Shift work: health, performance and safety problems, traditional countermeasures, and innovative management strategies to reduce circadian misalignment

Abstract

There are three mechanisms that may contribute to the health, performance, and safety problems associated with night-shift work: (1) circadian misalignment between the internal circadian clock and activities such as work, sleep, and eating, (2) chronic, partial sleep deprivation, and (3) melatonin suppression by light at night. The typical countermeasures, such as caffeine, naps, and melatonin (for its sleep-promoting effect), along with education about sleep and circadian rhythms, are the components of most fatigue risk-management plans. We contend that these, while better than nothing, are not enough because they do not address the underlying cause of the problems, which is circadian misalignment. We explain how to reset (phase-shift) the circadian clock to partially align with the night-work, day-sleep schedule, and thus reduce circadian misalignment while preserving sleep and functioning on days off. This involves controlling light and dark using outdoor light exposure, sunglasses, sleep in the dark, and a little bright light during night work. We present a diagram of a sleep-and-light schedule to reduce circadian misalignment in permanent night work, or a rotation between evenings and nights, and give practical advice on how to implement this type of plan.

Phase advancing human circadian rhythms with morning bright light, afternoon melatonin, and gradually shifted sleep: can we reduce morning bright-light duration?

“…Misalignment between the circadian clock and 24-hour rhythmic behaviors, like sleep/wake and fasting/feeding (“circadian misalignment”) is associated with sleep disruption, excessive sleepiness and cognitive decrements during wake, and gastrointestinal problems [1–12]. The most recognized cause of circadian misalignment is jet lag after crossing multiple time zones, though night shift work and early school or work times are other situations in which individuals can experience circadian misalignment.…”

“…Appropriately timed sleep (dark), light, and exogenous melatonin can phase shift circadian rhythms, and therefore can be used to reduce the degree of circadian misalignment and attenuate risks for negative health and daily functioning outcomes [7, 11, 12]. The direction and magnitude of the shift is predicted by phase response curves (PRCs) [19–29].…”

Individually tailored light intervention through closed eyelids to promote circadian alignment and sleep health

“…When this pattern is disrupted or misaligned with social requirements, a tailored light intervention can be used to promote sleep consolidation and efficiency by aligning the signals from the biological clock with the sleep drive mechanism, thus controlling the timing of the sleep/wake cycle (4). The relationship between the timing of a light intervention and the changes (magnitude and direction) in circadian time is described by a phase response curve (PRC) (5).…”

Circadian rhythms of European and African-Americans after a large delay of sleep as in jet lag and night work

“…Jet travel and night work result in a large change in the time for sleep and wake, a large phase shift, producing circadian misalignment between sleep, work, meals and the internal circadian rhythms. Circadian misalignment leads to a myriad of health, safety and productivity problems1234567891011121314.…”

“…Jet lag can be reduced or eliminated by phase-shifting circadian rhythms to the new time zone before the flight and/or speeding up the phase shifting of circadian rhythms after the flight79. Night work could be made safer and healthier and daytime sleep could be lengthened and improved by shifting circadian rhythms to align, at least partially, with daytime sleep815. In two laboratory studies we carefully timed bright light to advance (shift earlier in time)16 or delay (shift later in time)17 circadian rhythms, by determining the circadian phase of each individual so that the bright light could be applied at the same circadian phase in all subjects.…”