What night shifts do to a body built for days.
Your body clock expects sleep at night and never fully adjusts to working through it. What that does to sleep, digestion and alertness, and the habits that help, hour by hour, from the UK Health and Safety Executive's guidance.
Metro drivers at Kropotkinskaya station, Moscow, on the night of the metro's 76th anniversary, 15 May 2011, 03:24. Photo: Mikhail (Vokabre) Shcherbakov, CC BY-SA 2.0.
_(5944345510).jpg){kind=link}
Your body runs on a daily clock set by daylight.
A clock in the brain sets the daily cycle of hormones and body activity, and daylight, meal times and working hours keep it in step with the world. At night heart rate, blood pressure and body temperature fall, and we slow down and feel sleepy.
The clock resists abrupt changes. After a few night shifts it starts to shift, but each function at its own pace, so digestion, alertness and sleep are disturbed. It never fully adjusts, even on permanent nights, and it pulls back towards daylight on days off.
Health and Safety Executive, Managing shift work (HSG256), paragraphs 19 to 21 (2006)- 2017A Nobel Prize for discovering the molecular mechanisms that control the circadian rhythm.NobelPrize.org, The Nobel Prize in Physiology or Medicine (2017)
- Days or weeksFor the clock to adjust to an abrupt change in when you sleep and wake.Health and Safety Executive, Managing shift work (HSG256), paragraph 21 (2006)
- Never fullyEven for workers on permanent night shifts.Health and Safety Executive, Managing shift work (HSG256), paragraph 21 (2006)
What shift work can do.
Shifts outside daytime hours, especially nights and early starts, can bring:
- a disrupted body clock;
- fatigue;
- difficulty sleeping;
- disturbed appetite and digestion;
- reliance on sedatives or stimulants;
- social and domestic problems.
Over the long term, there is some evidence linking shift work with digestive problems such as indigestion and ulcers, with heart problems such as high blood pressure and coronary heart disease, and with catching more colds, flu and stomach bugs. Shift work may also make diabetes, asthma, epilepsy and psychiatric illness worse.
Health and Safety Executive, Managing shift work (HSG256), paragraphs 35 and 37 (2006)Sleep a little before your first night, and move a little before you start.
- Have a short sleep before your first night shift.
- Take moderate exercise before starting work: it may make you more alert during the shift.
- On regular shifts, try different bedtimes, for example soon after you get home, or staying up and sleeping before the next shift, then keep to the schedule that suits you.
Eat light and often, and keep drinking.
- Light meals
- Easy to digest
- Fruit, not sweets
- Plenty to drink
Regular light meals or snacks are less likely to make you drowsy than one heavy meal. Pasta, rice, bread, salad, fruit, vegetables and milk products are easy to digest; fatty, spicy or heavy meals are not, and can make you drowsy just when you need to be alert. Sugary foods such as chocolate give a short boost, then a dip. Drink plenty, since dehydration lowers both mental and physical performance, but not too much just before you sleep.
Health and Safety Executive, Managing shift work (HSG256), appendix 2, paragraph 5 (2006)Keep the light bright and keep moving.
- Bright light
- Short breaks
- Walk around
- Talk to colleagues
Take regular short breaks if you can, and get up and walk around during them. Plan more stimulating work for the times you feel most drowsy, and keep in contact with co-workers: it helps both of you stay alert.
Caffeine improves reaction time and alertness for short periods. Use it occasionally rather than relying on it, and think about what happens when it wears off, at the wheel for example.
Health and Safety Executive, Managing shift work (HSG256), appendix 2, paragraphs 6 and 9 (2006)The drive home
Compared with day workers, night workers are more likely to have an accident driving home from work. What helps:
- public transport or a taxi rather than driving;
- a little exercise before the journey;
- sharing the driving, and not hurrying;
- stopping if you feel sleepy, and taking a short nap where it is safe.
Sleeping in daylight
Day sleep is usually lighter and shorter, more often disturbed by warmth and noise, and bright light at dawn can make it harder to fall asleep. Most adults need 7 to 8 hours of sleep a day; if you cannot get them, resting still helps.
- Darken the bedroom with heavy curtains, blackout blinds or eye shades.
- Keep it cool: cool conditions improve sleep.
- Turn the phone down, and ask your household and close neighbours to keep the noise down.
- Mask outside noise with earplugs, white noise or background music.
- Wind down as you would before a normal night. Avoid vigorous exercise, caffeine in the hours before bed, alcohol and heavy meals; a light snack is fine.
Coming off nights.
Coming off night shifts, have a short sleep and go to bed earlier that night. Switching back to a daytime routine on rest days keeps the body clock unsettled, as it tries to reset to daylight.
Missing sleep builds a sleep debt, and the urge to pay it back can be very hard to resist. Alcohol may help you fall asleep but brings earlier waking and poorer sleep, and regular sleeping pills are not recommended because they can lead to dependency.
Shifts out of step with family and friends can leave you isolated. Share your rota so they can plan around it, keep meal times, evenings and weekends together where you can, and fit chores around your sleep rather than the other way round.
Health and Safety Executive, Managing shift work (HSG256), paragraphs 21 and 24, appendix 2, paragraphs 2, 6 and 8 (2006); Health and Safety Executive, Hints and tips for shift-workers (read 15 October 2026)Night shift work is probably carcinogenic to humans.
In June 2019, 27 experts from 16 countries met in Lyon for the International Agency for Research on Cancer, the World Health Organization's cancer agency, and placed night shift work in Group 2A: probably carcinogenic to humans.
The evidence in humans is limited: studies have found positive associations with cancers of the breast, prostate, colon and rectum. The evidence in experimental animals is sufficient and the mechanistic evidence strong. The classification measures how strong the evidence is that night shift work can cause cancer, not how large the risk is. The agency does not give individual advice; if you are worried about your health, it suggests asking your doctor.
IARC, Monographs meeting 124, questions and answers (5 July 2019); IARC Monographs, volume 124: Night shift work (2020)