A Little Serotonin Can Go A Long Way

Today’s blog is one of my favorite topics to discuss. It’s our “happy hormone,” but to be honest, serotonin is so much more than just happiness. It plays a role in how we think, how we feel, how we sleep, and how we respond to stress on a day-to-day basis. What makes serotonin even more interesting is where it is made. Serotonin is produced both in the gut and in the brain, but these two pools function very differently. The gut is lined with cells that produce serotonin, however this serotonin cannot cross the blood–brain barrier. What is made in the gut stays in the gut, and what is made in the brain stays in the brain.

In the gut, serotonin plays a key role in motility. It helps regulate how food moves through the digestive system, and disruptions here can often show up as constipation or changes in bowel habits. In the brain, serotonin production is dependent on a number of co-factors, including iron, zinc, vitamin D, and folate. This is where things become more nuanced. Genetic SNPs can influence how well you utilize these nutrients, and the gut microbiome can either support or impair their absorption. So even when the diet looks “good,” the internal environment may not always allow for optimal serotonin production.

When we talk about serotonin, we also have to talk about its receptors. These receptors determine how effectively serotonin can do its job. You could have adequate levels of serotonin, but if receptor sensitivity or function is altered, the outcome in the body can look very different. This is where the conversation becomes more nuanced. It is not simply about increasing serotonin, but about understanding how the system as a whole is functioning. This includes genetics, receptor expression, and the balance with other neurotransmitters.

One of the most important relationships here is between serotonin and GABA. GABA is the brain’s primary inhibitory neurotransmitter, the one that allows us to slow down, feel calm, and regulate anxiety. Receptors such as GABRA play a role in how effectively this calming signal is received. In individuals who are chronically stressed, this balance can shift. The body starts to favor cortisol production over calming pathways, and over time this can create a picture of anxiety, poor sleep, and emotional reactivity. What may have worked well in your 30s may no longer feel as effective, not because something is “wrong,” but because the system is under a different level of demand.

This is also where the gut microbiome becomes central to the conversation. It doesn’t just influence digestion, it influences neurotransmitter activity and receptor sensitivity. Certain probiotics, such as Lactobacillus plantarum, have been shown to influence serotonin receptors in the gut, which can then have downstream effects on the hypothalamic–pituitary axis, the HPA axis, and ultimately our stress response. The fermentation of dietary fibers by gut bacteria produces metabolites such as short-chain fatty acids, including butyrate, which help maintain gut integrity, reduce inflammation, and support communication along the gut–brain axis . When this system is compromised, it can influence not only digestion but also mood, cognition, and emotional stability.

Mental health is something I look at closely with all of my clients, not just because it is a passion of mine, but because of the times we are living in. Chronic stress has become the norm, and it directly impacts gut health and hormonal balance. We are seeing more dysbiosis, more nutrient deficiencies, and more individuals struggling with anxiety and low mood. Hormone replacement therapy has its place, but it isn’t always the full answer. Increasingly, we are looking at the gut microbiome as a central control system, influencing everything from neurotransmitter production to hormone metabolism. Instead of simply giving precursors like tryptophan or tyrosine, my goal is always to improve the gut’s ability to absorb and utilize these nutrients effectively.

In our modern world, we have a whole host of tools available to us. Probiotics, prebiotics, ketogenic diets, exercise, and mindfulness can all play a role. The challenge is not the lack of options, but the confusion around what to actually do. My approach has always been to use everything we have, but to do so with intention. Science has come a long way, but it doesn’t always translate quickly into everyday practice. When you start to look at serotonin through this lens, happiness is no longer just a chemical imbalance. It becomes a reflection of how well the entire system is functioning. And sometimes, a little serotonin, supported in the right way, can go a very long way.