Bioelectromagnetics 22:138^143 (2001)
Chronic Exposure to ELF Magnetic Fields
During Night SleepWith Electric Sheet: Effects
on Diurnal M e latoni n Rh ythms i n Men
Seung Cheol Hong,
1,3
Yoshika Kurokawa,
2
* Michino r i Kabuto,
2
and Ryutaro Ohtsuka
3
1
N atio na l Institute of En v iron m ental R esearch, Seoul, K o rea
2
N atio n a l Institute for E n vironmental Stud i es, Ibar ak i, Japan
3
Department of Human Ecology, University of Tokyo, Japan
The possible effects of repeated night-time exposure to an extremely low frequency magnetic ®eld
(ELF±MF) on melatonin were investigated in nine healthy male subjects aged 23±37 yr. The 16-
week experiment consisted of 3 weeks of pre-exposure, 11 weeks of night-time exposure to MF
generated from a nonheated electric sheet (ES), and 2 weeks of post-exposure recovery observation.
The average MF intensity (rms, mainly 50 Hz AC) on the surface of the sheet was 0.7 mT at the
head, 8.3 mT at the waist, and 3.5 mT at the feet 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
was determined, and 24 h rhythms were extracted for each subject and each experimental period
(pre-exposure, ®rst half and latter half exposure, and post-exposure periods) by the method of
complex cosine curve ®tting. Although estimates of the peak height, acrophase, and total daily
amount of melatonin were characterized by signi®cant variations among individual subjects, they
did not reveal any statistically signi®cant difference between exposure periods and nonexposure
periods. Thus, the present study indicates that any profound effect of the MF originating from an ES
on nocturnal melatonin production and its circadian rhythm is unlikely. Bioelectromagnetics
22:138±143, 2001.
ß 2001 Wiley-Liss, Inc.
Key words: AC magnetic ®eld; melatonin; human; circadian rhythm
INTRODUCTION
Nocturnal synthesis of melatonin in animals has
been reported to change due to exposure to ELF±MF
in some experiments [Reiter et al., 1988; Wilson et al.,
1989; Kato et al., 1994; Loscher et al., 1994; Yellon,
1994; Selmaoui and Touitou, 1995]. However, the
results of animal studies examining the in¯uence of
MF exposure have been inconsistent as a whole,
possibly re¯ecting differences in animal species or
physical characteristics of the generated ®elds, such as
polarization and intermittency. As for humans, Wilson
et al. [1990] reported that in the morning urine of some
but not all subjects, weak MF exposure via an electric
blanket (EB) for 8 weeks was related to lowered
nocturnal melatonin synthesis in terms of the total
amount of excreted melatonin metabolite (6-hydroxy-
melatonin sulfate, 6-OHMS). In a series of acute (one-
night) exposure experiments, Graham et al. [1996a,b]
found no signi®cant change in night-time melatonin
levels in sera by exposure to 60 Hz circularly-polarized
MF. Carrying out a similar experiment, Selmaoui et al.
[1996] could not ®nd any effect of a 50 Hz linearly-
polarized MF on melatonin in humans.
The present study evaluated the probability of
reported effects of repeated exposure to an MF
generated from an EB. It considered the diurnal
rhythms of melatonin and applied the complex cosine
curve ®tting method to the data obtained from
frequently collected urine specimens. A nonheated
electric sheet (ES), instead of EB, was used; and only
males participated in the study in order to prevent the
possible effects of body heating and the menstrual
ß 2001Wiley-Liss, Inc.
ÐÐÐÐÐÐ
Contract grant sponsor: National Institute for Environmental
Studies (NIES, Japan); Contract grant number: HS-14; Contract
grant sponsor: Sasagawa Health Science Foundation.
*Correspondence to: Yoshika Kurokawa, 16-2 Onogawa, Tsu-
kuba, Ibaraki 305-0053, Japan. E-mail: kurokawa@nies.go.jp
Received for review 8 January 1999; Final revision received 10
April 2000
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