Night shifts and IBS: what the research found

Yes, there is a link, but it is narrower than the headlines suggest. A UK Biobank study followed 266,605 working adults for about nine years and found that people who always worked nights were more likely to be diagnosed with IBS than people who rarely or never did. It cannot show that nights cause IBS.

Do night shifts cause IBS?

Nobody has shown that they do. What we have is a clear association from one large study, and the people who wrote it are the first to say so: as an observational study, it “cannot establish a causal relationship between night shift work and IBS”. People who choose or end up on permanent nights may differ from day workers in ways nobody measured, and the authors list diet, occupation and psychosocial factors among the things that could still be muddying the picture.

That matters, because “nights give you IBS” and “people on permanent nights are diagnosed with IBS more often” are different sentences. Only the second one is on the evidence.

What did the UK Biobank study find?

UK Biobank recruited over half a million adults across England, Scotland and Wales between 2006 and 2010. This analysis, published in Frontiers in Public Health in 2025 by Lu and colleagues, took the 266,605 who were in work, had no IBS when they joined, and had answered two questions: does your work involve shift work, and if so, does it involve night shifts? Night shifts meant working through normal sleeping hours, such as midnight to 6am.

Over a median follow up of 9.03 years, 5,218 people were newly diagnosed with IBS. Diagnoses came from self report, GP records, hospital records and death records. Compared with people who never or rarely worked nights, people who always did had a higher risk in every version of the analysis. The fully adjusted hazard ratio, which allows for age, sex, sleep length, anxiety, depression, BMI, smoking and alcohol, was 1.36.

The raw numbers are worth seeing too. Of the 10,335 people who always worked nights, 227 were diagnosed during follow up. Of the 243,021 who never or rarely did, 4,775 were. In both groups, the great majority were never diagnosed with IBS at all.

Does it matter how often you work nights?

In this study, yes. Only the group who always worked nights showed the link. People who worked nights sometimes or usually did not have a significantly different risk from people who never or rarely did, which will interest anyone on a rotating rota.

Two more details are easy to miss. The link held across men and women, younger and older workers, short and long sleepers, and people with and without anxiety or depression. But when the researchers split people by weight, it only showed up in those with a BMI of 25 or more. In people with a BMI under 25, the result was not statistically significant. The authors call all of these subgroup findings exploratory, and so should we.

The study also could not say anything about years on nights. Shift work was asked about once, at the start, so someone who left nights in 2011 sits in the same group as someone still doing them now.

Is there research on nurses specifically?

There is, and it is smaller. Nojkov and colleagues surveyed 399 nurses at a university hospital in Michigan in 2010 using the Rome III questionnaire for IBS.

The two studies disagree on who carries the risk. The UK one points at permanent nights and the American one at rotating shifts. Neither can settle it, and the honest reading is that shift patterns and gut symptoms travel together more often than chance would suggest, with the details still open.

Why might nights upset your gut?

Nobody knows for certain. The UK Biobank authors suggest that a disrupted body clock may upset the gut’s bacteria and its movement, and that the eating patterns of shift work, more high fat and high sugar food at irregular times, may add to it. Those are hypotheses, not findings from their data. The British Dietetic Association’s resource on shift work notes that some studies suggest a higher incidence of gastrointestinal disorders in shift workers, alongside other problems.

The exact cause of IBS itself is unknown. It has been linked to food moving through the gut too quickly or too slowly, a gut that is oversensitive, stress, a previous bout of gastroenteritis and family history. A run of nights brings plenty of stress, for a start.

I went to a doctor once with stomach pains I could not ignore, straight off a night shift and due back that night. My gut was growling and I could feel it spasming under my hand. The doctor listened to my stomach for a minute, said IBS, and prescribed antispasmodics. There were no questions about my diet. I’d like you to have that conversation even if your doctor doesn’t start it.

What can you do if you work nights and your gut is struggling?

Start with the things a ward makes hard. Ignoring the urge to go and not drinking enough are both common causes of constipation, and so is changing your daily routine, which is the definition of a run of nights. Keep a bottle where you will walk past it, and go when you need to, not when the corridor is quiet.

How you eat across the night is the next lever. I’ve set out the timings, from the main meal before you leave to the snack in the small hours, in what to eat on a night shift, and the days afterwards in coming off nights. If tiredness is the bigger problem than your gut, the afternoon crash quiz will help you work out what is behind it.

None of this means your symptoms are IBS. A study about thousands of people cannot tell you what is going on in your own gut. That needs a GP.

When should you see a GP?

The NHS says to see a GP if you think you might have IBS and have had symptoms for over 4 weeks. Write down what you have noticed first; there is a guide to what to tell your GP about gut symptoms.

Ask for an urgent GP appointment or get help from NHS 111 if you:

• have lost a lot of weight for no reason
• are bleeding from your bottom or have bloody diarrhoea
• find a hard lump or swelling in your tummy
• have shortness of breath, noticeable heartbeats (palpitations) and skin that’s paler than usual

Do not wait for your next set of days off for any of those.