Constant Pineal Output and Increasing Body Mass Account for Declining Melatonin Levels During Human Growth and Sexual Maturation

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Abstract
Twenty‐four‐h urine samples, divided into two fractions representing night‐ and daytime melatonin production, were collected from 115 healthy individuals between the ages of 3 and 80, of known height and weight, and assayed for 6‐hydroxy melatonin sulphate (SaMT), a major urinary metabolite of melatonin, by gas chromatography mass spectrometry. The population was divided for analytical purposes into children (boys aged 3–10.99, girls aged 3–9.59), adolescents (males aged 11–17.99, females aged 9.60–17.99), and adults (men and women over 18). The results showed approximately the same excretion over 24 h in all 3 groups but that the night/day ratio was considerably greater in children and adolescents compared to adults (P < 0.001). However, when the results were expressed as a function of body weight (BW), body surface area (BSA), or creatinine excretion (CE), nocturnal SaMT was higher in children than in adults (P < 0.001 for all 3 parameters) or adolescents (BW, P < 0.001; BSA, P < 0.002; CE, P < 0.001) and was higher in adolescents than in adults (BW and BSA, P < 0.001). Children also excreted more during the day than adults (BW, P < 0.01; CE, P < 0.001) or adolescents (BWαCE, P < 0.02). Our results show that pineal output barely changes during childhood and adolescence. However, there is an age related decrease in SaMT excretion/unit body mass which correlates with an age‐related increase in body mass. We therefore conclude that the decrease in circulating levels of melatonin during growth and sexual maturation is brought about by an increase in body mass.