The study results might explain why female night shift workers have a higher rate of breast cancer. It also offers a promising new explanation for the epidemic rise in breast cancer incidence in industrialized countries like the United States.

The National Cancer Institute and the National Institute of Environmental Health Sciences, agencies of the federal National Institutes of Health, provided funding to researchers at the Bassett Research Institute of the Mary Imogene Bassett Hospital in Cooperstown, New York and The Thomas Jefferson University in Philadelphia, Pa. The results are published in the December 1, 2005 issue of the scientific journal Cancer Research.

"This is the first experimental evidence that artificial light plays an integral role in the growth of human breast cancer," said NIEHS Director David A. Schwartz, M.D. "This finding will enable scientists to develop new strategies for evaluating the effects of light and other environmental factors on cancer growth."

"The risk of developing breast cancer is about five times higher in industrialized nations than it is in underdeveloped countries," said Les Reinlib, Ph.D., a program administrator with the NIEHS' grants division. "These results suggest that the increasing nighttime use of electric lighting, both at home and in the workplace, may be a significant factor."

Previous research showed that artificial light suppresses the brain's production of melatonin, a hormone that helps to regulate a person's sleeping and waking cycles. The new study shows that melatonin also plays a key role in the development of cancerous tumors.

"We know that many tumors are
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Contact: John Peterson
peterso4@niehs.nih.gov
919-541-7860
NIH/National Institute of Environmental Health Sciences
19-Dec-2005