A new study has found compelling evidence that certain gut bacteria may influence the risk of insomnia — and that insomnia itself can alter the composition of the gut microbiome. The research, published in the open-access journal General Psychiatry, suggests a complex, bidirectional relationship between the two.
Using Mendelian randomization — a genetic analysis method that uses randomly assigned genetic variants to explore cause-and-effect relationships — researchers examined genetic and microbiome data from multiple large datasets.
These included 386,533 individuals with insomnia from a previous genome-wide association study, microbiome data for 18,340 people from the MiBioGen alliance, and 8,208 participants from the Dutch Microbiome Project, covering 71 bacterial groups in common.
The findings identified 14 bacterial groups associated with a 1–4% increased risk of insomnia and eight groups linked to a 1–3% reduced risk. Conversely, insomnia was linked to substantial shifts in gut microbiota: reductions of 43–79% in seven bacterial groups and increases ranging from 65% to more than fourfold in 12 groups. Notably, the Odoribacter genus showed a particularly strong connection to insomnia risk.
No evidence of genetic pleiotropy — where a single gene influences multiple unrelated traits — was detected, strengthening the case for a causal relationship.
While the study reinforces earlier findings on the gut–sleep connection, researchers note important limitations. All participants were of European ancestry, making the results less generalizable to other populations with different microbiome compositions. In addition, the analysis did not account for lifestyle factors such as diet, which can significantly influence gut bacteria.
The researchers propose that the interplay between insomnia and gut bacteria may involve immune regulation, inflammatory pathways, neurotransmitter release, and other biological mechanisms. They suggest the findings could eventually lead to new microbiome-based insomnia treatments, including probiotics, prebiotics, or even fecal microbiota transplantation.
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