What does too little sleep do to your gut?

Sleep deprivation disrupts the composition of your gut bacteria. Both short sleep duration and fragmented sleep have been linked to dysbiosis: an imbalance in the gut flora in which unfavourable bacterial species gain the upper hand. One possible explanation is that sleep deprivation activates the body's stress hormone system, which alters the gut environment.

A concrete casualty of that disruption is butyrate, a substance produced by healthy gut bacteria. In people with insomnia, lower butyrate levels in the blood have been found, alongside fewer butyrate-producing bacteria. Noteworthy is what happened in mice: when the gut flora of insomnia patients was transferred to a mouse, the animal developed sleep disturbances. When those mice were subsequently given butyrate orally, the disturbances disappeared. Whether this translates directly to humans is not yet known.

There is also a vicious cycle: sleep deprivation alters the gut flora, and that altered flora in turn makes you more fatigued. Certain bacterial species that thrive under conditions of sleep deprivation appear to amplify fatigue in the host. Exactly how remains not yet fully understood.

In the long term, gut changes caused by sleep deprivation can contribute to metabolic problems. Sleep deprivation and a high-fat diet both dampen the normal daily fluctuations in bacterial composition, which increases the risk of overweight and diabetes. In children with sleep apnoea, an altered gut microbiome has also been found, which may contribute to high blood pressure and overweight through immune and metabolic pathways.

Probiotics are being investigated as a possible way to improve sleep quality, but the evidence for this is thin and the mechanisms of action remain unclear. What is concrete: sleeping well protects your gut flora, and a healthy gut flora in turn appears to support sleep via butyrate. That interplay is the most well-supported finding from this field of research.