Melatonin Production

AANAT codes for the enzyme that converts serotonin into N-acetylserotonin, and ASMT codes for the enzyme that converts N-acetylserotonin into melatonin. The two-step pathway runs in the pineal gland at night and is sharply suppressed by even moderate light exposure.

Carriers of common AANAT and ASMT reduced-activity variants are associated with lower nighttime melatonin production, and may experience longer sleep onset, lighter sleep, or seasonal mood changes related to winter light scarcity. Carriers of higher-function variants tend to produce robust melatonin rhythms on default light exposure.

Serotonin is the upstream substrate, which is why tryptophan-rich evening meals and adequate B6 status both support endogenous melatonin synthesis. Bright morning light increases nighttime melatonin output (the body anchors the dark-period production to the strength of the prior light period). Even brief evening light exposure (60–90 minutes of bright indoor lighting) suppresses melatonin synthesis by 50–90%.

Standard sleep advice focuses on melatonin supplementation; the upstream lever (protecting the body’s own production) moves the needle for more clients. Which AANAT/ASMT variant pattern you carry decides whether the focus belongs on supplementing or on protecting endogenous synthesis through morning light and evening dim.