Melatonin

Overview

Melatonin is a hormone produced by the pineal gland in the brain and serves as the primary chemical signal that tells the body night has arrived. Secretion begins in the evening as light levels drop (an event called dim-light melatonin onset, or DLMO), peaks between 2:00 and 4:00 a.m., and is rapidly suppressed by morning light exposure. It is the central hormonal regulator of the circadian sleep-wake cycle.

Light and Suppression

Melatonin secretion is strongly suppressed by light, especially blue light near 480 nm. Using smartphones or computers in the two hours before bedtime has been shown experimentally to reduce melatonin output by up to 50% and delay sleep onset by more than 30 minutes. Conversely, bright light exposure in the morning rapidly halts melatonin production and promotes alertness.

Jet Lag Applications

Exogenous melatonin (supplements), taken at the right time, can help shift the body clock toward a new time zone. For eastbound travel, a dose of 0.5 to 3 mg taken about 30 minutes before the destination's bedtime accelerates the forward shift of the circadian clock. However, incorrect timing can push the clock in the wrong direction, so effective use requires an understanding of circadian phase. Melatonin is available over the counter in the United States, though in Japan it is not sold as a general supplement.