thymus, skeletal muscle, and reproductive system among others. Present in almost all body fluids, including amniotic fluid, breast milk, cerebrospinal fluid, feces, synovial fluid, saliva, and urine. Cells have melatonin receptors in the membrane, known as MT1 and MT2, and three nuclear receptors, ROR-alpha, -beta and -gamma. Two main organs produce melatonin: the pineal gland and the gut. Melatonin: Where is it found? Minich DM, Henning M, Darley C, Fahoum M, Schuler CB, Frame J. Is Melatonin the "Next Vitamin D"?: A Review of Emerging Science, Clinical Uses, Safety, and Dietary Supplements. Nutrients. 2022 Sep 22;14(19):3934. doi: 10.3390/nu14193934. PMID: 36235587; PMCID: PMC9571539. PMID: 35956837 Kvetnoy I, Ivanov D, Mironova E, Evsyukova I, Nasyrov R, Kvetnaia T, Polyakova V. Melatonin as the Cornerstone of Neuroimmunoendocrinology. Int J Mol Sci. 2022 Feb 6;23(3):1835. doi: 10.3390/ijms23031835. PMID: 35163757; PMCID: PMC8836571.