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Artificial Light Stimulates Breast Cancer

January 2006

NIH-funded research shows nighttime exposure to artificial light stimulates the growth of human bcreast tumors by suppressing melatonin, a key hormone that regulates sleep.

NIEHS and NCI funded the study, which was conducted by researchers at Bassett Research Institute at the Mary Imogene Bassett Hospital in Cooperstown, N.Y., and the Thomas Jefferson University in Philadelphia. The study appears in the Dec. 1 issue of Cancer Research, and links melatonin levels to the development of cancerous tumors.

As part of the study, researchers injected human breast cancer cells into lab mice. Once the cells developed into tumors, the tumors were implanted into female rats. Meanwhile, researchers collected blood samples from 12 healthy, premenopausal women during three different time frames - daytime; nighttime after two hours of darkness; and nighttime after 90 minutes of exposure to bright florescent light. The blood samples were then pumped directly through the developing tumors, enabling researchers to conclude that melatonin suppressed tumor development and growth.

DERT grants administrator at NIEHS, Les Reinlib, said the risk of developing breast cancer is about five times higher in industrialized nations, suggesting the increasing use of artificial lighting at night is a significant factor.

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