Recent evidence suggests that the status of our gastrointestinal flora may affect mood and behavior. This evidence, derived from a study conducted by Bravo et al. and published in the Proceedings of the National Academy of Sciences, suggests that bacteria in the gut can communicate with the brain via the vagus nerve1. (The vagus nerve transmits signals between the gastrointestinal system and the brain.).
The study examined 2 groups of mice who were fed either a diet containing Lactobacillus rhamnosus (a beneficial bacteria found in dairy products and many probiotic supplements) or a diet without this bacteria. Emotional and mood states of each group of mice were evaluated and it was found that the mice fed the diet with L. rhamnosus generally responded to tests in such a way that suggested improved mood and decreased anxiety than the group of mice fed a diet without probiotics. In addition, the L. rhamnosus-fed mice exhibited lower levels of corticosterone than the mice fed a diet without probiotic organisms. (Corticosterone is a hormone secreted in response to stress.) Furthermore, all of these differences disappeared when the vagus nerves of the mice in both groups were cut, suggesting that the effects were mediated by gut-brain communication.
While the above study was conducted on animals and the results are not directly translatable to humans, evidence from other studies suggest reason to pursue this research further:
- There is evidence that probiotics (and prebiotics) can improve mood and decrease anxiety in patients with irritable bowel syndrome and chronic fatigue syndrome.2,3
- Epidemiological evidence has identified an association between neurodevelopmental disorders (such as schizophrenia) and microbial pathogen infections during the perinatal period.4
- Colonization of the gut with beneficial microbes can impact brain development and subsequent adult behavior (according to another recently published study in the Proceedings of the National Academy of Sciences5).
Thus it seems all the more important to consider not only treating the brain and nervous system in those suffering from mental-emotional distress, but also to focus on gastrointestinal health. No wonder so many herbs and natural remedies that are of benefit to the nervous system are also of benefit to the gastrointestinal system—the health of each system may be more interdependent than modern medicine has heretofore appreciated.
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1Bravo JA, Forsythe P, Chew MV, et al. (2011) Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proc Natl Acad Sci USA 108:16050-55.
2Rao AV, Bested AC, Beaulne TM, et al. (2009) A randomized, double-blind, placebo-controlled pilot study of a probiotic in emotional symptoms of chronic fatigue syndrome. Gut Pathog 1:6.
3Silk DB, Davis A, Vulevic J, et al. (2009) Clinical trial: The effects of a trans-galactooligosaccharide prebiotic on faecal microbiota and symptoms in irritable bowel syndrome. Aliment Pharmacol Ther 29:508-18.
4Mittal VA, Ellman LM, Cannon TD (2008) Gene-environment interaction and covariation in schizophrenia: The role of obstetric complications. Schizophr Bull 34:1083-1094.
5Heijitz RD, Wang S, Anuar F, et al. (2011) Normal gut microbiota modulates brain development and behavior. Proc Natl Acad Sci USA 108:3047-3052.
The Economist, 400(8749), 80-81.