CHANGES IN HUMAN PLASMA MELATONIN PROFILES IN RESPONSE TO 50 HZ MAGNETIC-FIELD EXPOSURE

The effects of power-frequency magnetic fields on nighttime plasma mel atonin were studied in a group of 30 adult male human subjects. Exposu re consisted of 20 mu T (200 mG) at 50 Hz (circularly polarized) at ce rtain times in relation to the predicted time of onset of rise in mela tonin concentration for a particular individual (the time of onset was predicted from a previous screening night). Response to this exposure was compared to sham-exposure (in random order). When exposure preced ed onset of rise, a significant delay in onset time relative to sham-e xposure of approximately half an hour was observed, with indications ( marginally significant) of a reduction in maximum melatonin level. Ana lysis of distribution of time-delays is consistent with two population s: those individuals who respond (around 20%) and those that do not. M agnetic fields generated by square-wave currents produce more marked r eductions in the maximum level when compared to sinusoidal waveforms, but there was no significant difference in onset time.