Chronic exposure to 2.9 mT, 40 Hz magnetic field reduces melatonin concentrations in humans

Diurnal rhythm of serum melatonin concentrations was estimated in 12 men wi th low back pain syndrome before and after exposure to a very low-frequency magnetic field (2.9 mT, 40 Hz, square wave, bipolar). Patients were expose d to the magnetic field for 3 weeks (20 min per day, 5 days per week) eithe r in the morning (at 10:00 hr) or in the late afternoon (at 18:00 hr). Sign ificant depression in nocturnal melatonin rise was observed regardless of t he time of exposure. This phenomenon was characteristic for all the subject s, although the percent of inhibition of melatonin secretion varied among t he studied individuals.