A new study published in Environmental Health Perspectives concluded that women who live in areas with higher levels of outdoor lights at night may be at a greater risk of breast cancer than women in areas of lower light, The link was stronger among women who worked nights Previous studies have found that exposure to light at night may lead to decreased levels of the hormone melatonin that can effect our circadian rhythms and lead to breast cancer.
In the study nearly 110,000 women enrolled in the Nurses Health Study II between 1989 and 2013 were evaluated. Data on night satellite images of earth residential addresses were linked to for each participant and also considered night work or not. Data on health and socioeconomic factors were also considered. Women exposed to the upper level of light at night (the top fifth) had an estimated 14% increase in breast cancer during the study period than those in the lowest fifth. As the light increased outside so did the risk of breast cancer.
This relationship was found only among women who were premenopausal and those who were current or past smokers. In addition, the link was stronger among women who worked nights. The researchers said further research is needed.