Serotonin is a key neurotransmitter responsible for our happiness . 95% of the bodies total serotonin levels are located in the gastrointestinal tract and accumulating evidence points out the importance of the microbiome in the serotonin production . Tryptophan is an essential amino acid and the precursor for serotonin production. Tryptophan is used for serotonin production in the enterochromaffin cells of the gastrointestinal tract (GI). Unlike mammalian cells (or all eukaryotes), bacteria can synthesis tryptophan and there are even a few specific bacterial strains that produce serotonin, including some Lactobacilli species, Streptococcus thermophilus and Bifidobacterium infantis.
Interestingly, germ-free mice exhibit elevated hippocampal serotonin concentrations while germ-free rats showed a decrease . Showing that the microbiome is important for this process, even though we do not yet completely understand how and in which direction.
To support the notion that certain bacteria species can help to elevate serotonin levels, researchers used probiotics, containing Bifidobacteria infantis to rise serotonin levels in rats . They found that the blood concentration of tryptophan, the precursor of serotonin, was nearly two times as high in rats fed with the probiotic compared to the control.
One of the most prescribed drugs for depression are selective serotonin reuptake inhibitors which are believed to increase serotonin levels. However, these studies give us an indication that our microbiome plays a role in serotonin production and that perhaps a disrupted microbiome can be one reason for people to develop depression. At the very least, somebody with strong mood changes or depression should give it a try to improve his/her gut health.
- Berger et al., The expanded Biology of Serotonin, Annu Rev Med, 2009
- O'Manhony et al., Serotonin, tryptophan metabolism and the brain-gut-microbiome axis, Behavioural Brain Research, 2014
- Clarke et al., The microbiome-gut-brain axis during early life regulates the hippocampal serotonergic system in a sex-dependent manner, Molecular Psychiatry, 2013
- Desbonnet et al., EFFECTS OF THE PROBIOTIC BIFIDOBACTERIUM INFANTIS IN THE MATERNAL SEPARATION MODEL OF DEPRESSION, Neuroscience 2010