Effects of 50 Hz magnetic fields on human physiology: plasma melatonin levels

Plasma melatonin levels have been measured throughout the evening and night in a group of 30 male volunteers in response to a single exposure of 50 Hz magnetic fields for a few hours. Those exposed before the start of the evening rise in melatonin show a significant delay in this rise compared to controls. Some individuals show consistent delays in repeated trials. In a separate experiment, an individual who received exposures on successive days showed a progressive diminution of melatonin levels over subsequent nights. These findings are in accordance with the notion that magnetic fields encountered in the workplace may affect biological rhythms.