Melatonin

Melatonin is a neurohormone primarily secreted by the pineal gland in response to darkness. Known as the 'hormone of darkness,' it acts as a systemic chronobiotic signal that informs the body's tissues of the time of day, coordinating the circadian rhythm. Beyond its role in sleep, melatonin is a potent endogenous antioxidant and immunomodulator that can cross the blood-brain barrier and protect mitochondria from oxidative stress.