General Summary
Collective scientific data indicate that probiotics support intestinal serotonin secretion through multiple mechanisms: activating serotonin-synthesizing enzymes (particularly Tph1), balancing gut microbiota, reducing inflammation in the gut and brain, and amplifying serotonin signaling toward the brain. These processes not only improve digestion but also produce positive effects on mental health, including reduced anxiety and depression and improved sleep quality. Probiotic strains such as Bifidobacterium breve and Lactobacillus plantarum play key roles in this process. Clinical findings support the use of probiotics as a safe adjunctive therapy to enhance overall health.
1. Probiotics and Serotonin Biosynthesis in the Gut
Numerous modern scientific studies have demonstrated that probiotics can promote serotonin production in the intestine by activating serotonin-synthesizing enzymes, especially Tryptophan hydroxylase-1 (Tph1). Serotonin acts as an essential hormone and neurotransmitter that regulates intestinal motility and influences mood and cognition through the gut–brain axis. A review by Akram et al. (2023) indicated that probiotics enhance serotonin signaling, affecting several key physiological processes such as mood regulation and cognition. The study also observed that intestinal serotonin improves nutrient absorption and storage while modulating gut microbiota composition (Akram et al., 2023, pp. 1–12). [1][2]
2. Impact of Gut Serotonin on Mental Health
Serotonin produced in the gut is closely linked to brain function and mental state. Increased intestinal serotonin levels can help improve symptoms of depression and anxiety by regulating inflammatory responses and enhancing serotonin signaling to the brain. A study by Bistas et al. (2023) found that probiotics reduce the kynurenine/tryptophan ratio, increase the amount of tryptophan available for serotonin synthesis, and thus improve depression scores on the BDI scale (Bistas et al., 2023, pp. 5–9). Other evidence also shows that probiotics can reduce neuroinflammation and peripheral inflammation, thereby alleviating psychiatric symptoms (Dacaya et al., 2025). [3][4]
3. Key Probiotic Strains Supporting Serotonin Production
Several probiotic strains play significant roles in promoting serotonin biosynthesis, such as Bifidobacterium breve, Lactobacillus plantarum, and Bacillus species. These strains stimulate the expression of the Tph1 enzyme gene, enhance serotonin synthesis, and improve mood, cognitive function, and sleep quality. Reference indicates that probiotics enhance serotonin (5-hydroxytryptamine, 5-HT) formation. Specifically, section “3.1.1 Neurotransmitters” of that reference describes that strains like Lactobacillus and Bifidobacterium can regulate tryptophan metabolism and hydroxytryptamine (5-HT) synthesis—namely serotonin—through the gut–microbiota–brain axis. Preclinical studies and patents reveal that probiotic intake significantly increases serotonin levels in blood and brain tissues in animal models, while reducing anxiety- and depression-like behaviors. Certain strains, such as Bifidobacterium breve CCFM1025, also elevate levels of the serotonin precursor 5-hydroxytryptophan (5-HTP), promoting serotonin synthesis in the cortex. These findings indicate that probiotics can positively influence mood by stimulating serotonin biosynthesis and modulating the central nervous system. [5][6]
4. Mechanisms via the Gut–Brain Axis
Probiotics regulate serotonin production by balancing gut microbiota, reducing cytokine-producing inflammatory cells, and modulating neural signaling to the brain. Serotonin-synthesizing enzymes such as Tph1 are activated, while probiotics concurrently decrease inflammation in both the gut and the brain, thereby improving brain functions such as emotional regulation and reducing anxiety and depression (Akram et al., 2023; Dacaya et al., 2025). [4][1]
5. Clinical Benefits of Probiotics for Mental Health
Human clinical trials have shown that probiotic supplementation significantly reduces symptoms of anxiety and depression, as well as improves sleep quality among both healthy individuals and psychiatric patients. Probiotics are considered a safe solution with fewer side effects than conventional medications (Nature Communications, 2025). Research also notes that probiotics elevate peripheral tryptophan levels, contributing to enhanced mental health (Kumar et al., 2024). [5][7][8]
REFERENCES ANALYZED
1. Akram N. et al. (2023). Exploring the serotonin–probiotics–gut health axis. Food Science. https://pmc.ncbi.nlm.nih.gov/articles/PMC10867509/
2. Bistas K.G. et al. (2023). The Benefits of Prebiotics and Probiotics on Mental Health. Nutrients. https://pmc.ncbi.nlm.nih.gov/articles/PMC10490379/
3. Dacaya P. et al. (2025). Exploring neurotransmitter regulation following probiotics. ScienceDirect. https://www.sciencedirect.com/science/article/pii/S0899900725002096
4. Kumar A. et al. (2024). Probiotics as modulators of gut-brain axis for cognitive development. Frontiers in Pharmacology. https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2024.1348297/full
5. Katerina V. et al. (2025). Probiotics reduce negative mood over time: the value of daily self-reports in detecting effects. Nature Communications. https://www.nature.com/articles/s44184-025-00123-z
6. A. A. de Lima et al. (2025). Probiotics as technological innovations in psychiatric disorders: patents and research reviews. Frontiers in Nutrition. https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2025.1567097/full
ADDITIONAL REFERENCES
7. Yong S.J. et al. (2020). Antidepressive Mechanisms of Probiotics and Their Therapeutic Potential. Frontiers in Neuroscience. https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2019.01361/full
8. Loh J.S. et al. (2024). Microbiota–gut–brain axis and its therapeutic applications. Signal Transduction and Targeted Therapy. https://www.nature.com/articles/s41392-024-01743-1
9. Everett B.A. et al. (2022). Toward manipulating serotonin signaling via the microbiome. Neuropharmacology. https://www.sciencedirect.com/science/article/pii/S0958166922001604
10. Wright S. et al. (2025). Precision Psychobiotics for Gut–Brain Axis Health. Wiley Online Library. https://onlinelibrary.wiley.com/doi/10.1111/1751-7915.70079