THE MELATONIN HYPOTHESIS - ELECTRIC-POWER AND BREAST-CANCER

Breast cancer is a disease of modern life. As societies industrialize, risk increases, yet it is unclear which of the myriad changes coming with industrialization drives this increase. One important hallmark of modem life is the pervasive use of electric power. Electric power pro duces light at night (LAN) and electric and magnetic fields (EMF), eit her or both of which may alter pineal function and its primary hormone melatonin, thereby, perhaps increasing the risk of breast cancer. Thi s hypothesis, stated a decade ago, is now receiving considerable exper imental and epidemiological attention. The circumstantial case for the hypothesis has three aspects: light effects on melatonin, EMF effects on melatonin, and melatonin effects on breast cancer. The strongest o f these aspects is the effects of light on melatonin. It is clear that the normal nocturnal melatonin rise in humans can be suppressed by li ght of sufficient intensity. The evidence for an effect of melatonin o n breast cancer in experimental animals is strong, but the evidence in humans is scant and difficult to gather. The weakest aspect of the ci rcumstantial case is EMF effects on melatonin. Whereas a half dozen in dependent laboratories have published findings of suppression in anima ls, there are inconsistencies, and there are no published data on huma ns. The direct evidence bearing on the hypothesis is sparse but provoc ative. Two laboratories have published data showing substantial increa ses in chemically induced breast cancer in rats by a weak AC (alternat ing current) magnetic field. The epidemiological evidence is very limi ted but has offered some support as well. An effect of electric power on breast cancer would have profound implications, and this possibilit y deserves continued investigation.