* Occupational magnetic field exposure and melatonin: Interaction with night-at-light (14/7/02)

Tramčs per Klaus Rudolph (Citizens' Initiative Omega)

J. Juutilainen
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 rhythm).


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.


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  production.


* 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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