Sleepless nights? Your gut might be to blame

Gut health can impact everything from mental health to the immune system—and it could be behind poor sleep too.

Specific types of gut bacteria have now been linked to insomnia risk by researchers from The Affiliated Brain Hospital of Nanjing Medical University in China.

The team found that certain types of bacteria seem to boost or lower the risk of the sleep condition, while insomnia itself may in turn also alter the abundance of certain gut ‘bugs’.

It is estimated that 12 percent of people in the U.S. have been diagnosed with chronic insomnia, according to the American Academy of Sleep Medicine.

Insomnia involves difficulty falling asleep, waking up during the night, lying awake at night and waking up too early—all of which come with daytime symptoms of tiredness and irritability too.

While previous studies have explored the effects of the gut microbiome on various sleep characteristics, it is not clear how different groups of gut bacteria might affect the risk of insomnia.

The researchers explored data on 386,533 people with insomnia from a previously published genome-wide analysis study, gut microbiome data for 18,340 people from the MiBioGen alliance and for 8,208 people from the Dutch Microbiome Project with (71 groups of bacteria in common).

Their analysis revealed associations between specific gut microbes and insomnia. Overall, a total of 14 groups of bacteria were positively associated with insomnia (1–4 percent higher odds) and eight groups showed a negative association (1–3 percent lower odds.)

Insomnia itself was associated with a reduction of between 43 percent and 79 percent in the abundance of seven groups of bacteria and a 65 percent to a more than fourfold increase in the abundance of 12 other groups.

The Odoribacter class of bacteria, in particular, was significantly associated with the risk of insomnia, the team reported.

“Odoribacter plays a role in producing short-chain fatty acids like butyrate, which influence inflammation, neurotransmitter balance and circadian regulation,” gastroenterologist Lindsey Ann Edwards of King’s College London—who was not involved in the present study—told Newsweek.

“Interestingly, its effects aren’t universally ‘good’ or ‘bad’—it has been shown to have positive or negative impacts depending on the disease in question. Its influence also depends heavily on an individual’s overall microbiome composition, because gut bacteria interact as a community.

“Through a process called metabolic cross-feeding, one species’ waste products can serve as another’s fuel, meaning the broader microbial network often determines whether Odoribacter’s presence is helpful or harmful.”

The researchers note that no pleiotropy—the production by a single gene of two or more apparently unrelated effects—was identified, strengthening the integrity of the findings and implying causation.

“It’s a fascinating and promising line of research. The link between gut microbiota and sleep is still emerging, and this study adds another important piece to the puzzle,” Edwards said.

“While it’s still early days, the fact that they’ve identified potential causal relationships makes the findings especially interesting. That said, the results need to be interpreted with caution until confirmed by larger, randomized controlled trials.”

The study authors said limitations include all participants being of European descent (and the makeup of the microbiome varying among different ethnicities and geographies). Factors like diet and lifestyle, known to affect the microbiome and the interplay between genes and the environment, also weren’t accounted for.

Edwards explained that while bacteria are linked to insomnia, those same bacteria may themselves be shaped by a person’s eating habits, stress levels, and environment.

“Diet is one of the strongest influences we know of; for example, the types of fibre and plant diversity in the diet can shift bacterial populations sometimes even within days,” Dr. Emily Prpa—a registered nutritionist at Yakult who was also not involved in the study—told Newsweek.

“Lifestyle factors such as exercise and alcohol intake also play a role, as do environmental exposures like pollution, medications, social life and geography. Genetics influences the microbiome too, though to a smaller degree than lifestyle. One big omission in this study is stress—it’s both a known disruptor of sleep and a factor that can significantly alter the gut microbiome via the gut–brain axis.”

The researchers concluded that the intertwined effects of insomnia on gut microbiota, and vice versa, represent a complex relationship involving immune regulation, inflammatory response and the release of neurotransmitters, as well as other molecular and cellular pathways.

“Our study offers preliminary evidence supporting a causal effect between insomnia and gut microbiota, providing valuable insights for the future development of microbiome-inspired treatment plans for insomnia,” the researchers explained in a statement.

These could include the use of probiotics, prebiotics, or fecal microbiota transplantation (FMT, transferring healthy gut bacteria via a donor’s stool), they said.

“In theory—probiotics, prebiotics or FMT could introduce or encourage beneficial bacteria. However, gut ecosystems are complex,” Edwards emphasized.

“Simply adding ‘good’ bacteria doesn’t guarantee they’ll establish themselves or outcompete the ‘bad’ ones, especially if the underlying causes (like poor diet or chronic stress) remain. Success would likely require a combination of targeted bacteria plus supportive diet and lifestyle changes.”

Edwards said the next step in this field of research should be well-designed randomized controlled trials to confirm whether modifying gut bacteria can directly improve insomnia symptoms.

Do you have a tip on a health story that Newsweek should be covering? Do you have a question about gut health and sleep? Let us know via health@newsweek.com.

Reference

Jansen, P. R., Watanabe, K., Stringer, S., Skene, N., Bryois, J., Hammerschlag, A. R., de Leeuw, C. A., Benjamins, J. S., Muñoz-Manchado, A. B., Nagel, M., Savage, J. E., Tiemeier, H., White, T., Tung, J. Y., Hinds, D. A., Vacic, V., Wang, X., Sullivan, P. F., van der Sluis, S., … Posthuma, D. (2019). Genome-wide analysis of insomnia in 1,331,010 individuals identifies new risk loci and functional pathways. Nature Genetics, 51(3), 394–403. https://doi.org/10.1038/s41588-018-0333-3

Shi, S., Liu, D., Baranova, A., Cao, H., & Zhang, F. (2025). Investigating bidirectional causal relationships between gut microbiota and insomnia. General Psychiatry, 38, e101855. https://doi.org/10.1136/gpsych-2024-101855