Light exposure at night, sleep duration, melatonin, and... : European Journal of Cancer Prevention (original) (raw)

Research Papers: Breast Cancer

a dose–response analysis of observational studies

Yang, Wan-Shuia,b,*; Deng, Qina,b,*; Fan, Wen-Yana,b; Wang, Wei-Yea,b; Wang, Xina,b

aJiangxi Province Key Laboratory of Systems Biomedicine

bDepartment of Social Science and Public Health, School of Basic Medical Science, Jiujiang University, Jiujiang, People’s Republic of China

* Wan-Shui Yang and Qin Deng contributed equally to the writing of this article.

All supplementary digital content is available directly from the corresponding author.

Correspondence to Xin Wang, MD, MSc, Jiangxi Province Key Laboratory of Systems Biomedicine, Jiujiang University, 551 East Qianjin Road, Jiujiang 332005, People’s Republic of China Tel: +86 792 857 7050; fax: +86 792 857 7050; e-mail: [email protected]

Received June 12, 2013

Accepted August 23, 2013

Abstract

Evidence from observational studies on light at night (LAN) exposure, sleep duration, endogenous melatonin levels, and risk for breast cancer in women is conflicting. This led us to conduct a dose–response analysis of published observational data. Pertinent studies were identified by searching Medline, Web of Science, and EMBASE through April 2013. The dose–response relationship between sleep duration, urinary 6-sulphatoxymelatonin levels, and breast cancer was assessed using the restricted cubic spline model and by multivariate random-effects metaregression. A separate meta-analysis was also carried out to calculate the relative risks (RRs) with 95% confidence intervals (CIs) for breast cancer for the comparable categories or highest levels of exposure versus the lowest levels. Twelve case–control and four cohort studies were included in the analysis. High artificial LAN exposure is associated with an increased risk for breast cancer (RR=1.17, 95% CI: 1.11–1.23), but not ambient LAN exposure (RR=0.91, 95% CI: 0.78–1.07). The summary RR for breast cancer is 1.00 (95% CI: 0.995–1.01) for an increment of 1 h of sleep per night. No significant dose–response relationship between sleep duration and breast cancer was found either for the linearity test (_P_trend=0.725) or for the nonlinearity (_P_trend=0.091) test. An increasein of 15 ng/mg creatinine in urinary 6-sulphatoxymelatonin is associated with a 14% reduced risk for breast cancer (RR=0.86, 95% CI: 0.78–0.95), with a linear dose–response trend (_P_trend=0.003). There was no evidence of substantial heterogeneity or publication bias in the analysis. Our study adds to the evidence of LAN breast cancer theory. Further research in this area is warranted.