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8 Conclusions The elderly constitute the fastest-growing segment of the pop- ulation in many industrial countries. This unprecedented demo- graphic phenomenon is occurring at a time of increasing complex- ity of environmental factors, including pollutants, pharmaceutical use, nutrition, and life-style. The impact of these environmental phenomena on aging processes and the aged is not well under- stood, but there are sound biologic reasons to assume that the effect of the environment on people changes with age, as does the ability to respond to environmental exposures. In addressing the issues related to aging in today's environ- ment, one must recognize at least three important questions: What is the nature of aging? What is the nature of the environmental exposure? What is the physiologic or medical condition of the aging or ages] subject or population? The nature of the aging processes has been a question since humans have been aware enough of themselves to ask it. Not much progress has been made toward answering it. Environmental exposures vary greatly among individuals. Such exposures might well be more problematic for the aged, especially those with existing chronic diseases. Over 70~o of the aged take one pharmaceutical regularly; and heart disease occurs in over 25~o. These changes in physiologic and medical conditions 162
CONCLUSIONS 163 of aging reflect the effects of the environment on intrinsic aging processes integrated over a person's lifetime. In addition, it should be understood that the term aged means different things to different people. More important, aged simply refers to a portion of the normal distribution of ages In any pop- ulation defined by any number of objective, functional, or other · criteria. After extensive review of the current state of the science and after deliberation of the above questions, the committee drew the following conclusions. Evidence supports the concept of intrinsic aging, and many theories have provided insight into its basic mechanisms. Numer- ous components of the environment have been shown to cause changes that simulate and are often confused with features of in- trinsic aging. For example, habitual sun exposure and cigarette smoking accelerate aging of the skin, exposure to ultraviolet ra- diation promotes cataract formation, and exposure to naturally occurring or industrial or other toxicants can contribute to age- related neurologic disease. However, no single agent has ever been shown to cause the earlier appearance of at! aging processes. Humans exhibit varied responses to the environment and var- ied patterns of aging. The variation can be attributed to many factors, which include the following: . Differences in individual environment, including nutrition, pharmaceuticals, lifestyle, and occupation. . Inborn genetic differences, such as variations in genes that influence susceptibility to graying of the hair, cataract formation, diabetes, aging of sun-exposed skin, and metabolism of drugs. . Interactions between individual genetic constitutions and the environment. Information on the specific impact of environmental factors on aging processes remains scant. However, experimental animal studies of dietary restriction and genetic manipulations (e.g., set lective breeding) that extend the life spans of some laboratory animals are promising tools for the study of aging processes and the impact of the environment on them. With regard to the human aged, not enough is known about the specific effects of environmental exposures, but there is much evidence of their importance. Consider the following, for example:
164 AGING IN TOD~Y'S ENVIRONMENT ~ Extremes of air pollution or environmental temperature that are tolerated by young adults can be injurious, even fatal, to the elderly. . Although the judicious use of medications undoubtedly contributes to the overall well-being of older persons, they suffer adverse reactions to drugs more frequently than the young. The extent to which that is due to dmease severity, use of multiple drugs, drug misuse, or age itself is unknown. Older persons are often more susceptible than young adults to the effects of environmental toxicants. ~ A decrease in smoking, an increase In exercise, control of hypertension, and dietary modification appear to decrease or delay the occurrence of heart disease, stroke, and some types of malignancy. Interpersonal relationships can have substantial positive effects on various physical health indexes, and sense of purpose is closely tied to the health and well-being of the elderly. There is evidence of greater survivorship among people who have goals than people who do not, en c} among those who have organize tion in their daily lives and behavior than those who do not. Health-care providers, in nursing homes in particular, should be educated about the benefits to the elderly of increased autonomy and friendships. Although the increased incidence of chronic dmeases is often associated with aging, such diseases need not be characteristic of the aging processes. The wide variation in the incidences of chronic diseases in the aged in different countries strongly indicates that much of the prevalence of these diseases might be preventable. One appealing and testable hypothesis is that reduction of dmease in old age is an attainable objective that can be approached, in part, through modification of the environment. Research in this field will likely lead to an improved understanding of the interplay between aging processes, the environment, and disease and help to provide the key to preventing environmentally induced age- associated diseases.
