degenerative arthritis, an entity that is at least partly preventable and susceptible to treatment and rehabilitation. Many important age-related changes may begin in youth or midlife, which can allow early detection with physiological or other performance testing. Regardless of the causes of these early changes, early physiological abnormalities or behavioral changes can predict later overt dysfunction and disease (Whetstone et al., 2001), allowing the observational and experimental studies of possible interventions. However, not all age-related changes occur in slow, continuous decrements. Not only do acute changes in health and function occur with certain diseases and conditions, such as with injury and acute infectious diseases, but also with the rapid emergence of chronic diseases such as cancer, heart disease, and stroke (Ferrucci et al., 1996). This highlights the role of clinical disease prevention in deterring what might in populations be seen as age-related functional decline.

It is useful to invoke a phenomenon that is well described in the biology of aging literature: homeostasis (Pedersen, Wan, and Mattson, 2001). This refers to the observation that older human beings (as well as older organisms in other species) may function at a normative level, but when a large stress occurs, whether a disease, illness or disorder, injury, or social occurrence, the ability, ceteris paribus, to return to one’s prior health and functional status is impaired when contrasted with that of younger adults. This may have import for older workers, who may be able to function under usual environmental circumstances, but who have more severe consequences after an acute medical insult, such as a given amount of trauma, a respiratory infection, a toxic exposure, or an unusual climatic condition. Thus, there may be some circumstances where older workers may require more enhanced protection from environmental insults than younger workers, because the consequences of those insults may be greater, and there may be greater premium placed on prevention. When a certain acute insult occurs in the face of existing, if controlled, chronic illness or disorder, the consequences may be more devastating. However, little research has been conducted in this area.

It is important to always consider the role of mental illness or disorder among older persons, including older workers. Mental conditions take a substantial toll on health status, and while major mental illnesses or disorders may have their onset in young adulthood, they often persist into old age. Mental illnesses or disorders such as various psychoses, major depression, bipolar disorder, and substance abuse often have important functional, social, and health consequences and can be related to workplace performance, absenteeism, and the risk workplace-related conditions. Pharmaceutical treatments of some of these conditions may also place some workers at increased risk of work-related injuries, but whether this is a special problem for older workers is uncertain.

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