When we fall asleep, the work in the body does not stop. Trillions of "neighbors" work together with our cells - microorganisms in the intestine and oral cavity. In recent years, science has consistently shown that the composition of these microbial communities is associated with the quality of sleep. It's not just about general well-being - the diversity of the microbiome, the level of inflammation and metabolic signals inside us depend on the duration and structure of night's rest.
At first, scientists suspected that everything worked in one direction: lack of sleep and sleep disorders upset the microbiome. Now the data also suggests the opposite effect. In adolescents and young adults, a more diverse oral microbiome is associated with longer sleep. People with medically diagnosed insomnia are more likely to have a poorer composition of gut bacteria compared to those who sleep normally. Even in small observations with sleep trackers for a month, poorer quality of rest correlated with less diversity of gut microflora. And in groups with “social jet lag” — sharp shifts in regime between weekdays and weekends — the microbial profile was noticeably different from the profile of people with a stable schedule.
The mechanism of this connection is quite material. Bacteria produce short-chain fatty acids (for example, butyrate), modulate the immune response and synthesize a number of neurotransmitters - from serotonin and dopamine to gamma-aminobutyric acid. All these are links of the "gut-brain" axis, which affect circadian rhythms, the depth of slow sleep and the phase of rapid eye movement. When the balance of microbes shifts towards an inflammatory profile (excess sugar and saturated fats in the diet, chronic stress, antibiotics), the level of pro-inflammatory molecules and bile acids increases, which can upset the brain's "clock" and worsen sleep.
Similar processes occur in the oral cavity. Poor hygiene or nutrition alters the oral microbiome, increases local and systemic inflammation, and can lead to narrowing of the airways during sleep. Against this background, the risks of snoring and obstructive sleep apnea, a condition in which breathing is interrupted and the body is chronically deprived of oxygen, increase.
Is there causality here, not just associations? There are early clues. In model experiments, transplanting gut microbes from people with disrupted sleep patterns and insomnia caused behavioral signs of sleep disorders in mice. Small pilot trials in humans suggest that microbiome correction may improve symptoms of chronic insomnia. Even brief interventions—like a week of a high-fat, high-sugar diet—have markedly altered the brain’s electrical patterns during deep sleep in healthy volunteers; and antibiotics have reduced REM sleep duration in some trials. This is not evidence for clinical standards, but it points the way.
Does this mean that the “bacteria pill” will become the new sleeping pill? It’s too early to draw such conclusions. Certain strains—such as Lactobacillus casei Shirota—have been shown to improve sleep in young people under controlled conditions during periods of stress, but these results need to be confirmed in large randomized trials and compared with established approaches like cognitive behavioral therapy for insomnia. At the same time, the idea seems appealing: if we restore the balance of the microbiome with nutrition, prebiotics, or carefully selected probiotics, we may be able to reduce the proportion of people with chronic sleep disorders—from the effects of changing lifestyles to age-related problems.
The practical conclusion for today is simple and safe: a stable bedtime schedule, sufficient fiber in the diet, moderate consumption of sugar and saturated fats, sensible oral hygiene and limiting late-night snacks support not only the heart and metabolism, but also the microbiome that “underlies” our sleep. However, experiments with supplements and aggressive interventions are best left under the supervision of a doctor - the evidence base for “bacterial” methods is still forming, and much work lies ahead before they become routine, just like today's hygienic sleep rules.
