Melatonin

Melatonin is an indolamine hormone synthesised primarily by the pineal gland from serotonin in response to darkness. It is the principal endogenous signal of biological night, peaking 4-5 hours after lights-out and declining rapidly toward dawn. Endogenous production is suppressed by light exposure (particularly short-wavelength blue light), which is why screen use late in the evening can shift sleep onset later. Supplemental melatonin is one of the most-used sleep aids globally, available without prescription in the US and as a regulated medicine in much of Europe. Its evidence base is strongest for circadian-rhythm sleep disorders (jet lag, shift-work disorder, delayed sleep-phase syndrome) and for sleep onset in older adults whose endogenous melatonin production has declined. Effects in younger adults with primary insomnia are more modest. The popular consumer perception that more is better is wrong — physiologic doses of 0.3-1 mg often outperform the 5-10 mg products on store shelves, both for efficacy and because high doses produce supraphysiologic plasma levels that persist into the morning, causing next-day grogginess. Beyond sleep, melatonin is a potent free-radical scavenger and modulates immune function; its longevity-research interest stems from these antioxidant and anti-inflammatory effects.