Shiftwork and the older worker.

The number of workers employed on shiftwork is large, and it appears to be increasing. The impact of shiftwork on the occupational safety and health of workers is complex and involves both biological and behavioral variables. Current conceptual models propose that the impact of shiftwork, where night work is involved, increases with exposure. At some point the worker is said to reach a tolerance limit beyond which shiftwork is no longer safe. Sleep variables have proven to be sensitive markers for the effects of night shiftwork. Data from U.S. workers show a statistically significant interaction among age, gender, and shift for the workday sleep length of workers on permanent day, afternoon/evening, and night shifts. Sleep length declines with age for both male and female night workers, as well as for male workers on afternoon/evening shifts. In addition, female night workers in the 18-49 age range sleep significantly less than same-age male night workers. Nap behavior also varies with shift, but age and gender effects do not appear to account for the variance. The results support the assumption that most night shiftworkers are at risk even though they often give the appearance of being able to tolerate nocturnal work hours. However, it is not yet clear how age and gender are related to the social, circadian, and environmental factors that influence the sleep length of shiftworkers.