RSSLight at night increases breast cancer risk

Posted on Tue, 28 Oct 14

Light at night increases breast cancer risk

A new study suggests that ambient light at night in urban environments may increase risk of breast cancer in women; disruption of your natural body clock may be to blame.

It has previously been found that women who work shifts have an increased breast cancer risk because of disruption of their body clock, and a new study suggests that ambient light at night in urban environments may increase risk even in women who have daytime jobs.  

A large study of some 106,731 Californian teachers looked at correlations between lighting while sleeping and subsequent development of breast cancer. Over the 15-year study period 5095 cases of invasive breast cancer were diagnosed with an increased risk in women living in areas with the highest level of outdoor light-at-night exposure, even after accounting for other breast cancer risk factors.

“In summary, our study provides evidence that women who live in areas with high levels of ambient light at night are at an increased risk of breast cancer not readily explained by other neighborhood characteristics or personal breast cancer risk factors” concluded the investigators.

“These results, found in a well-specified cohort of women who do not typically work at night, add another important line of evidence to the circadian disruption hypothesis beyond the well-documented increased breast cancer risk among night shift workers, suggesting that light at night may be a contributing etiologic factor.”


Hurley S, Goldberg D, Nelson D, Hertz A, Horn-Ross PL, Bernstein L, Reynolds P. Light at night and breast cancer risk among California teachers. Epidemiology. 2014 Sep;25(5):697-706.

Tags: Light At Night, Breast Cancer, Melatonin

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