Shift-work and Sleep
Shift-work can be defined as work that tends to occur outside the traditional working day, usually in the hours of 7pm to 6am. Shift-work schedules can take place exclusively in the usual sleep period, occur as early morning shifts (e.g. starting at say 4-6am), or be variable (rotating) on a day-to-day or weekly basis. All three patterns may lead to sleep disturbances and impaired daytime functioning due to:
(1) Attempting to initiate sleep at a time that is inconsistent with our internal biological clock (e.g. during daylight hours)
(2) Inconsistent bed and rise times due to changing, variable shifts, including weekday versus weekend patterns.
Our biological clock has developed throughout evolution to accommodate sleep at night (when light levels are low) and maintain wakefulness and alertness during the main daylight period. Often those who work night-shifts will have difficulties sleeping during the day, after a shift, and will commonly have reduced total sleep time (sometimes by up to four hours!) and poorer sleep quality. Such workers may also feel intense sleepiness during night-shifts, due to our internal clock sending out a reduced alertness signal (after all, this is when most people are asleep). In extreme cases this excessive sleepiness may lead to occupational injury or accident.
Whilst some workers adjust well to shift work, as a group those who work shifts tend to experience greater levels of sleep disturbance, fatigue, work-related accidents, cardiovascular, gastrointestinal problems and, in women, breast cancer. Disruption of the natural circadian rhythm due to light exposure at night, and resultant impairments to sleep, are thought to contribute to the higher prevalence of ill-health in shift-workers. Environmental factors like noise and social obligations may also make sleep during the daytime very difficult.
Treatment of sleep disturbances due to shift-work focus on optimizing the adaptation to the new shift pattern so that alertness is maintained during the scheduled shift and that sleep can take place during the day. For example, work has shown that exposure to bright light prior to or during the night-shift period can help one's internal clock adapt and 're-set', permitting sleep to happen in a block later in the day. Avoiding light during the early morning (e.g. on the way home from a night-shift) may also help with this. Other recommendations may be to schedule planned naps prior to starting a night-shift, to alleviate any sleep debt, as well as to use stimulants (such as caffeine) to help maintain alertness during the shift.