There seem to be reciprocal links between certain groups of gut bacteria and the risk of insomnia, suggests a Mendelian randomisation study, published in the open access journal General Psychiatry.
Certain types of bacteria seem to boost or lower the risk of the sleep disorder while insomnia itself seems to alter the abundance of certain types of bacteria, the findings indicate.
Several studies have explored the effects of the gut microbiome on various sleep characteristics, but it's not yet clear how different groups of gut bacteria might affect the risk of insomnia, which affects an estimated 1 in 10 to 1 in 5 people, say the researchers.
To strengthen the evidence base, they deployed Mendelian randomisation analysis, a technique that uses randomly selected genetic variants as proxies for a particular risk factor to obtain genetic evidence in support of a particular outcome.
They drew on data for 386,533 people with insomnia from a previously published genome wide analysis study and gut microbiome data for 18,340 people from the MiBioGen alliance , and for 8208 people from the Dutch Microbiome Project (71 groups of bacteria in common).
The analysis revealed associations between specific gut microbes and insomnia. In all, a total of 14 groups of bacteria were positively associated (1-4% higher odds), and 8 groups negatively associated (1-3% lower odds), with insomnia.
And insomnia was itself associated with a reduction of between 43% and 79% in the abundance of 7 groups of bacteria, and a 65% to a more than fourfold increase in the abundance of 12. The Odoribacter class of bacteria, in particular, was significantly associated with the risk of insomnia.
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, note the researchers.
The findings agree with those of many previously published studies that have suggested an interplay between insomnia and the gut microbiome, but certain limitations should be borne in mind, caution the researchers.
All the study participants were of European descent, so the results may not be more widely applicable as the make-up of the microbiome varies among different ethnicities and geographies, they point out. And factors, such as diet and lifestyle, all of which affect the microbiome and the interplay between genes and the environment, weren't accounted for.
"Overall, the intertwined effects of insomnia on gut microbiota, and vice versa, represent a complex bidirectional relationship involving immune regulation, inflammatory response, release of neurotransmitters, and other molecular and cellular pathways," they explain.
And they conclude: "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."
These might include the use of probiotics, prebiotics, or faecal microbiota transplantation, they suggest.
