To evaluate the relationship between geomagnetic activity and overnight excretion of the melatonin metabolite, 6-hydroxymelatonin sulfate, and potential modifications by ambient light and 60 Hz MF exposure among male electric utility workers.
61 participants worked in the field of electric power distribution, 51 worked in electric generation and 41 were comparison workers. Collected data on total noctural urine output from 1997 and 1995 were analysed. Geomagnetic activity, 60 Hz magnetic field and ambient light exposures were summerized over 3 h, 24 h and 36 h intervals.
Elevated geomagnetic activity was associated with reduced melatonin metabolite excretion. There was no combined effect of 60 Hz magnetic field exposure with geomagnetic activity. There was little evidence for the combination of low ambient light exposures and elevated geomagnetic activity being associated with reduced 6-hydroxymelatonin sulphate levels. Time intervals in which geomagnetic activity predicted the largest differences in 6-hydroxymelatonin sulphate excretion occurred between 15 and 33 h prior to urine sample collection, which coincides with key periods of melatonin regulation.
The authors suggest that geomagnetic activity may play a role in the entrainment of human melatonin rhythm.