Neighborhoods with more light have higher breast cancer risk, study says

Story highlights

  • Study found direct relationship between neighborhood nighttime light level and woman's risk of breast cancer
  • Too much evening light can delay the normal transition to nighttime physiology

A new study from Harvard has found greater risk of breast cancer in women who live in neighborhoods that have higher levels of outdoor light during the night.

The findings are based on the Nurses' Health Study (NHS), which has for decades been advancing our understanding of risks to women's health.
For this study, epidemiologist Peter James and colleagues followed nurses in the NHS for breast cancer occurrence from 1989 to 2013. The home of each of 109,672 nurses was geocoded, and the average light level in the immediate neighborhood at night was estimated from satellite images taken by the Defense Meteorological Satellite Program.
    These estimates were updated over the 15-year follow-up period. By 2013, a total of 3,549 new cases of breast cancer had been diagnosed, about what's expected among this number of women.