NOCTURNAL EXCRETION OF A URINARY MELATONIN METABOLITE AMONG ELECTRIC UTILITY WORKERS

Objectives The effects of 60-Hz magnetic field and ambient light expos ures on the pineal hormone melatonin were studied among electric utili ty workers. Methods Personal exposure was measured at 15-second interv als over 3 consecutive 24-hour periods. Exposure metrics based on magn etic field intensity, intermittence, or temporal stability were calcul ated for periods of work, home, and sleep. A rate-of-change metric (RC M) was used to estimate intermittence, and the standardized RCM (RCMS = RCM/standard deviation) was used to evaluate temporal stability. The effects of magnetic field exposure on total overnight 6-hydroxymelato nin sulfate (6-OHMS) excretion and creatinine-adjusted nocturnal 6-OHM S (6-OHMS/cr) concentration were analyzed with adjustment for age, mon th, and light exposure. Results Magnetic field intensity, intermittenc e, or cumulative exposure had little influence on nocturnal 6-OHMS exc retion. Residential RCMS magnetic field exposures were associated with lower nocturnal 6-OHMS/cr concentrations. In multivariate statistical analyses, the interaction term for geometric mean and RCMS magnetic f ield exposures at home was associated with lower nocturnal 6-OHMS/cr a nd overnight 6-OHMS levels. Modest reductions in the mean 6-OHMS level s occurred after RCMS exposures during work. The greatest reductions o ccurred when RCMS exposures both at work and at home were combined; th erefore the effects of temporally stable magnetic fields may be integr ated over a large portion of the day. Conclusions Results from this st udy provide evidence that temporally stable magnetic field exposures a re associated with reduced nocturnal 6-OHMS excretion in humans.