Occupational magnetic field exposure and melatonin: Interaction with night-at-light
Tramčs per Klaus Rudolph (Citizens'
Department of Environmental Sciences, University of Kuopio,
70211 Kuopio, Finland.
We have recently reported interesting effects of 50-Hz magnetic fields
(MF) on the urinary excretion of 6-hydroxy melatonin sulfate (6-OHMS)
in CD2F1 mice (Kumlin et al., 2000). No natural light-regulated diurnal
Melatonin rhythm is seen in this mouse strain, but a consistent and statistically
significant day-night difference (higher levels at night) appeared in
animals continuously exposed to a 100-µT MF. A possible interpretation
of the finding is that MF exposure increases sensitivity of the pineal
gland to light (in this mouse strain normally insensitive to diurnal light
variations, the increased sensitivity would strengthen the natural melatonin
To test the hypothesis that MF exposure increases sensitivity to light
also in humans, we reanalyzed data from a study on 6-OHMS excretion in
women occupationally exposed (in a garment factory) to MFs (Juutilainen
et al., 2000)
Data from the questionnaire used by Juutilainen et al. (2000) were used
for dichotomous classification of the subjects with respect to exposure
to light-at-night. The questionnaire had direct questions on use of light
at night in the bedroom, lamps outside the bedroom window, and dark or
light curtains in the bedroom. The four-category MF exposure data from
Juutilainen et al. (2000) was dichotomized (exposure or no exposure).
One-way analysis of variance (ANOVA) of logarithmically transformed data
and Tukey's multiple comparison test were used for statistical analysis.
RESULTS AND DISCUSSION:
The lowest excretion of 6-OHMS was observed in the group of women who
were exposed to both MF and
light-at-night (Table 1). According to ANOVA, the differences between
the four groups were significant
(p<0.0001). According to Tukey's test, the group exposed to both MF
and night-at-light was significantly
different from all other groups. The effect of MF exposure was also significant
among the women who had no light exposure at night. The low number of
subjects who were exposed to both MF and light-at-night reduces the reliability
of the data. The results support the hypothesis that daytime occupational
exposure to MF enhances the effects of nighttime light exposure on melatonin
* Kumlin T, Heikkinen P, Laitinen J, Juutilainen J (2000) BEMS Twenty-Second
Annual meeting, Abstract Book, 282.
* Juutilainen J, Stevens RG, Anderson LE, Hansen NH, Kilpeläinen M, Kumlin
T, Laitinen JT, Sobel E, Wilson BW (2000) J Pineal Res 28:97-104.
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