Residential magnetic fields, light-at-night, and nocturnal urinary 6-sulfatoxymelatonin concentration in women

Exposure to 60-Hz magnetic fields may increase breast cancer risk by suppre ssing the normal nocturnal rise in melatonin. This 1994-1996 Washington Sta te study investigated whether such exposure was associated with lower noctu rnal urinary concentration of 6-sulfatoxymelatonin in 203 women aged 20-74 years with no history of breast cancer. Each woman was interviewed and prov ided data on the following for a 72-hour period at two different seasons of the year: 1) magnetic field and ambient light measured every 30 seconds in her bedroom, 2) personal magnetic field measured at 30-second intervals, a nd 3) complete nighttime urine samples on three consecutive nights. Lower n octurnal urinary 6-sulfatoxymelatonin level was associated with more hours of daylight, older age, higher body mass index, current alcohol consumption , and current use of medications classified as beta blockers, calcium chann el blockers, or psychotropics. After adjustment for these factors, higher b edroom magnetic field level was associated with significantly lower urinary concentration of 6-sulfatoxymelatonin during the same night, primarily in women who used these medications and during times of the year with the fewe st hours of darkness. These results suggest that exposure to nighttime resi dential 60-Hz magnetic fields can depress the normal nocturnal rise in mela tonin.