Some Gut Bacteria Cause Insomnia While Others Protect Against It, 400,000-Person Study Argues

For the first time, researchers have managed to establish what looks like a causal and reciprocal relationship between the bacteria in our guts and insomnia. The work indicates that certain bacteria can increase the risk of suffering this sleep disorder, while others can help prevent it. However, the results show that insomnia itself can alter the abundance of some types of bacteria as well.

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Insomnia is an extremely common sleep condition that is characterized by difficulty falling asleep or subsequent poor sleep quality. This can be accompanied by fatigue and irritability, which can negatively affect daily life. It is estimated that around 10 to 20 percent of the population suffers from insomnia. It’s a bit of a slippery slope condition: insomnia can lead to the development of other medical and mental disorders that contribute to ill health or even increased mortality, as well as societal costs.

The causes of insomnia are complex, involving the interaction of genetics with environmental factors, behavior, and physiological factors that come together to produce too much wakefulness. But it is also known that insomnia patients often experience changes in their gut microbiota, though a causal connection has not yet been established.

That’s what this latest study sought to address. Past research has shown that gut bacteria can have impacts on sleep characteristics, but it is not clear how different groups of bacteria might affect the risk of insomnia. In order to strengthen the evidence for this idea, the team used a technique known as Mendelian randomization analysis. This essentially uses naturally occurring genetic differences – which are inherited from parents – as a way to see whether a specific risk factor (such as gut bacteria) can cause a specific outcome (like insomnia), instead of them just being associated with one another.

The team assessed data from 386,533 people with insomnia, which they collected from a previously published genome-wide analysis study. This was coupled with gut microbiome data for 18,340 people taken from the MiBioGen alliance, and for 8,208 people from the Dutch Microbiome Project.

The results found that a total of 14 groups of bacteria were positively associated with insomnia (1 to 4 percent higher odds), while eight group were negatively associated with it (1 to 3 percent lower odds).

On the flip side, insomnia was found to be associated with reducing between 43 and 79 percent of the abundance of seven groups of bacteria. At the same time, it led to a 65 percent to more than 300 percent increase in the abundance of 12 groups. In particular, the Odoribacter genus of bacteria – an important type of gut bacteria – were found to be associated with the risk of insomnia.

The researchers also explain that they found no evidence of pleiotropy – the production by a single gene of two or more supposedly unrelated effects. This, they believe, strengthens the argument that this is a causal relationship. These findings build on many previously published studies, but some limitations still remain.

For one thing, all the participants were of European descent, so the results may not be generalizable, as gut biomes vary between ethnicities and geographies. At the same time, things like diet and lifestyle can also significantly impact the microbiome and the relationship between genes and the environment. None of these factors were accounted for in the present results.

"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," the researchers explain.

"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 study is published in General Psychiatry.