Bad night’s sleep? It’s not uncommon to crave the comfort of a full-fat, sugar-encrusted doughnut. Equally, a large dinner of fried food might leave you tossing and turning in bed and waking drained the next day. But food isn’t necessarily the common denominator here. Increasingly, evidence suggests that the gut microbiome – the bacteria and other micro-organisms in our digestive tract – can influence the quality of our sleep.
Research into the microbiome and its role in health and behaviour has been a hot topic for several years, with research suggesting links between gut bacteria and various diseases and mental health disorders, including cancer and depression. Now scientists believe that there seems to be a relationship with sleep too.
Dr David Gozal, professor of child health, medical physiology and pharmacology at the University of Missouri School of Medicine, is one of those scientists.
“Sleep is very likely to influence the gut microbiome,” he says. “Conversely, it is very likely that changes in the microbiome will influence sleep.”
Gozal has put this theory to the test in mice. His team transplanted faecal material from mice that had been genetically engineered to have the chronic condition obstructive sleep apnoea (OSA) into a group of normal mice. The study, published in the journal Experimental Neurology, found that the normal mice developed the OSA symptom of increased sleepiness. According to Gozal, the transplant altered the gut microbiome of the normal mice and affected their sleep.
Meanwhile, several studies have shown that people who sleep better have a more diverse and healthy gut microbiome – and they tend to be in better health generally. This is a big deal when the US Centers for Disease Control and Prevention deem insufficient sleep to be a public health problem.
“Disrupted sleep may be as bad as an unhealthy diet for the health of the gut microbiome,” says Dr Emeran Mayer, research professor of medicine at the University of California, Los Angeles, and author of The Gut-Immune Connection.
How the gut microbiome talks to the brain
The interaction between the digestive system and sleep comes down to what’s known as the brain-gut microbiome axis, which enables a bidirectional flow of information between the two systems. This is likely to be influenced by the microbiome’s own circadian rhythm and the regulation of sleep genes, according to Mayer.
It’s also believed that gut bacteria produce basic molecules from food called metabolites, which are shuttled to, or communicate with, the brain through the axis. While the research is in its infancy, there are numerous theories as to how this might happen. One is that the microbiome could affect the immune system and vary the level of immune-signalling molecules such as cytokines. Another is that it could regulate chemical messenger molecules called neurotransmitters, including the stress hormone cortisol.
A recent study in Japan, published in Scientific Reports, highlights the role that metabolites might play. Researchers compared the intestinal contents of normal mice with those that had a depleted gut microbiome. All mice were fed the same diet, but the researchers found that the metabolites were different in the two groups. Significantly, the mice with depleted microbiomes didn’t appear to have the bacteria that convert the amino-acid tryptophan in food into the sleep hormone serotonin. These mice had disrupted sleep patterns.
Could improved gut health be a new sleep therapy?
This all leads to a tantalising proposition: if we altered our diet or the microbiome of our gut, could we improve our sleep? The idea certainly holds some promise. Take prebiotics – fibre compounds in food that feed the beneficial gut bacteria. Another study published in Scientific Reports found that rats on a prebiotic diet not only slept better than those on a non-prebiotic diet; they were also better at dealing with stress. Digging deeper, the researchers found the rats on the prebiotic diet had fewer sleep-disrupting metabolites.
They are cautiously optimistic that their findings could lead to new approaches in the treatment of sleep problems. One of the co-authors of the research is Dr Monika Fleshner, professor of integrative physiology at the University of Colorado. She says that the discovery of “an innovative alternative to sleep medications is desirable. The next step is to figure out which specific dietary prebiotics can affect which types of gut bacteria.”
Dr Jaime Tartar, neuroscience programme director at Nova Southeastern University in Florida, warns that the relationship between the gut microbiome and sleep is a complex one. “I don’t think the answer for significantly better sleep will be simply to supplement the diet with one particular prebiotic,” she says. “But this research area holds the promise of directing us towards how we can improve sleep through diet.”
Are ‘sleepbiotics’ the future?
Manipulating the gut microbiome could target numerous health problems associated with poor sleep, such as cardiovascular disease and diabetes. Gozal believes that a greater understanding of the microbiome in health heralds a new approach to sleep.
“This opens unique opportunities for ‘sleepbiotics’ and the development of approaches to promote healthy sleep, as well as the treatment of sleep disorders using personalised interventions,” he says.
Indeed, Unilever has recently joined forces with Microba Life Sciences to explore this very area.
“People need to treat sleep not as an expendable commodity but rather as a major long-term determinant of health and wellness,” Gozal adds. The gut microbiome has a role to play in this, but we are only just starting to discover its nature and extent.