Factors That Influence the Onset and Course of Disability

Disability is best seen as a function of the interaction of people’s physical capacity with demands presented by their life situation and a number of lifestyle, social, and environmental factors that influence their ability to perform a task. Technology also has an important impact on disability in many ways. This goes beyond the obvious benefits of assistive devices (hearing aids, glasses, hip replacements) and includes aspects of everyday life. As noted earlier, individuals who previously were considered disabled in terms of shopping, one of the traditional IADL measures, may now shop online and are thus no longer considered to have this disability. The built environment can also be important as the absence of stairs or the presence of elevators, ramps, or electric wheelchairs can dramatically improve mobility (Freedman et al., 2006; Crimmins and Beltrán-Sánchez, 2011). Lastly but important, social activity has been shown to have a “dose-dependent” favorable impact on the development of ADL or IADL disabilities (James et al., 2011).

Biomedical Factors

Biomedical factors independent of the disease process may increase or decrease the likelihood of disability at any given level of disease severity. For instance, individuals with lung disease or peripheral vascular disease will generally have their symptoms and disability increased if they smoke. And many initially obese patients with hip and knee arthritis find improvements with weight loss. Many obese patients seem to avoid heart disease despite the presence of biomedical risk factors like high blood pressure and high cholesterol as these factors are very commonly treated with effective pharmacologic agents (Martin, Schoeni, and Andreski, 2010).

The development of disability is a potentially reversible process. Clearly certain technologies such as hip or knee replacements or cataract removal promise dramatic reductions in disability, as do the less dramatic treatment of many diseases and many of the technologic, lifestyle, or environmental changes mentioned above. Such treatments can also increase the prevalence of disability in the population. For instance, changes in lifestyle (smoking, exercise) and improved treatment of risk factors (high blood pressure, high cholesterol) have decreased the incidence of stroke and, more recently, heart attack and some forms of cancer, reducing mortality and increasing survivorship and the prevalence of these disorders (Crimmins and Beltrán-Sánchez, 2011).

While it has been developing over several decades, the “obesity epidemic” (especially among certain racial and socioeconomic groups) has recently begun to attract widespread attention. Increases in weight beyond

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