aMT6s

aMT6s, also known as 6-sulfatoxymelatonin, is the major urinary metabolite of melatonin and is widely used as a biomarker of endogenous melatonin production. It provides an integrated measure of nocturnal melatonin secretion and is commonly used in sleep and circadian research.

Biochemical basis and metabolism: Melatonin is metabolized in the liver first by hydroxylation to 6-hydroxymelatonin, and then by sulfate conjugation to form 6-sulfatoxymelatonin, which is excreted in urine. Because it reflects the overall overnight melatonin production, aMT6s levels in urine are influenced by circadian phase, light exposure, and endogenous synthesis.

Measurement and interpretation: aMT6s is typically measured in urine samples, often as an overnight collection or in the first-morning void. Assays commonly employ immunoassay techniques or more specific methods such as liquid chromatography–mass spectrometry. Results are frequently normalized to creatinine to account for urine concentration. In general, higher overnight urinary aMT6s indicates greater nocturnal melatonin production, while lower levels suggest reduced melatonin secretion.

Applications and considerations: Researchers use aMT6s to assess circadian phase and amplitude, investigate the effects of light exposure, shift work, aging, and sleep disorders, and explore potential links between melatonin signaling and health outcomes. Limitations include variability due to renal function, hydration status, and urine collection duration, as well as the fact that aMT6s reflects cumulative excretion rather than instantaneous blood melatonin levels. Interpretations should consider individual factors such as age, medications, and health status.