Questions and Answers About EMF Electric and Magnetic Fields Associated with the Use of Electrical Power.
January 1995.

Biological Studies

Q. What about effects of EMFs on the hormone melatonin?

A. Melatonin is a hormone produced mainly at night by the pineal, a small gland in the brain. One reason scientists are interested in melatonin is that it could help explain results of some EMF epidemiological studies. Melatonin has been reported to slow the growth of some cancer cells, including breast cancer cells, in laboratory experiments. If power-frequency EMF can affect melatonin in humans, this could be a mechanism to explain results of some EMF studies of breast cancer.

In the 1980s, scientists found that in the rats exposed to 60-Hz electric fields, nighttime melatonin levels were reduced. Other studies have since reported that both AC and DC magnetic fields can also affect melatonin levels in rats and hamsters. Theses experiments are very delicate and depend on a combination of factors such as age of the animals and length of day. Melatonin levels were not affected in sheep raised for nearly a year in EMFs directly beneath a 500-kV transmission line. Experiments with baboons also showed no changes in melatonin. The Midwest Research Institute (MRI) has studied the effect of 60-Hz magnetic field exposure on human melatonin. In 1993 MRI reported that although subjects showed no effect on the average, those individuals with naturally lower levels of melatonin did show a small further decrease. However, in 1994 MRI reported that a second study, specifically designed to replicate the earlier results, found no such effect.