and metabolism of environmental agents. In the experimental setting, there may be age-related declines in rodent xenobiotic metabolism (Williams and Woodhouse, 1996), including the hydroxylation of benzene, possibly due to age-related changes in xenobiotic action on liver microsomes (Sukhodub and Padalko, 1999). Cigarette smoke has an age-related differential effect on pulmonary xenobiotic metabolizing enzymes (Eke, Vural, and Iscan, 1997).

Immunity

Aging is associated with general changes in immune function, although the relation of these changes to disease occurrence and survival is uncertain (Meyer, 2001), and more research is needed. An example from animal experimentation is the observation that exposure to certain immuno-suppressive xenobiotics leads to greater T. spirilas infection rates among older than younger animals (Leubke, Copeland, and Andrews, 2000). It is possible that these age-related changes impair responses to vaccines, leading to lesser protection from preventable infections (Ginaldi et al., 2001). It is possible that infection risk is altered by overtly nonimmune mechanisms—there is evidence that metal fume exposure may alter the risk of community-acquired pneumonia (Palmer et al., 2003). These observations have two immediate implications for the older worker. One is the possibly increased risk of clinical infections and the need for clinical prevention to maintain worker health. The other is the potential for increased infection risk among older workers exposed to special biological agents in the work environment. An additional potential implication is that the altered immune function among older workers may diminish the response to and protection by various vaccines (Murasko et al., 2002). Much more research is needed in this area.

Thermoregulation

Age-related changes in thermoregulatory function may be important for older workers. Older people have seasonally higher mortality rates at both high and low extremes of temperatures. Older persons, particularly those over 60 years, have a lower capacity to maintain core temperature during a cold challenge and have a reduced thermal sensitivity and a reduced thermal perception during cooling (Smolander, 2002). Thermogenesis under situations of cold stress appears to decline with age (Florez-Duquet and McDonald, 1998). Similarly, reflex sweating to heat exposure may be diminished in older persons, making them more heat sensitive, and mechanisms for this have been suggested (Holowatz et al., 2003). Whether these phenomena are important for actual job exposures to temperature extremes should be further evaluated. Worker selection factors and the modulation



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