Reduced excretion of a melatonin metabolite in workers exposed to 60 Hz magnetic fields

The effects of occupational 60 Hz magnetic field and ambient light exposure s on the pineal hormone, melatonin,were studied in 142 male electric utilit y workers in Colorado, 1995-1996. Melatonin was assessed by radioimmunoassa y of its metabolite, 6-hydroxymelatonin sulfate (6-OHMS), in post-work shif t urine samples. Personal magnetic field and fight exposures were measured over 3 consecutive days using EMDEX C meters adapted with light sensors. Tw o independent components of magnetic field exposure, intensity (geometric t ime weighted average) and temporal stability (standardized rate of change m etric or RCMS), were analyzed for their effects on creatinine-adjusted 6-OH MS concentrations (6-OHMS/cr) after adjustment for age, month, and light ex posure. Geometric mean magnetic field exposures were not associated with 6- OHMS/cr excretion. Men in the highest quartile of temporally stable magneti c field exposure had fewer 6-OHMS/cr concentrations on the second and third days compared with those in the lowest quartile. Light exposure modified t he magnetic field effect. A progressive decrease in mean 6-OHMS/cr concentr ations in response to temporally stable magnetic fields was observed in sub jects with low workplace light exposures (predominantly office workers), wh ereas those with high ambient light exposure showed negligible magnetic fie ld effects. Melatonin suppression may be useful for understanding human bio logic responses to magnetic field exposures.