The uptake of oxygen in the lungs is diminished, so less oxygen is carried by the blood, which has health ramifications since oxygen is necessary for the synthesis of amino acids and fatty acids and for the production of energy.
Theories of Aging
Virtually all systems of the body, including the cardiovascular, circulatory, endocrine, excretory, and gastrointestinal systems, show changes with age. Several theories on aging attempt to explain the aging process. The aging of cells is a complex process that scientists still do not completely understand. There are genetic theories, as well as nongenetic and physiological ones. Genetic and nongenetic theories of aging both explain aging at the cellular or molecular level.
Genetic theories assume that a problem occurs in cell formation with age. This problem occurs at the level of the ribonucleic acid (RNA) or deoxyribonucleic acid (DNA). Error theory is the genetic theory best supported by evidence, and it assumes that aging is most likely to occur as a result of a change in RNA.
Nongenetic theories assume that cell formation occurs normally with age but that something interferes with cell functioning as one ages. Wear-and-tear theory and accumulation theory are two of the best-supported nongenetic theories. The buildup of free radicals in the cell (which fits accumulation theory) has led to the popular use of antioxidants (nutritional supplements) to try to slow the aging process.
Physiological theories assume that aging occurs at the molar level—the level of tissues, organs, or systems. These theories attribute aging to a breakdown in the integration and function of systems. Evidence indicates support for some genetic, nongenetic, and physiological theories, indicating that each may play a role in bringing about the physical changes of aging.
Trends in Aging
The number of elderly people in the United States increased rapidly in the second half of the twentieth century and the first decade of the twenty-first. Americans are living longer than ever before. According to a 2011 report by the Administration on Aging, a division of the US Department of Health and Human Services, by 2030 there will be as many as 72 million Americans age sixty-five or older. This demographic is projected to make up 19.3 percent of the population, up from about 13 percent in 2010.
One popular misconception disputed by recent research is the idea that aging means inevitable physical and sexual failure. Although some changes necessarily occur, many of the problems associated with old age fall into the category of secondary aging. Such problems are not the result of age but of abuse and disuse, which often can be controlled by the individual. Researchers have found that people wear out faster from disuse than they wear out from overuse. This also applies to sexuality. Studies from the time of Alfred Kinsey’s work in the 1940s and 1950s to the early twenty-first century show that sexual interest and activity decrease with age, but the drop varies greatly among individuals. Psychologist Marion Perlmutter reported that one of the best predictors of continued sexual intercourse is past sexual enjoyment and frequency. People who have never enjoyed sexuality much may consider age a good reason to give up sex.
Psychosocial factors have been studied, and they sometimes reveal how older men and women feel about the physical changes happening to their bodies. It is important that family members and members of the helping professions, along with the elderly themselves, come to understand that the physical changes that occur with passing time produce needs that are real and that elderly people are not simply trying to make demands for attention. Elderly people must be allowed to retain their dignity and to remain as active and independent as possible. No one, at whatever age, likes to be helpless or to be perceived as helpless. As a result of helplessness, researchers find lowered self-esteem, health problems, depression, and sometimes death.
Several lines of research on psychosocial factors and health focus on the idea of social support. Empirical research has found consistent relationships between social support and various indicators of health and well-being. Social networks and support are persistent conditions that affect the mortality of older people. Support-disrupting life events have specific negative effects on both mortality and morbidity. The positive effects of social support have been demonstrated by means of intervention studies. Most of the intervention has involved supportive behaviors by health care professionals. Positive effects include increased rate and completeness of recovery from injuries, a smaller number of heart attacks, decreased incidence of cancer, and fewer physical illnesses.
Studies on Aging
Important early studies of aging were performed in the 1950s, including the Human Aging Study, conducted by the National Institute of Mental Health; the Duke Longitudinal Studies, done by the Center for the Study of Aging and Human Development at Duke University; and the Baltimore Longitudinal Study of Aging. These pioneering studies and hundreds of others have benefited from growing federal support.
The Human Genome Project (especially Project Chronos) is among studies important in the field of aging. These studies continue to investigate the changes that take place in aging, as well as attempting to find ways to stop or delay these changes. In contemporary society, many people reaching one hundred years of age (centenarians) continue to function very well, showing minimal physical change with age. As these people are studied in projects such as Chronos, perhaps humankind will find an answer to the biological changes in aging, as well as finding ways to delay such changes.
Bibliography
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Centers for Disease Control and Prevention. "Life Expectancy." CDC. Centers for Disease Control and Prevention, 21 Nov. 2013. Web. 21 Feb. 2014.
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