title: Multi-night exposure to 60 Hz magnetic fields: effects on melatonin and its enzymatic metabolite.
abstract: Magnetic field-induced suppression of nocturnal melatonin in humans has been reported in occupational and residential studies, but not in laboratory-based exposure studies. The present study examined whether this contrasting pattern of results might be related to associated differences in exposure duration or to field-induced measurement instability over time. Thirty healthy young men were evaluated using a randomized, double-blind test protocol. Statistical analysis indicated that 4 consecutive nights of exposure to power-frequency magnetic fields at occupational intensity (resultant flux density = 28.3 microtesla, muT, [283 milligauss, mG]) had no differential effect on concentrations of melatonin or its major enzymatic metabolite (6-hydroxymelatonin sulfate, 6-OHMS) in daily morning urine samples, compared to equivalent no-exposure sham control conditions. The consistency of intra-individual urinary measurements over the 4 test nights also was quite high (P < 0.01) in the sham control condition. In contrast, repeated nightly exposure to the magnetic field was associated with reduced consistency. Morning urinary measures obtained after exposure on night 4 differed (P < 0.01) from similar measures obtained after the second and third exposure night. Thus, while the overall results of this study do not support the melatonin hypothesis, there is some suggestion of a possible cumulative effect of magnetic field exposure on the stability of individual melatonin measurements over time. Additional research with longer periods of controlled exposure may be warranted.
authors.affiliation: Midwest Research Institute, Kansas City, Missouri, USA. cgraham@mriresearch.org
authors.forename: C
authors.initials: C
authors.lastname: Graham
authors.forename: M R
authors.initials: MR
authors.lastname: Cook
authors.forename: A
authors.initials: A
authors.lastname: Sastre
authors.forename: D W
authors.initials: DW
authors.lastname: Riffle
authors.forename: M M
authors.initials: MM
authors.lastname: Gerkovich
mesh_terms: D000293:Adolescent; D000328:Adult; D002940:Circadian Rhythm; D004311:Double-Blind Method; D004574:Electromagnetic Fields / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine*; D010870:Pineal Gland / Q000378:metabolism / Q000528:radiation effects*
chemical_list: C054513:6-sulfatoxymelatonin; D008550:Melatonin