Chronome assessment of circulating melatonin in humans

Background. Melatonin (MEL) production occurs mainly during the dark span. A prominent circadian variation is demonstrated in both blood and urine in humans. Materials and methods: The circadian, circannual, age and gender patterns of MEL were concomitantly investigated in 40 men and 132 women, each providing blood samples every 4 hours for 24 hours for conventional and cosinor analysis. Results. Circulating MEL is circadian periodic (P < 0.001), peaking at night. The MESOR (rhythm-adjusted mean) is higher in women than in men. The circadian amplitude decreases with age. Both are modulated by a circannual variation, the MESOR peaking in winter (P < 0.001) and the circadian amplitude in summer (P < 0.05). Conclusions. Samples, unqualified as to gender, age and/or season, incompletely characterize the circadian MEL patterns. This chronome approach detects changes that may escape detection otherwise, checking whether a value is too high or too low, and also whether 'swinging' occurs to the right extent.