Exposure to Artificial Light-At-Night and Obesity in a Population-Based Case-Control Study in Spain (MCC-Spain)

Abstract

Background. Exposure to light-at-night and circadian disruption may increase cancer risk. In experimental animals light-at-night is strongly associated with obesity. We evaluated the association of exposure to artificial light-at-night (ALAN) with obesity in a population based multicase-control study. We applied a novel method for exposure assessment examining visual light and blue light spectrum. We evaluated chronotype, a characteristic that may relate to adaptation to light-at-night. Methods. We examined 1825 subjects (1129 population controls, 696 breast and prostate cancer incident cases; 919 men, 906 women) from Barcelona and Madrid, enrolled in 2008-2013. Indoor-ALAN information was obtained through questionnaires. Outdoor-ALAN was analyzed using images for 2012-2013 from the International Space Station (ISS) including data of remotely sensed upward light intensity and blue light spectrum information for each subject’s geocoded longest residence. We examined excess-weight (BMI >=25); abdominal-obesity (waist-hip ratio >0.85 women, >0.90 men) and overall obesity (WHR as above and BMI>=30). ORs are adjusted for age, sex, education, center, case-control status and menopause (women).Results. Exposure to outdoor ALAN in blue light spectrum or visual light were not associated with measures of obesity (OR for highest tertile of blue light compared to lowest: 0.82 (95%CI 0.63,1.07) excess weight; OR=0.82 (0.60,1.13) abdominal obesity; OR=0.83 (0.61,1.13) overall obesity. ORs tended to be higher for subjects who slept in “quite illuminated” bedrooms compared to those sleeping in total darkness (excess weight OR=1.53 (0.98, 2.39); abdominal obesity OR=1.18 (0.68,2.03); total obesity OR= 1.36 (0.78,2.37). Results were similar when limited to controls and when mutually adjusting for indoor and outdoor light exposures. There was no effect modification by chronotype. Conclusion. Artificial light-at-night was not associated with excess weight or obesity.