prior ones (Manton, Corder, and Stallard, 1997; Schoeni, Freedman, and Wallace, 2001; Freedman, Aykan, and Martin, 2001). The issue is complex and sometimes disputed. However, if true, general, and persistent, this trend could have a positive impact on the net health and function of older workers and their responses to workplace challenges.
In general, almost all physiological and mental functions change with increasing age, even if at varying rates and intensities, including internal organ function, physical movement, and sense organ functional characteristics. However, as noted above, the causes for these changes are often unclear, and the consequences for complex activities such as individual job performance are even more uncertain because of personal adaptations and selective forces over time. Nor is it clear how many of the measurable changes are preventable or modifiable, but an increasing literature on intervention studies suggests that some mutability is possible.
When objectively evaluating and measuring the function and performance of older workers, several observations pertinent to assessing age-related physiological and metabolic changes should be considered in order to understand the impact of past or present work exposures on health and functional status:
While the rates of age-related change are highly variable by organ, organ system, and anatomic region, in general the slope declines at a greater rate with increasing age. Thus, an important research and clinical problem is that older workers may need more frequent assessments to characterize the impact of work-related exposures. Also, it should be noted that many studies infer age-related change from cross-sectional population measurement, an inference that may not always reflect the reality or trajectory of longitudinal change (for example, see Louis et al., 1986).
Age-related changes in workplace performance, particularly using job-related production measures, may not be due to age-related anatomic or physiological changes alone. Rather, there may be other social and psychological factors that impinge more prominently on that performance, such as caregiving chores, altered motivation, and social discord among workers. At least potentially, this may also be true of even more abstract physiological assessments. For example, the impact of social stress on immune function is well documented (Kiecolt-Glaser et al., 2002).
There may be great differences between subtle physiological measures of organs and organ systems and their effects on complex human performance. It is often uncertain whether physiological or biochemical