Residential Magnetic Fields, Light-at-Night, and Nocturnal Urinary 6

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  • 591

    American Journal of

    EPIDEMIOLOGYCopyright 2001 by the Johns Hopkins University

    Bloomberg School of Public Health

    Sponsored by the Society for Epidemiologic Research

    Published by Oxford University Press

    Volume 154

    Number 7

    October 1, 2001

    Magnetic Fields, Light-at-Night, and Melatonin Davis et al.ORIGINAL CONTRIBUTIONS

    Residential Magnetic Fields, Light-at-Night, and Nocturnal Urinary 6-Sulfatoxymelatonin Concentration in Women

    Scott Davis,1,2 William T. Kaune,3 Dana K. Mirick,1 Chu Chen,1 and Richard G. Stevens4

    Exposure to 60-Hz magnetic fields may increase breast cancer risk by suppressing the normal nocturnal risein melatonin. This 19941996 Washington State study investigated whether such exposure was associated withlower nocturnal urinary concentration of 6-sulfatoxymelatonin in 203 women aged 2074 years with no historyof breast cancer. Each woman was interviewed and provided data on the following for a 72-hour period at twodifferent 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, and 3) complete nighttime urine samples on threeconsecutive nights. Lower nocturnal urinary 6-sulfatoxymelatonin level was associated with more hours ofdaylight, older age, higher body mass index, current alcohol consumption, and current use of medicationsclassified as beta blockers, calcium channel blockers, or psychotropics. After adjustment for these factors, higherbedroom 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 ofthe year with the fewest hours of darkness. These results suggest that exposure to nighttime residential 60-Hzmagnetic fields can depress the normal nocturnal rise in melatonin. Am J Epidemiol 2001;154:591600.

    breast neoplasms; carcinogens, environmental; circadian rhythm; electricity; electromagnetic fields; melatonin

    Received for publication July 6, 2000, and accepted for publica-tion December 20, 2000.

    Abbreviation: BMI, body mass index.1 Program in Epidemiology, Division of Public Health Sciences,

    Fred Hutchinson Cancer Research Center, Seattle, WA.2 Department of Epidemiology, School of Public Health and

    Community Medicine, University of Washington, Seattle, WA.3 EM Factors, Richland, WA.4 Department of Community Medicine, University of Connecticut

    Health Center, Farmington, CT.Reprint requests to Dr. Scott Davis, Fred Hutchinson Cancer

    Research Center, 1100 Fairview Avenue North MP-474, P.O. Box19024, Seattle, WA 98109-1024 (e-mail: sdavis@fhcrc.org).

    It has been suggested that exposure to 60-Hz magneticfields may increase the risk of breast cancer by suppressingthe normal nocturnal rise in melatonin production andrelease (1), thereby resulting in increased levels of circulat-ing estrogen. Several lines of inquiry have been pursued toinvestigate a possible link between pineal function, circulat-ing estrogen level, and breast cancer risk (summarized byStevens and Davis and by Brainard et al. (2, 3)). Other thanlimited evidence that blood melatonin levels are reduced inhuman volunteers exposed to magnetic fields (4), there have

    been few studies of the effect of magnetic field exposure onpineal function in humans. Although some results fromexperimental and occupational studies suggest that nocturnalmelatonin levels can be reduced by exposure to magneticfields, the evidence thus far is inconsistent and incomplete(510). More importantly, it remains unknown whether suchexposures can alter the endogenous hormonal environmentin women in a manner that might be important in the etiol-ogy of breast cancer. Therefore, the present study wasundertaken in 19941996 to investigate, for the first knowntime in women, whether exposure to magnetic fields and/orlight-at-night is associated with lower nocturnal concentra-tion of the primary metabolite of melatonin found in theurine (6-sulfatoxymelatonin).

    MATERIALS AND METHODS

    Study participants

    Participants were women aged 2074 years selected froma group of 591 women in King and Snohomish counties inWashington State who participated as controls in a case-control study of breast cancer and exposure to electromag-

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  • 592 Davis et al.

    Am J Epidemiol Vol. 154, No. 7, 2001

    netic fields (11). The women initially were identified by ran-dom digit dialing (12). A sample was selected to provideapproximately equal representation of the highest and low-est bedroom magnetic field exposures. Of the 31 womenstill living in homes classified as Very High CurrentConfiguration according to the scheme developed byWertheimer and Leeper (13) to approximate exposuresinside a residence on the basis of external wiring configura-tions, 26 (84 percent) agreed to participate. Each of theremaining 556 potentially eligible women was ordered bythe mean magnetic field level measured in her bedroom overa 48-hour continuous period during her participation in thecase-control study. Eighty-three (82 percent) of the 101 eli-gible women who had the highest measured exposures and94 (85 percent) of the 110 eligible women who had the low-est measured exposures agreed to participate. The institu-tional review board approved the protocol for contactingpotential participants and the manner in which informedconsent was obtained.

    Data collection and laboratory methods

    Data collection consisted of the elements described intable 1 for a 72-hour measurement period. The entire proto-col was repeated approximately 3 or 6 months later, basedon random assignment, to provide measurements in differ-ent seasons of the year. This study design made it possibleto investigate the effects of different lengths of daily dark-ness on any potential association between magnetic field

    exposure and urinary 6-sulfatoxymelatonin level. The studytook place over approximately 14 months.

    The volume of urine was determined, and each samplewas assayed for creatinine concentration based on a kineticmodification of the Jaffe reaction using the Roche Reagentfor Creatinine (Roche Diagnostic Systems, Nutley, NewJersey). Urinary concentrations of the primary metabolite ofmelatonin, 6-sulfatoxymelatonin, were determined by usingcommercially available radioimmunoassay kits (CIDtechResearch Inc., Mississauga, Ontario, Canada). The assaywas run in duplicate with 500 l of diluted sample. Each runincluded the kit control provided by the manufacturer and anin-house control using a urine sample provided by a volunteer at the beginning of the study was used. Assay sen-sitivity was 0.5 ng/ml urine, and intra- and interassay per-cent coefficients of variation were approximately 9 and 13percent, respectively.

    Statistical methods

    Nine exposure variables were defined prior to analysis tocharacterize a participants exposure to magnetic fields. Thefollowing three reflected exposure to magnetic fields in thebedroom at night: 1) mean nighttime bedroom magneticfield exposure, 2) proportion of nighttime bedroom mag-netic field measurements 0.2 T, and 3) short-term vari-ability in the bedroom magnetic field. Nighttime wasdefined for each subject and each night as the time periodbetween the last void before going to bed and the first void

    TABLE 1. Data elements studied to determine a possible association between exposure to magneticfields and/or light-at-night and urinary 6-sulfatoxymelatonin concentration, Washington State, 19941996

    In-person interview

    Personal magnetic field exposure*

    Bedroom magnetic field exposure*

    Ambient light*

    Urine sample

    Protocol adherence form

    Patterns of electric blanket useCurrent medication useUpdate of personal habits since case-control study

    EMDEX Lite meterBroadband (40800 Hz) x, y, and z orthogonal components of

    fieldMeasurements at 30-second intervals on a 24-hour basisDiary of activities in 30-minute time segments

    EMDEX II meterBroadband (40800 Hz) and harmonics (100800 Hz)Measurements at 30-second intervals during the nightMeter placed on floor near head of bed where magnetic field

    is within 0.05 T of field on pillow

    Commercial light sensorMeasured at 30-second intervals at head of bed during the night

    Complete nighttime urine sample on 3 consecutive nights

    Documented subjects night and any problems with urinecollection

    Element Description

    * All meters were calibrated prior to the start of the study and periodically on a regular basis thereafter. Enertech Consultants, Campbell, California. Graseby Electronics, Orlando, Florida. Participants were instructed to void their bladder just prior to retiring; any urine excreted after that time,

    including the first morning void just after rising, was collected.

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    the next morning. Mutually exclusive 10-minute timeblocks were used to group exposure measurements. A statis-tic (Y) was computed to characterize short-term variabilityin the bedroom magnetic field, as follows:

    where Bk, k = 1, 2, , 20 are the 20 values of the measuredmagnetic field recorded at 30-second intervals during a 10-

    minute time period. This statistic, when divided by (i.e., the number of measurement intervals 1), is equal tothe rate-of-change metric introduced by Yost (14). Thebedroom variability statistic was defined as the average ofall 10-minute Y statistics during the nighttime period.

    Three variable