Outdoor light at night and postmenopausal breast cancer risk in the NIH‐AARP diet and health study

• Published in: International journal of cancer 2020-11, Vol.147 (9), p.2363-2372
• Main Authors: Xiao, Qian, James, Peter, Breheny, Patrick, Jia, Peng, Park, Yikyung, Zhang, Dong, Fisher, Jared A., Ward, Mary H., Jones, Rena R.
• Format: Article
• Language: English
• Subjects: Aged; Breast - pathology; Breast cancer; Breast Neoplasms - epidemiology; Breast Neoplasms - pathology; Cancer; Carcinogenesis; circadian disruption; Circadian Rhythm - physiology; Circadian rhythms; Diet; Drinking behavior; Estrogen receptors; Female; Humans; Incidence; Light - adverse effects; Mastectomy; Medical research; Middle Aged; outdoor light at night; Photoperiod; Post-menopause; postmenopausal breast cancer; Postmenopause - physiology; prospective cohort; Receptors, Estrogen - metabolism; Residence Characteristics - statistics & numerical data; Risk Factors; Sleep; Sleep - physiology; Subpopulations; Time Factors; United States - epidemiology
• ISSN: 0020-7136; 1097-0215
• DOI: 10.1002/ijc.33016

Circadian disruption may play a role in breast carcinogenesis. Previous studies reported relationships between outdoor light at night (LAN) and the breast cancer risk, but their findings are mixed. There is also a need to examine LAN and breast cancer incidence according to different individual and environmental characteristics to identify subpopulations at greater risk associated with LAN exposure. We studied residential outdoor LAN estimated from satellite imagery at baseline (1996) in relation to postmenopausal breast cancer incidence over ~16 years of follow‐up in 186 981 postmenopausal women including 12 318 incident postmenopausal breast cancer cases in the NIH‐AARP Diet and Health Study. We used Cox proportional hazards models to estimate hazard ratios (HR) and two‐sided 95% confidence intervals (CI) of the relationship between quintiles of LAN and postmenopausal breast cancer risk, overall and by hormone receptor status and cancer stage. We found that when compared to women in the lowest quintile of baseline LAN, those in the highest quintile had a 10% increase in postmenopausal breast cancer risk (HR (95% CI), 1.10 (1.02, 1.18), P‐trend, .002). The association appeared to be stronger for estrogen receptor (ER) positive breast cancer (1.12 [1.02, 1.24], .007) than for ER‐negative cancer (1.07 [0.85, 1.34], .66). Our findings also suggested that the relationship between LAN and breast cancer risk may differ by individual characteristics, such as smoking, alcohol drinking, sleep duration and BMI, and neighborhood environment. In conclusion, our study suggests that higher outdoor LAN exposure may be a risk factor for postmenopausal breast cancer. What's new? Exposure to outdoor light at night (LAN) is associated with increased breast cancer risk, an affect attributed to LAN impacts on nocturnal melatonin production and circadian regulation. However, associations between LAN and breast cancer risk vary markedly, depending on different factors. Here, the impact of outdoor LAN exposure on breast cancer risk was investigated among postmenopausal women. High LAN levels were associated with increased postmenopausal breast cancer risk, with associations modified by neighborhood and lifestyle factors, including smoking and sleep duration. The findings highlight the importance of individual and environmental factors in modifying the relationship between LAN and breast cancer.