Chronic exposure to ELF magnetic fields during night sleep with electric sheet: Effects on diurnal melatonin rhythms in men

The possible effects of repeated night-time exposure to an extremely low fr equency magnetic field (ELF-MF) on melatonin were investigated in nine heal thy male subjects aged 23-37 yr. The 16-week experiment consisted of 3 week s of pre-exposure, 11 weeks of night-time exposure to MF generated from a n onheated electric sheet (ES), and 2 weeks of post-exposure recovery observa tion. The average MF intensity (rms, mainly 50 Hz AC) on the surface of the sheet was 0.7 muT at the head, 8.3 muT at the waist, and 3.5 muT at the fe et of the subject. For each of the urine samples collected 5 times a day on scheduled sampling days, the urinary excretion rate (ng/h) of melatonin wa s determined, and 24 h rhythms were extracted for each subject and each exp erimental period (pre-exposure, first half and latter half exposure, and po st-exposure periods) by the method of complex cosine curve fitting. Althoug h estimates of the peak height, acrophase, and total daily amount of melato nin were characterized by significant variations among individual subjects, they did not reveal any statistically significant difference between expos ure periods and nonexposure periods. Thus, the present study indicates that any profound effect of the MF originating from an ES on nocturnal melatoni n production and its circadian rhythm is unlikely. Bioelectromagnetics 22:1 38-143, 2001. (C) 2001 Wiley-Liss, Inc.