Background: Melatonin synchronizes central but also peripheral oscillators (fetal adrenal
gland, pancreas, liver, kidney, heart, lung, fat, gut, etc.), allowing temporal organization of biological
functions through circadian rhythms (24-hour cycles) in relation to periodic environmental changes and
therefore adaptation of the individual to his/her internal and external environment. Measures of melatonin
are considered the best peripheral indices of human circadian timing based on an internal 24-hour clock.
Methods: First, the pharmacology of melatonin (biosynthesis and circadian rhythms, pharmacokinetics
and mechanisms of action) is described, allowing a better understanding of the short and long term effects
of melatonin following its immediate or prolonged release. Then, research related to the physiological
effects of melatonin is reviewed.
Results: The physiological effects of melatonin are various and include detoxification of free radicals and
antioxidant actions, bone formation and protection, reproduction, and cardiovascular, immune or body
mass regulation. Also, protective and therapeutic effects of melatonin are reported, especially with regard to
brain or gastrointestinal protection, psychiatric disorders, cardiovascular diseases and oncostatic effects.
Conclusion: This review highlights the high number and diversity of major melatonin effects and opens
important perspectives for measuring melatonin as a biomarker (biomarker of early identification of
certain disorders and also biomarker of their follow-up) and using melatonin with clinical preventive and
therapeutic applications in newborns, children and adults based on its physiological regulatory effects.