Nocturnal excretion of a urinary melatonin metabolite among electric utility workers.
OBJECTIVE
The effects of 60-Hz magnetic field and ambient light exposures on the pineal hormone melatonin were studied among electric utility workers.


METHODS
Personal exposure was measured at 15-second intervals over 3 consecutive 24-hour periods. Exposure metrics based on magnetic field intensity, intermittence, or temporal stability were calculated for periods of work, home, and sleep. A rate-of-change metric (RCM) 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-hydroxymelatonin sulfate (6-OHMS) excretion and creatinine-adjusted nocturnal 6-OHMS (6-OHMS/cr) concentration were analyzed with adjustment for age, month, and light exposure.


RESULTS
Magnetic field intensity, intermittence, or cumulative exposure had little influence on nocturnal 6-OHMS excretion. 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 field exposures at home was associated with lower nocturnal 6-OHMS/cr and overnight 6-OHMS levels. Modest reductions in the mean 6-OHMS levels occurred after RCMS exposures during work. The greatest reductions occurred when RCMS exposures both at work and at home were combined; therefore the effects of temporally stable magnetic fields may be integrated over a large portion of the day.


CONCLUSIONS
Results from this study provide evidence that temporally stable magnetic field exposures are associated with reduced nocturnal 6-OHMS excretion in humans.
Department of Environmental Health, Colorado State University, Fort Collins 80523, United States.
J B
JB
Burch
J S
JS
Reif
M G
MG
Yost
T J
TJ
Keefe
C A
CA
Pitrat
D000328:Adult; D000704:Analysis of Variance; D015415:Biomarkers / Q000652:urine; D002940:Circadian Rhythm; D004560:Electricity; D004574:Electromagnetic Fields / Q000009:adverse effects*; D004784:Environmental Monitoring / Q000379:methods*; D006801:Humans; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine*; D008875:Middle Aged; D016273:Occupational Exposure / Q000009:adverse effects*; D012016:Reference Values; D017132:Workplace
D015415:Biomarkers; D008550:Melatonin; C012365:6-hydroxymelatonin