Night workers often experience a circadian 'trough' of decreased alertness during their shifts. This occurs between midnight, when cortisol levels are lowest, and 4.00 am, when core body temperature is at its lowest
Sleep deprivation
Tilley and
Wilkinson (1982)
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Daytime sleep is typically between 1 and 2 hours shorter than a nocturnal sleep period. REM is particularly affected. This is because of interruptions such as noises outside
Effects on health
Knutsson et al. (1986)
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Found that individuals who worked shifts for more than 15 years were 3 times more likely to develop heart disease than non-shift workers
Martino et al. (2008)
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Linked shift work to kidney disease. This may be due to the direct effects of desynchronisation or indirect effects such as sleep disruption
Other effects
Solomon (1993)
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Divorce rates can be as high as 60% among all night-shift workers
Reducing harmful effects
Rotating shifts
Gold et al. (1992)
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Research indicates that more problems occur when people have to do rotating shifts
Forward-rotating shifts
Bambra et al. (2008)
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Follow the logical order of the day (phase delay) and it may be easier on the body and less damaging to health
Artificial lighting
Gronfier et al. (2007)
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Were able to entrain circadian rhythms to longer than 24 hours just by using bright light pulses
Jet lag
Performance decrement
Recht et al. (1995)
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Analysed US baseball results over a 3 year period. Teams that travelled east-west won on average 44% of their games, whereas when travelling west-east the percentage dropped to 37%
Loss of appetite
Nausea
Disorientation
Reducing harmful effects
Melatonin
Herxheimer and
Petrie (2001)
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Reviewed 10 studies and found that where melatonin was taken near to bed-time, it was remarkably effective
Social customs
Fuller et al. (2008)
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When travelling, it helps to eat at the right time and got to sleep when the clock says it's time to go to sleep. This research suggests that a period of fasting followed by eating on the new time schedule should help entrain biological rhythms