Sun Avoidance and the Risk of Developing Breast Cancer: A Systematic Review and Meta-Analysis

摘要

Background: A relationship has been hypothesized between moderate solar ultraviolet radiation (UVR) exposure and breast cancer. This hypothesis centers on the antiproliferative and apoptotic properties of vitamin D, as well as increases in nocturnal melatonin concentrations which have been shown to slow cellular proliferation. To date, the literature on the effects of exposure to UVR and breast cancer risk have not been systematically reviewed and synthesized. Furthermore, the effects of sun avoidance (low amounts of time spent in the sun) in different exposure windows (adolescence vs. a period relevant to diagnosis) have not been compared. Methods: We conducted a systematic review and meta-analysis to investigate the association between sun avoidance (defined as less than an hour of sun per day) and the risk of developing breast cancer. Associations were estimated using random effects models. Heterogeneity was investigated through subgroup analyses and 12 statistics. Results: Seven studies were included in this review with the majority (n=5) being conducted in Canada or the US. We observed an increased risk of breast cancer for individuals obtaining less than an hour of sun exposure per day during summer months compared to individuals that obtained greater than an hour (pooled relative risk (RR) = 1.15; 95% CI: 1.09-1.20). Heterogeneity among this body of literature was minimal (12 = 2.7%) Among studies that measured sun exposure over different life periods, sun avoidance during adolescence appeared to confer a qualitatively greater risk of breast cancer than that closer to diagnosis (pooled RR = 1.18; 95% CI: 1.05-1.30 vs. 1.05; 95% CI: 0.88-1.25). Conclusion: This is the first meta-analysis to estimate the risk of developing breast cancer associated with sun avoidance. The results of this study suggest that obtaining less than one hour of sun per day during summer months, especially in adolescence, could increase the risk of developing breast cancer.