Is working at night unhealthy? How late shifts can affect sleep and trigger diabetes

Unhealthy habits associated with working late or night shifts can induce cancer, the WHO says, and make other health conditions more likely

Many people, from drivers to doctors, work in shifts. Some start early in the morning, others at midday. Some work at night while everyone else is asleep.

Working at night is particularly challenging for the body because it goes against our natural rhythms. How does a person get used to it?

Specialists provide some helpful advice.

Do you have questions about the biggest topics and trends from around the world? Get the answers with SCMP Knowledge, our new platform of curated content with explainers, FAQs, analyses and infographics brought to you by our award-winning team.

How does shift and night work affect our bodies?

Many of our bodily functions shut down at night. Our body temperature drops and our pulse, digestive system and breathing slow down.

"Your body wants to rest and relax, so working against the circadian rhythm (the body's natural 24-hour cycle) is always associated with greater effort," says Frank Brenscheidt from Germany's Federal Institute for Occupational Safety and Health.

Sleeping during the day is not as restorative as it is at night. You can only get used to night work to a limited extent. Your body cannot be completely reprogrammed, he says.

Working against your natural rhythm can have a serious impact on your health.

"There is an increased risk of type 2 diabetes, cardiovascular disease, ischemic stroke, mental illness and miscarriages," says Andrea Rodenbeck, a chronobiologist - who studies the body's biological rhythms - and sleep researcher in Germany.

Night work can be carcinogenic, meaning it can cause cancer, the International Agency for Research on Cancer of the World Health Organization found in a 2019 evaluation.

Unhealthy habits associated with shift work may contribute to this - drinking alcohol that you believe helps you relax better after work, or eating junk food in a hurry. Your social life often suffers too, and so can your psyche.

How does night work affect people's sleep?

"On average, there is no difference in sleep duration in a three-shift model," says sleep researcher Rodenbeck. "But there are significant differences between the shift types."

After a night shift, many employees often get less than six hours of sleep. Sleep-related breathing disorders are also observed more frequently after night shifts.

Who is suited for shift work and who is not?

An individual's ability to adapt to shift work depends heavily on their internal clock. People with an "owl" chronotype, who are naturally more productive in the evening, find night work easier.

"Larks", on the other hand - people who get up early and get tired early - have greater difficulties.

Age also plays a role.

"The younger you are, the later your internal rhythm is, which is why younger people cope better with late and night shifts and older people with early shifts," says Rodenbeck.

People's ability to adapt to rotating shifts often decreases with age, says Brenscheidt. This has been shown in studies with police officers "who start their working lives in very good physical condition, but after 20 years, a considerable number of them develop health problems".

What should shift schedules look like?

There are clear recommendations for scheduling alternating shifts. Forward-rotating shifts - early shift followed by late shift and then night shift - are more tolerable than the reverse order, says Brenscheidt. "And night shifts should not be longer than eight hours."

Reliable schedules are crucial. "Time off must actually be time off," he says.

Also, each shift phase should only last a few days, preferably just two days of night shifts in a row instead of a whole week. "Then it's less difficult to switch back to a different rhythm," says Brenscheidt.

Shorter working hours also make shift work more tolerable. "If possible, people who work shifts should work less than 40 hours a week."

How can you organise changing working hours?

Shift workers face a double challenge: they have a more strenuous work rhythm and also have to be more disciplined to stay healthy.

"Good sleep hygiene is important," says Brenscheidt. "It's best to make a sleep schedule in addition to your shift plan."

After a night shift, you should not use the following day for appointments, but rest. Taking a further nap in the afternoon before your shift can help prevent tiredness at work.

Nutrition is important. If you eat at night, your digestion and metabolism are out of sync because they would normally be in rest mode. So it is better not to overload your stomach and intestines with heavy meals.

The German Nutrition Society recommends a balanced dinner before the night shift, for example, and lighter snacks such as vegetable soups, sandwiches or wraps during work breaks.

If possible, only eat your food before midnight, and then only again at the end of your shift. Avoid alcohol and nicotine.

Shift workers must also pay heed to their social rhythm, as family and friends often live to a completely different beat. Consciously planning joint activities can help. And don't forget hobbies - Brenscheidt cites sport - "which also help to reduce stress".

Like what you read? Follow SCMP Lifestyle on Facebook, X and Instagram. You can also sign up for our eNewsletter here.

More Articles from SCMP

This article originally appeared on the South China Morning Post (www.scmp.com), the leading news media reporting on China and Asia.

Copyright (c) 2025. South China Morning Post Publishers Ltd. All rights reserved.