PREDICTION OF NOCTURNAL PLASMA MELATONIN FROM MORNING URINARY MEASURES

A growing literature indicates that blood levels of the hormone melato nin may have important implications for human health and wellbeing. Me latonin is synthesized and released into the general circulation at ni ght, however, and it is seldom feasible to draw blood samples at night in epidemiological studies. These is some evidence that levels of uri nary melatonin and of 6-sulfatoxymelatonin (aMT6s), the major metaboli te of melatonin, accurately reflect nocturnal plasma melatonin. if thi s is the case, urinary assays could be powerful tools for epidemiologi cal studies. A laboratory-based study was performed to examine the rel ationships between nocturnal plasma melatonin, morning urinary melaton in, and morning urinary aMT6s levels in 78 men. The relationship betwe en total nocturnal plasma melatonin and both urinary aMT6s corrected f or creatinine and urinary melatonin is significant. Combining the two urinary measures accounts Ear 72% of the variance in total plasma mela tonin. Peak nocturnal plasma melatonin also was significantly related to urinary melatonin and to aMT6s, The urinary measures show good sens itivity and specificity in identifying individual differences in noctu rnal plasma melatonin levels. These results support the inclusion of m orning urine samples to assess the contribution of the hormone melaton in in occupational or residential studies involving healthy, young men .