Transient responses of melatonin to stress

Melatonin and its metabolites are ubiquitous antioxidants that are produced in response to reactive oxygen species (ROS) in virtually all cells of the body. The highest reported melatonin values in plasma and sweat occur during heavy exercise both indoors and outdoors during the day. The advent of sweat biosensors with sufficient melatonin sensitivity provides pseudo real-time evidence that melatonin is produced throughout the body not just in the pineal gland. The role of the pineal gland appears to be to provide cyclic production of melatonin for the regulation of circadian rhythms as well as supplemental melatonin during periods of low cellular activity.  Melatonin from the pineal gland represents only a small fraction of the body’s production capacity. Greater than 5 pg/ml min ramp rates for plasma and sweat melatonin have been reported during strenuous exercise in sunlight as compared to 0.15 pg/ml min ramp rates for plasma melatonin under dim light melatonin onset (DLMO) conditions.  Sunlight and exercise, like fever, generates transient elevated levels of ROS in tissues with time constants measured in minutes or even seconds making this systemic antioxidant response potentially protective. Based on a simple accounting of ROS generated by sunlight, ROS we breathe, ROS we drink, and exercise, it appears that the body maintains a heightened basal level of ROS as part of its pathogen defense mechanisms.  Current human lifestyles and modern enclosed spaces have substantially eliminated over 90% of the ROS which undermines one of the body’s primary defenses. With advanced age, the inability to maintain this protective barrier appears to make us more susceptible to disease.