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Is Street Light Exposure a Risk Factor for Breast Cancer?

7/11/2017 12:54:34 PM
Thomas Edison patented the first commercial light bulb in 1879, forever changing the human experience of night. Light exposure serves as an environmental signal to biological clocks, with darkness stimulating the production of melatonin, which initiates physiologic changes in the cells, tissues, and organ systems. Outdoor and indoor lighting both contain short wavelength emissions that can disrupt melatonin production. The World Health Organization has declared shift work a probable carcinogen, and the American Medical Association established guidance in 2012 and 2016 to reduce the harmful effects of high intensity street lighting.
Researchers Keshet-Sitton and colleagues in Israel hypothesized that outdoor artificial light at night may disrupt melatonin production and therefore influence breast cancer morbidity. To test this hypothesis, they studied the association between outdoor light intensity and breast cancer morbidity in the Israeli city of Ashkelon.
The study involved 266 women with newly diagnosed breast cancer during the years of 2004 to 2012 in Ashkelon. The city was divided into statistical areas, and patients were matched to each area using zip codes. Street light measurements were conducted in each statistical area during 2015-2016 to serve as a proxy for light intensity exposures during the 10-15 years before breast cancer diagnosis. Standardized morbidity ratios (the number of observed breast cancer cases compared to the expected number of cases in the population) were calculated for each statistical area.
Breast cancer morbidity ratios per statistical area were significantly, positively, and strongly correlated with mean light intensity per road length, with 63% of the variation between statistical areas explained by mean light intensity (r=0.79; p<.01; R2=0.63). Approximately 16 lux at 140cm height was the threshold light intensity, above which statistical correlations were observed. The authors propose that this is the minimal intensity to suppress melatonin production and therefore increase breast cancer morbidity.
Although this study does not evaluate timing or duration of light exposure, the results show that the rate of breast cancer is higher among women living in areas with higher intensity of outdoor light. 
Reference: Mosca A, Nobili V, De Vito R, et al. Serum uric acid concentrations and fructose consumption are independently associated with NASH in children and adolescents. J Hepatol. 2017;66(5):1031-1036.