Serotonin & Your Microbiome

You may have heard that your gut makes about 95% of your body’s total serotonin, but this “peripheral” serotonin actually can’t get into the brain (in other words, it can’t cross what we call the “blood-brain barrier”).

So then, how does your gut microbiome impact your serotonin levels?

If you haven’t been introduced to serotonin before, it’s a substance in your body (known as a “neurotransmitter”) that is responsible for your general sense of well-being and happiness. It is  the main neurotransmitter affected by anti-depressant drugs like Prozac and Zoloft, which improve mood by boosting serotonin action in your brain. Serotonin is made in your body by the enterochrommafin cells in your gut, and in your brain in the raphe nuclei.

It appears that some of the not-so-helpful bacteria in your gut stimulate the production of pro-inflammatory “cytokines.” Cytokines are cell signalling proteins that allow our cells to communicate with each other, and are important in inflammation, immune function, and disease modification. And in this case, pro-inflammatory cytokines tell our bodies to divert tryptophan (the precursor to serotonin) from our brains. Ideally, if we have a healthy amount of circulating tryptophan (which can cross the blood-brain barrier, whereas serotonin can’t), there is plenty of it available in our brains to make a heap of serotonin… which again, contributes to our generally happiness and contentment.

So, in short: dysbiosis (too many bad bacteria) = increased inflammatory cytokines = less tryptophan available = lowered serotonin production.

And though we don’t know for sure, lowered serotonin levels in the brain appear to be related to changes in mood, cognitive function, and behavior. Seems like another way that the gut, our microbiome, and brain are directly related… and further evidence that when your gut microbiome is balanced and happy, you are balanced and happy.

Pass the sauerkraut, please!