A New York researcher says frequent exposure to artificial light at night may increase the risk of breast cancer.
In a study reported in the current issue of the American Journal of Epidemiology, Dr. Cristina Leske of Stony Brook University questioned 576 Long Island women who developed breast cancer, and 585 who never had the disease, to determine whether exposure to artificial light plays a role, Newsday reported.
A subset of women who had developed breast cancer tended to wake up frequently during the night and turned on lights during what should have been hours set aside for sleeping, Leske said.
At night, the hormone melatonin streams into the bloodstreams and flows throughout the night, suppressing cancer cells. Melatonin is switched off -- and estrogen switches on -- by the presence of light.
Leske concluded that the positive association of night lights with breast cancer was 65 percent. However, among overnight shift workers, Leske found a 45 percent lower breast cancer risk.
She said the results suggest that shift workers somehow altered their circadian clocks, so their hormone flow adapted to their work schedules, the newspaper reported.
Copyright 2006 by United Press International
Explore further: Four tobacco makers accused by French anti-smoking of collusion