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There are many things we can blame for a bad night’s sleep – screen time, stress, too much booze. Now there is another culprit: the microbes in our gut.

We have long known that our microbiome has a powerful influence on our health, and new research is revealing that this extends to our sleep, too. But it is a complex, two-way relationship. “The microbiome is influencing sleep, and sleep is influencing the microbiome,” says at the University of Colorado Boulder. The good news is that there are ways we can intervene.

At first glance, the link between your stomach and sleeping patterns might not be obvious, but a growing number of studies are shedding light on the impact they have on each other. For instance, a 2023 study of 720 people found that was associated with better sleep. Likewise, a look at nearly 1000 people by researchers at King’s College London (KCL) and other institutions, in association with the personalised nutrition company Zoe, found that irregular sleep patterns were linked to associated with poorer health outcomes.

What’s more, changes in the composition of the gut microbiome are associated with several sleep conditions. Rapid eye movement sleep behaviour disorder, for instance, which causes sleepers to physically act out their dreams during REM sleep, is linked to a that produce the short-chain fatty acid butyrate and a rise in bacteria that increase inflammation.

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However, consistently involved with sleep health hasn’t proved possible. Teasing apart cause and effect is challenging too, especially when there are so many lifestyle factors that affect both sleep and our microbiome. In the Zoe-partnered study, for example, the people with the most irregular sleeping patterns – such as sleeping in at the weekend – also had the poorest quality diets, which could have had knock-on effects on the composition of their gut microbiome, rather than their microbiome causing their problematic sleep.

“Sleep impacts your dietary choices,” says at KCL, who worked on the study. “If you have a poor sleep, you make poorer dietary choices, and this will negatively impact the quality of your microbiome. It will reduce its diversity and change it to a less healthy composition.”

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Studies in animals can demonstrate some of the interactions between microbiome and sleep, and how they influence each other. In mice, depletion of the gut microbiota via long-term antibiotic treatment , while other studies in mice show that chronic sleep disruption . Even more interestingly, when faecal microbes from mice subjected to intermittent oxygen deprivation –mimicking symptoms of the condition obstructive sleep apnea, which is known to reduce sleep quality – are , the recipients develop disrupted, fragmented sleep.

These effects can result in a vicious cycle. For instance, studies in humans show that of people with the condition, which in turn exacerbates the symptoms.

But what is the mechanism? There are several routes of communication between our gut microbiome and the brain that could influence sleep. Bacteria can directly correspond with the brain via the vagus nerves, key information routes of the parasympathetic nervous system; they also release inflammatory chemicals that modulate the immune system; and they can produce hormones that affect our circadian rhythms, including sleep/wake cycles.

This all begs the question of whether we could improve our sleep by improving our microbiome. There are early hints that we can. Last year, a trial of 89 adults with poor sleep quality found that taking a probiotic supplement of the bacterium Bifidobacterium longum 1714 for eight weeks in subjective and objective assessments of their sleep quality compared with controls. This finding is in line with other research, such as a , which found that people taking one for at least four weeks had significantly better sleep quality than those who received a placebo.

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at the US National Institutes of Health says if we are looking to improve sleep, we might want to specifically target microbes that contribute to inflammation. She recommends eating foods rich in fibre, unsaturated fats and , as well as not eating too early or late, to improve the capacity of the microbiome to produce substances that enhance sleep quality. “The microbiome, with all its interactions with the immune system, hormones and stress hormones, has the potential to have a really large impact on sleep,” she says.