Tuesday, December 20, 2005

Artificial Light, Melatonin, and Breast Cancer

A recent study has shown that human breast tumors are stimulated to grow by the reduction in melatonin caused by exposure to artificial light. The results are consistent with the higher level of breast cancer found in industrialized nations (with lots of artificial light) than in less developed countries, and even higher in female night shift workers.
"We know that many tumors are largely dependent on a nutrient called linoleic acid, an essential fatty acid, in order to grow," said David Blask, M.D., Ph.D., a neuroendocrinologist with the Bassett Research Institute and lead author on the study. "Melatonin interferes with the tumor's ability to use linoleic acid as a growth signal, which causes tumor metabolism and growth activity to shut down."
A caveat is that this study was done with human breast tumor cells growing in rats, not humans. Confirmation of the effect in humans could have far reaching consequences.
"If the link between light exposure and cancer risk can be confirmed, it could have an immediate impact on the production and use of artificial lighting in this country," said Blask. "This might include lighting with a wavelength and intensity that does not disrupt melatonin levels and internal timekeeping."

"Day workers who spend their time indoors would benefit from lighting that better mimics sunlight," added Blask. "Companies that employ shift workers could introduce lighting that allows the workers to see without disrupting their circadian and melatonin rhythms."
The research was published in the December 1 issue of Cancer Research.

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