Working nights isn’t easy. Your sleep’s all over the place, your meals are at odd hours, and it can leave you feeling out of sync with everyone else. But there’s another concern that doesn’t get talked about enough: cancer risk.

For years the research has been a bit mixed, but newer studies are painting a clearer picture. Long-term night work, especially when it’s regular, does seem to raise the risk of certain cancers.

In this post, I’ll break down what the science actually says, which cancers are linked, how many years on nights matter most, and what you can do to protect your health if night shifts are part of your life.

Summary

• Long-term, regular night work can cause breast cancer in women and may also raise the risk of prostate cancer in men.
• The risk builds with time – the more years and the more frequent the shifts, the higher the concern.
• Night work disrupts your body clock, lowers melatonin (the “sleep hormone”), and can affect hormones and inflammation in ways that may promote cancer.
• You can support your health by protecting your sleep, managing light exposure, eating at sensible times, and keeping your lifestyle as balanced as you can.

So… is night-shift work really carcinogenic?

Yes. In 2025, the U.S. National Toxicology Program (NTP) reviewed all the evidence and concluded that persistent night-shift work can cause breast cancer in women and may cause prostate cancer in men. This is the strongest statement we’ve seen so far.

The World Health Organization’s cancer agency (IARC) also lists night-shift work as “probably carcinogenic”. In plain words, it means night shifts can raise cancer risk, but it doesn’t happen to everyone.

Think of it like this: the hazard is there, but the actual risk depends on how often and how long you work nights, plus your overall health and lifestyle.

Which cancers are linked to night work?

The NTP’s conclusion wasn’t pulled out of thin air – it came from years of research pointing to certain cancers more than others. Here’s what studies have found:

Breast cancer (strongest link)
This is where the clearest pattern shows up. The longer and more often women work nights (especially if they start young) the higher the risk. One large analysis found it creeps up over time: about 4% higher after 10 years, 9% after 20, and 13% after 30 years of regular night shifts.

Prostate cancer (possible, but less certain)
Some studies suggest the risk climbs with more years on nights – around 12% at 10 years, 24% at 20, and nearly 40% at 30 years. But others don’t find much of a link, so this one’s still under debate.

Rectal cancer (a late signal)
Overall bowel cancer isn’t strongly linked to shift work, but rectal cancer does show up in some studies, particularly after 15 years or more of rotating night shifts.

Other cancers have been studied too, but the evidence isn’t strong enough yet to say for sure.

When does night work become a real concern?

Not all night-shift work carries the same risk. What matters most is how often you do it and for how many years.

Research shows the risk really starts to stand out with regular night shifts over long periods of time. For example:

• Working three or more nights a week for at least 10 years has been linked to higher breast cancer risk.
• Women who started night shifts at a younger age and kept going for 20 years or more showed some of the biggest increases in risk.
• For rectal cancer, the clearest signal appeared after 15 years or more of rotating night shifts.

Short-term or occasional night work doesn’t seem to carry the same level of risk in the big studies. It’s the long, steady exposure that adds up over time.

Why does night work raise cancer risk?

Scientists don’t have every answer yet, but there are a few clear ways night shifts can affect the body:

Body clock disruption
Your body runs on a 24-hour rhythm (called the circadian rhythm). Night work throws this rhythm out of sync, which can affect how cells repair and grow.

Less melatonin
Melatonin is known as the “sleep hormone,” but it also helps protect cells from damage. Normally, it rises in the dark and drops in the light. Night shifts mean you’re exposed to light when your body expects darkness, which lowers melatonin. Some studies suggest this loss of melatonin protection may speed up cancer cell growth.

Hormone changes
Night work can alter levels of hormones like oestrogen and insulin. These play a role in how cells divide, how your metabolism works, and even how your weight changes over time.

Inflammation and immunity
Odd sleep patterns and poor rest can lead to low-grade inflammation and changes in immune function, both of which can influence cancer risk.

Animal and lab studies back this up too. For example, tumours in some experiments grew faster when animals were exposed to light at night, but slowed down when melatonin was added back.

What can you do if you have to work nights?

Night shifts put a lot of pressure on your body. You can’t always change your schedule, but you can make choices that help reduce the strain and keep you healthier in the long run.

Light matters
Your body clock depends on light. Try to keep your bedroom as dark as possible when you sleep – blackout curtains or an eye mask are worth it. On the way home, sunglasses can help signal to your brain that it’s “night.” At work, keep the lights bright enough to stay alert, but avoid blasting yourself with extra-bright light if you don’t need it.

Prioritise sleep
Your body needs good-quality rest to recover from nights. Aim for a cool, dark, and quiet room and try to get as much sleep in one stretch as you can, but if that’s tough, short naps can help top you up.

Food and drink choices
Try to eat your main meal before your shift starts. Keep snacks light at night – fruit, nuts, yoghurt – instead of heavy, greasy meals that mess with digestion. Caffeine is fine, but use it early in your shift only. Too late and it’ll wreck your sleep.

Stay active
Even short walks or light exercise can help your mood, lower stress, and keep inflammation down. It doesn’t have to be a full workout – small daily movement adds up.

Get workplace support
You don’t have to figure this all out alone. Sometimes small changes to shift patterns, lighting, or break times can ease the strain on your body. This is where occupational medicine can really help – they work with employers and employees to make night shifts safer and support your long-term health.

What about supplements?

Night shifts can leave your body stressed, run down, and low on energy. Supplements won’t erase the risks of night work, but they can give your body extra support:

• Vitamin D – top priority in winter, since you’re missing daylight. It supports your immune system and overall health.
• Vitamin C – stress can burn through your vitamin C stores more quickly. A supplement can give your immune system a boost.
• B-complex – these vitamins are important for energy and reducing fatigue. Many night workers find them helpful when exhaustion builds up.
• Magnesium – can support relaxation and better sleep quality, especially if your sleep schedule is unpredictable.

That said, supplements are not a substitute for a good diet. Start with plenty of fruit, veg, whole foods, and healthy fats. Think of supplements as a backup – extra fuel when your body is under pressure.

FAQs about night shifts and cancer

Is occasional night work risky?
The biggest concern is with long-term, regular night shifts. A few nights here and there isn’t the same as working them for years.

Are rotating shifts worse than fixed ones?
Yes, rotating shifts seem harder on the body clock because you’re constantly changing schedules. Studies show cancer risk is more noticeable in people who worked rotating nights for many years.

If I stop working nights, does my risk go down?
It looks like it does. The longer you’ve been off nights, the more your body clock can recover. That’s another reason to focus on sleep, light, and overall health even if you’re still working shifts now.

The bottom line

Night shifts are a reality for many people, but they do come with health risks. The latest research shows long-term night work can raise the risk of certain cancers, especially breast cancer, with possible links to prostate and rectal cancer too. The longer and more often you work nights, the more that risk builds.

That doesn’t mean cancer is guaranteed. What it does mean is that looking after yourself matters even more. Protect your sleep, manage your light exposure, eat well, move your body, and consider smart supplements like vitamin D in winter.

You may not be able to change your job, but you can give your body the best tools to stay strong and healthy.