Scientists at the Harvard T.H. Chan School of Public Health have today suggested that women who live in areas with higher levels of outdoor light at night may be at a slightly increased risk of breast cancer than those living in areas with lower levels, following the publication of a new long-term prospective study.

Friday 18 August 2017      Latest research

The study, published today in Environmental Health Perspectives, analysed health and lifestyle data from nearly 110,000 female nurses, collected over almost 25 years. Combining this data with satellite images of Earth to determine night-time light levels, the researchers found that women living in areas with high levels of outdoor light at night may be at a slightly increased risk of breast cancer. When the researchers investigated whether this effect was restricted to specific groups of women, a significant link between outdoor light at night and breast cancer was only found among those who were premenopausal, or those who were current or previous smokers. The link was also stronger for women who worked night shifts, suggesting that exposure to light at night and night shift work contribute jointly to breast cancer risk.

Dr Richard Berks, Senior Research Communications Officer at Breast Cancer Now, said:

“That this study suggests a woman’s risk of breast cancer could be slightly affected if her neighbourhood is brighter at night is an interesting finding – but is one that requires further investigation.

“In particular, we hope further studies will investigate how the exposure to light at night and breast cancer risk is further impacted by smoking or menopausal status, to understand the possible biological mechanisms behind these risk factors.

“In the meantime, we’d encourage any women concerned about their breast cancer risk to consider known risk-reducing options, such as regular physical activity, maintaining a healthy weight, and cutting down on alcohol, before moving to the country or sleeping at the back of the house.”

To find out more about the steps you can take to reduce your risk of breast cancer take a look at our reducing your risk section.