A massive study of nearly 400,000 people has for the first time established a causal link between gut bacteria and insomnia, confirming previous observational research that found some bugs help you sleep while others disrupt it. Fourteen bacterial taxa were found to increase the risk of insomnia, while eight appeared to be protective.
Research led by a team at The Affiliated Brain Hospital of Nanjing Medical University in China investigated the relationship between insomnia and gut bacteria. The researchers wanted to see whether certain microbes made it harder to sleep, and if insomnia, in turn, changed which microbes live in your gut – and if this then fed back into sleep disorders.
In a large-scale analysis, the researchers drew on genome-wide association study (GWAS) data from 386,533 participants in the UK Biobank, which featured 109,402 with insomnia and 277,131 without. They then paired it with gut flora data from two major microbiome projects – the MiBioGen alliance, which included 18,340 participants with detailed genetic and gut bacteria profiles, and the Dutch Microbiome Project, with 8,208 individuals.
But instead of finding associations, the team used Mendelian randomization (MR) to tease out any cause-and-effect evidence in the datasets. MR uses our genes as a type of "nature study" to work out whether one thing is likely to cause another. And because genetic variants aren’t changed by environment or disease, they can help sort data like a randomized clinical trial. If a gene variant that makes someone more likely to have a certain gut bacterium is also linked to a higher risk of insomnia, and other explanations are ruled out, that’s strong evidence the bug may play a role in causing sleep issues. This approach helps untangle cause from coincidence – and rules out confounding factors better than with observational studies.
What they uncovered was a complex picture of how our gut and sleep interact. Fourteen bacterial taxa were found to increase insomnia risk, while eight looked to shield us from poor sleep. The strongest signal came from the Clostridium innocuum group, where a higher genetic predisposition to abundance was matched with a greater likelihood of suffering from insomnia. Others (from the MiBioGen cohort) that looked to be factors contributing to poor sleep included Prevotella 7, Lachnoclostridium, ParaPrevotella, Family XIII AD3011 group, Rikenellaceae RC9 gut group and Parabacteroides, class Negativicutes and order Selenomonadales.
In the Dutch cohort, "The genera Pseudoflavonifractor and Anaerotruncus, species Veillonella unclassified, Bacteroides massiliensis and B. faecis are associated with increased risks of insomnia," the researchers noted in their results.
While that's a lot to swallow, so to speak, perhaps the ones to swing the good-sleep odds back in your favor are the bacteria to focus on. Combining both genome cohorts, the researchers identified: The genera Coprococcus1 and Lactococcus, family Actinomycetaceae and order Actinomycetales, genus Odoribacter, family Clostridiaceae and species Ruminococcus torques and R. lactaris contributed to reducing insomnia risk.
Then, after adjusting for the possibility of false positives, the only statistically strong finding that remained was that having more of the Clostridium innocuum group delivered a higher risk of insomnia.
However, another interesting piece of data emerged – one genus had a two-way relationship with insomnia, influencing poor sleep and, in turn, that poor sleep creating the environment for these types of bugs to flourish in numbers.
"We also discovered bidirectional causal relationships between the genus Odoribacter sourced from the Dutch Microbiome Project and insomnia," the team wrote. "Following the execution of the Steiger test, these positive causal relationships were confirmed as being significant."
While you don't necessarily need to know all of these groups or species living in your gut, the research highlights how this connection once again shows that behaviors are influenced by the gut-brain axis – the network of chemical, neural and immune signaling between the digestive tract and the central nervous system. This is something that scientists are increasingly focusing on to identify markers of disease and mental health conditions – and to find new treatments that don't instead destroy the microbiome's diversity.
Some bacteria, including several identified as protective in this study, produce short-chain fatty acids such as acetate, propionate, and butyrate, which can influence brain signaling and inflammation. Others can metabolize tryptophan into serotonin, the neurotransmitter that is then converted into melatonin, the hormone that regulates our sleep–wake cycle.
Meanwhile, poor sleep can trigger stress and inflammatory responses in the body, altering the gut environment in ways that boost the populations of some species of microbes over others. This can create a feedback loop, with insomnia and microbiota "feeding" into each other.
It should also be noted there are limitations to the study, All participants were of European ancestry and the genetic MR approach ignores other insomnia influences such as diet, lifestyle and geography. In addition to this, switching up the abundance of one potentially helpful microbe is not fully understood, since the microbiome works as a complex, interconnected ecosystem.
And while eating one type of food doesn't "deposit" microbes into the gut, it creates the environment that encourages their growth. For example, Coprococcus 1 species – which help with serotonin release – are best supported by high-fiber plant foods like whole grains, leafy green vegetables and legumes, as well as polyphenol-rich berries and tea. Odoribacter species are encouraged by consuming whole grains, legumes, nuts, a variety of vegetables and some animal-based proteins (in moderation). And Lactococcus species are "transient" – they are less likely to stick around in the gut – so a regular intake of fermented foods (yogurt, kefir, sauerkraut, kimchi, tempeh) is the best way to maintain their populations.
While it's still early days, this study advances our understanding of the biological link between microbes and our minds, suggesting that treating insomnia should be more of a whole-body approach, rather than focusing just on the brain.
And it opens the door to microbiome sampling for identifying insomnia triggers, as well as treatments that target the gut – including probiotics, prebiotics, dietary changes or microbial transplants – to help treat sleeping disorders.
The study was published in the journal General Psychiatry.
Source: Nanjing Medical University via MedicalXpress
