Shift work is a necessity in an industrially developed country. Manufacturing, transportation, and health care rely on shift workers to maintain operations around the clock. A shift worker can be defined as someone who works evenings, nights, rotating shifts or extended shifts. Approximately 20% of people employed in the United States work in shifts [3]. Do these workers have any special problems that might be attributed to circadian disruption?

Unlike jet lag, which is usually a temporary disruption, shift work schedules and their disruptions can last for years. Humans are diurnal creatures (active during the day), and shift workers are often out of sync with environmental and social cues. Circadian adjustment to a new shift is gradual (taking a week or more), and changing to a new shift before adjustment is complete can cause perpetual desynchronization. Research shows that shift workers suffer from sleep disruption and fatigue, domestic disturbances, and health problems such as gastrointestinal disorders and increased risk of cardiovascular disease [3]. Task performance is also poorer at night [3]. The graph shows the probability of errors during shift work over a 24-hour period.

Certainly shift work is not going to be abandoned by modern society, but how can the circadian disruptions it causes be minimized? Many large companies employ consulting firms (such as Circadian Technologies, Inc.) to advise them on how to manage or prevent problems caused by shift work. The Center for Biological Timing is currently evaluating data from a major steel plant on the effects of the rate and direction of shift rotation on accident rates. Researchers hope to compare, for example, the number of accidents among workers who rotate from days to evenings to nights with those who rotate from nights back to days [21]. Other than adjusting schedules, "...implementing educational and support programs regarding biological rhythms, sleep, and family counseling may be a good way to improve the coping ability of shift workers" [3].