There is an increasing prevalence of insomnia. A cross-sectional study measured that insomnia and sleep difficulties had increased from 17.5% to 19.2% among adults in the United States. Another cross-sectional study, with data from a 2011-2012 health survey among 54,722 European adults, also reported high prevalence rates for sleep problems, ranging from 16.6% to 31.2%. These numbers can have detrimental consequences for public health, as insufficient sleep is associated with an increased risk of cardiometabolic diseases, respiratory diseases, and tumour formation. Sleeplessness has furthermore been found to negatively affect cognitive function, increase stress, and decrease motivation. Therefore, an effective method to improve sleep quality is urgently needed. Therefore, an effective method to improve sleep quality is urgently needed.
Several studies indicated that a lower sleep quantity and quality are associated with a dysbiotic gut microbiome, i.e. an altered composition and function of the gut microbiome that can be characterised by a lower microbial diversity, the increase of pathogenic microbiota, or the loss of beneficial microbes. Microbial metabolism produces a variety of neurotransmitters, cytokines, and metabolites such as 5-HT, dopamine (DA), GABA, short-chain fatty acids (SCFAs), melatonin, and other compounds. Those metabolites not only act directly on the enteric nervous system (ENS) and the vagus nerve but also affect the activity of the central nervous system (CNS) by regulating enteroendocrine cells in autocrine or paracrine fashion.
A study in which mice received a diet containing the heat-killed Levilactobacillus brevis tended to spend an increased time in NREM (Non-Rapid Eye Movement) and REM (Rapid Eye Movement) sleep during their inactive phase compared with control mice that received a normal chow diet. The mice also spent significantly more time in wakefulness during the second half of their active phase as compared with the control mice. In vitro studies demonstrated that a wide variety of microbial strains can produce neurotransmitters and their precursors, which are involved in sleep regulation. Researchers suggested that the neurotransmitters might act via the gastrointestinal neurons of the vagus nerve, the afferent gastrointestinal neurons signal to the central terminals of the vagus nerve and, in turn, pass the signal to the brain and influence sleep regulation via the vagus nerve. In a similar vein, there is some limited evidence in humans of a decrease in biomarkers of stress upon probiotic administration, and reduced levels of stress can improve sleep quality. Nishida et al., using Lactobacillus gasseri CP2305 intervention in tablet form, reported an improvement in perceived sleep quality and less awake time after sleep onset, more depth of sleep, and a shortened time to reach the deep stage of sleep.
While some studies have found improvements in sleep latency and sleep length after probiotic treatment, other studies have not shown any significant improvements in sleep quality, stress, or anxiety. Therefore, more prospective studies are needed to investigate the potential of probiotics to improve sleep quality and address sleep problems that are increasingly common worldwide.
  1. J.E. Haarhuis, A. Kardinaal and G.A.M. Kortman: Probiotics, prebiotics and postbiotics for better sleep quality: a narrative review. Beneficial Microbes, 2022; 13(03): 169-182
  2. Anna Chu , Samir Samman, Barbara Galland and Meika Foster.: Daily consumption of Lactobacillus gasseri CP2305 improves quality of sleep in adults e A systematic literature review and meta-analysis. Clinical Nutrition 42 (2023) 1314-1321