health care opportunities created by work, with their effect on overall socioeconomic status, which is an extremely powerful determinant of the future occurrence of diseases, illnesses or disorders, disability, and death (Adler and Newman, 2002). The intimate association between types of work and the socioeconomic context in which that work takes place makes understanding the health impact of various workplace exposures extremely complex. In addition to prior and current workplace exposures, the trajectory of health and aging will be substantially affected by nonwork-related environmental, physiochemical, and social exposures, such as recreational and other avocational activities, intentional and unintentional injuries, communicable diseases, and unhealthy hygienic behaviors such as tobacco, alcohol, and other substance abuse, careless automobile driving habits, inadequate exercise, unhealthy diets, and many other risk-taking behaviors.

The nature and causes of age-related changes in individuals and populations are complex and in general beyond the scope of this volume. While theories abound, no one has identified a unique cause or biological process that is pure aging. Rather, there are a very large number of age-related changes that involve every bodily system and function to a greater or lesser extent. To the extent that these individual changes have been investigated, age-related change rates in individual bodily organ and system functions do not necessarily track at the same pace. The difference between the mechanisms of aging and disease pathogenesis may also be more apparent than real, with many common causes and opportunities for interdiction. For example, cigarette smoking accelerates the age-related decline in lower extremity function (Bryant and Zarb, 2002) as well as causing lung cancer and coronary heart disease.

Thus, removing or limiting many toxic environmental exposures, particularly the intensive ones that can occur in the workplace, may lead to lower disease rates and improved maintenance of general human function, irrespective of whether the intervention affects aging or disease pathogenesis. Disease phenomena, particularly the large number of chronic conditions that increase in frequency with age, have very important implications for health status and outcomes, including among older workers, but distinguishing a disease from other aging manifestations is often arbitrary or one of degree. Thus, it may be useful to consider aging as age-related change, in reality a large set of important but at least partly malleable processes and functions that are not necessarily biologically obligate or fully predetermined (Arking, 1998).

Observations from the gerontological and geriatric literature enhance the understanding of age-related change. Importantly, this approach avoids attributing older worker performance or function to aging, which may convey an erroneous prospect of immutability or nonpreventability. An example may be lower extremity pain or dysfunction, often related to



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