Light at Night and Risk of Breast Cancer

Principal Investigator:
Peggy Reynolds, Ph.D. (Principal Investigator), David Nelson, Ph.D.
Funding Source:
California Breast Cancer Research Program
Funding Period:
Study Website:
While women living in industrialized areas are well-known to be more likely to get breast cancer than their rural-dwelling counterparts, reasons for the urban excess of breast cancer remain enigmatic.  One provocative hypothesis is that increased exposure to night-time lighting associated with industrialization results in circadian disruption that could increase the risk of breast cancer through a variety of potential mechanisms. While there is convincing laboratory evidence that circadian disruption mediated by light-at-night exposures promotes mammary tumors in rodents, the degree to which light-at-night plays a role in the development of breast cancer in humans is not known.  This proposal capitalizes on newly-available satellite data on night-time illumination, on a well-developed urinary biomarker of melatonin (the primary hormonal modulator of circadian rhythms in mammals), and on existing survey data on indoor indicators of light-at-night exposures, to evaluate and develop methods to explore the relationship between these exposures and breast cancer risk among members of the California Teachers Study, a large, geographically diverse cohort of women for whom extensive information on known breast cancer risk factors is available.

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