Snug with your bugs? How microbes control your sleep

But there are other reasons to think it might work. Diet, for example, is well known to affect sleep. When a group of 15 healthy young men followed a high fat, high sugar diet for a week, this altered their brains’ electrical patterns during deep sleep, although it’s hard to draw firm conclusions from such a small sample size. Similarly, in an experiment where volunteers had their sleep assessed after receiving antibiotics, evidence suggested that this reduced the amount of non-rapid eye movement sleep, an essential part of the sleep cycle where our bodies undergo repairs and new memories and skills are reinforced, although the findings did not apply for all antibiotics, and once again, the study was small.

Changes in the balance of our gut microbes may also alter the amounts of useful chemicals they produce as they help to break down our food. This in turn can influence sleep quality, says Tartar.

We know, for example that some gut microbes produce neurotransmitters such as gamma-aminobutyric, dopamine, norepinephrine and serotonin, or short-chain fatty acids such as butyrate, all of which play a role in sleep. “While they’re produced in the gut, they can influence [the] brain,” says Tartar.

If those microbes decrease in abundance, then their chemical influence on the brain will likely also lessen while other microbes that use foods such as saturated fat and sugar to synthesise inflammatory molecules can proliferate. Some of these inflammatory chemicals, including certain bile acids, are thought to be capable of disrupting the brain’s circadian rhythms. 

Martin says the same is likely to be true of the oral microbiome. Heightened inflammation, caused by microbes flourishing in people who have poor diets or poor dental health, could raise those individuals’ risk of issues including obstructive sleep apnoea, in which the walls of the throat relax during sleep, interrupting normal breathing.