We're learning more and more about how parts of our bodies are linked and working together – and now a new study reveals connections between gut bacteria and the risk of insomnia.
The research, from scientists in China and the US, suggests that being unable to sleep at night could be at least partly down to the mix of microbes in our digestive system.
What's more, the relationship appears to go both ways: poor sleep can disrupt the gut's microbial balance, creating a feedback loop that could make insomnia harder to shake. With further investigation, we may be able to develop treatments based on these findings.
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"Changes in the composition and function of the gut microbiota are commonly noted in patients with insomnia," write the researchers in their published paper.
"However, their causal connections to insomnia phenotypes are far from being clear."
The team, led by psychiatrist Shangyun Shi of Nanjing Medical University, used a statistical approach called Mendelian randomization. This method looks at genetic variations – which are set at birth and unaffected by lifestyle and other factors – to help determine whether one factor is truly influencing another.
By analyzing genetic and health data from more than 400,000 people, the researchers found several clear matches. Certain types of bacteria were associated with increased insomnia risk, while others seemed to lower the odds.
The strongest evidence pointed to the Clostridium innocuum group of bacteria being linked to a greater risk of insomnia. It's not normally a dangerous kind of bacteria, but it appears to be contributing to sleepless nights for some.
"We identified a total of 14 and 8 bacterial taxa, respectively, as positively and negatively correlated with insomnia," write the researchers. "In addition, there were reverse effects of insomnia correlated with 19 identified microbial taxa."
Scientists already know the gut-brain axis works in two directions, and previous research has linked it to stress levels, neurodegenerative diseases, and conditions such as autism and ADHD.
The researchers behind this study think that some of the chemical reactions that certain bacteria start or stop might explain the new findings. We're still at the early stages here, and further studies are going to be required in diverse populations – all the participants in this study were of European descent.
It's worth noting that gut microbes are only one piece of the insomnia puzzle. Other factors can contribute, from stress at work to drinking habits. But it appears that gut bacteria are definitely a factor to look at in more detail.
Eventually, prebiotics and probiotics could be developed to take advantage of this link, and poop transplants might also work as a way of treating insomnia – something that's being looked at for multiple conditions.
"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," write the researchers.
The research has been published in General Psychiatry.