Could the humble light bulb play a role in the development of cancer? That’s the implication of a growing body of evidence that links breast cancer risk with exposure to artificial light. Two recent studies led by research associate Erin Flynn-Evans and her colleagues at the Division of Sleep Medicine at Brigham and Women’s Hospital provide further insight. The first study looked at 1,392 blind women with either little or no ability to perceive light; 66 had been diagnosed with breast cancer. After controlling for other risk factors, the researchers found that women with no light perception had a more than 50 percent reduction in breast cancer risk compared to those who could see some light.
A related study showed that the women with no light perception had their first menstrual period at a younger age than those with some light perception. The findings were surprising, Evans says, since earlier menarche is associated with increased odds of breast cancer in sighted women. Taken together, these findings suggest that reproductive differences aren’t responsible for the lower breast cancer risk observed in blind women. Further research is needed on the effects of artificial light on cancer development.