Micrograph showing a lymph node invaded by ductal breast carcinoma, with extension of the tumour beyond the lymph node. Credit: Nephron/Wikipedia
Aug. 17, 2017 (MedicalXpress) -- Women who live in areas with higher levels of outdoor light at night may be at higher risk for breast cancer than those living in areas with lower levels, according to a large long-term study from Harvard T.H. Chan School of Public Health. The link was stronger among women who worked night shifts.
The study will be published online Aug. 17, 2017, in Environmental Health Perspectives.
"In our modern industrialized society, artificial lighting is nearly ubiquitous. Our results suggest that this widespread exposure to outdoor lights during nighttime hours could represent a novel risk factor for breast cancer," said lead author Peter James, assistant professor at Harvard Medical School's Department of Population Medicine at Harvard Pilgrim Health Care Institute, who did the work while a research fellow in the Departments of Epidemiology and Environmental Health at Harvard Chan School.
Previous studies have suggested that exposure to light at night may lead to decreased levels of the hormone melatonin, which can disrupt circadian rhythms -- our internal "clocks" that govern sleepiness and alertness -- and, in turn, lead to increased breast cancer risk.