NIEHS-funded research showed that nighttime exposure to artificial light can stimulate the growth of breast tumors in mice by suppressing the levels of a key hormone called melatonin. Blood extracted from sleeping volunteers could actually prevent tumor growth in an animal model. Extended periods of nighttime darkness were shown to greatly slow the growth of these tumors. Blood from women whose sleep was interrupted lost much of its cancer-prevention ability. These results might explain why female night shift workers have a higher rate of breast cancer, and may offer an explanation for the rise in breast cancer incidence in industrialized countries.

Tags: breast cancer, women's health