Women who live in areas with higher levels of outdoor light at night may be at

higher risk for breast cancer， according to a study from Harvard T.H. Chan

School Of Public Health. The link was stronger among women who worked night

shifts.

Previous studies have suggested that exposure to light at night may lead to

decreased levels of the homone melatonin ， which can disrupt circadian

rhythms—our internal ’clocks’ that govern sleepiness and alertness—and， in turn，

lead to increased breast cancer risk.

The new study， the most comprehensive to date to examine possible links between

outdoor light at night and breast cancer， looked at data from nearly 110，000

women enrolled in the Nurses’ Health Study II from 1989-2013. The researchers

linked data from satellite images of Earth taken at night time to residential