- Serotonin is a vital neurotransmitter and hormone that plays a central role in regulating a wide range of physiological and psychological processes.
- Chemically known as 5-hydroxytryptamine (5-HT), serotonin is synthesized from the essential amino acid tryptophan, which is obtained through the diet. It is found throughout the body but is most concentrated in three primary areas: the central nervous system (CNS), the gastrointestinal (GI) tract, and blood platelets. Despite its widespread presence, serotonin is perhaps best known for its influence on mood, emotion, and behavior.
- In the brain, serotonin acts as a neurotransmitter that facilitates communication between neurons. It is involved in regulating mood, anxiety, sleep, appetite, memory, and learning. Adequate serotonin levels are associated with a stable mood and a sense of well-being, while deficiencies or imbalances have been strongly linked to depression, anxiety disorders, obsessive-compulsive disorder (OCD), and other mood-related conditions. Many antidepressant medications, particularly selective serotonin reuptake inhibitors (SSRIs) like fluoxetine and sertraline, work by increasing serotonin availability in the brain, thereby enhancing its mood-regulating effects.
- Outside the CNS, about 90–95% of the body’s total serotonin is found in the gastrointestinal tract, where it plays a key role in regulating intestinal movements, digestion, and gut motility. It is secreted by enterochromaffin cells in response to food intake and stimulates muscle contractions in the intestines. Serotonin in the GI system also helps mediate nausea, appetite, and bowel function. This strong presence in the gut explains the close connection between mental health and gastrointestinal health, often referred to as the “gut-brain axis.”
- Serotonin also circulates in the bloodstream, stored in platelets, where it contributes to blood clotting by helping platelets aggregate at the site of a wound. It also influences vascular tone by affecting the contraction and relaxation of blood vessels. Additionally, serotonin impacts several peripheral systems, including the reproductive, cardiovascular, and endocrine systems, although these roles are less well understood compared to its functions in the brain and gut.
- The production and regulation of serotonin are influenced by multiple factors, including diet, genetics, exposure to sunlight, physical activity, and stress levels. Since tryptophan is a precursor for serotonin, a diet rich in this amino acid—found in foods like turkey, eggs, cheese, and nuts—can support serotonin synthesis. Sunlight exposure also plays an important role, as it is thought to increase serotonin production, which is why seasonal affective disorder (SAD), a type of depression that occurs during the darker months, is linked to reduced sunlight and lower serotonin levels.
- Serotonin’s impact extends beyond just mood regulation; it also influences sleep by acting as a precursor to melatonin, the hormone that regulates circadian rhythms and sleep–wake cycles. The conversion of serotonin to melatonin occurs in the pineal gland, particularly in response to darkness, highlighting serotonin’s role in promoting restful sleep and aligning the body with the day–night cycle.
