Geomagnetic activity and human melatonin metabolite excretion.

Elevated geomagnetic activity has been linked with human psychological, neurological and cardiovascular outcomes, and altered melatonin production has been implicated as an underlying mechanism to explain these effects. The relationship between geomagnetic activity and overnight excretion of the melatonin metabolite, 6-hydroxymelatonin sulfate (6-OHMS), was evaluated in a population of 153 male electric utility workers. The effect of geomagnetic activity combined with either 60Hz magnetic field or ambient light exposures was also evaluated. Elevated equivalent amplitudes (USGS, Boulder, CO) were associated with lower adjusted mean nocturnal 6-OHMS/cr concentrations and reduced total overnight 6-OHMS excretion, consistent with a previous study. Time intervals in which geomagnetic activity predicted the largest differences in mean 6-OHMS excretion generally occurred between 15- and 33-h prior to urine sample collection. These times coincide with key periods of melatonin regulation and production, respectively, suggesting that geomagnetic activity may play a role in the entrainment of human melatonin rhythms.