Solar Ultraviolet Radiation and Breast Cancer Risk: A Systematic Review and Meta-Analysis

BACKGROUND: A protective relationship has been hypothesized between exposure to solar ultraviolet radiation (UVR) and the development of breast cancer. OBJECTIVE: The objective of this study was to conduct a systematic literature review and meta-analysis of studies examining the association of exposure to solar UVR and breast cancer risk. METHODS: We searched Medline, EMBASE, and Web of Science for all studies investigating exposure to solar UVR and breast cancer risk. Separate analyses were performed using estimates of time spent in the sun, and ambient UVR. Associations were estimated using DerSimonian and Laird random-effect models. Heterogeneity was investigated through subgroup analyses and [Formula: see text] statistics. RESULTS: Fourteen studies were included in the review and 13 in the meta-analysis, with the majority ([Formula: see text]) conducted in North America. We observed a decreased risk of breast cancer for individuals spending [Formula: see text] in the sun during summer months over a lifetime or usual adulthood compared with [Formula: see text] [[Formula: see text]; 95% CI: 0.77, 0.91]. Spending [Formula: see text] in the sun had a similar protective effect as 1 to [Formula: see text] when compared with [Formula: see text] ([Formula: see text] 0.83; 95% CI: 0.75, 0.93 vs. 0.83; 95% CI: 0.78, 0.89). Exposure during adolescence was suggestive of a lower risk of breast cancer than exposure later in life ([Formula: see text] of age) ([Formula: see text] 0.83; 95% CI: 0.71, 0.98 vs. 0.97; 95% CI: 0.85, 1.11). Ambient UVR was not associated with the risk of breast cancer ([Formula: see text] 1.00; 95% CI: 0.93, 1.09). DISCUSSION: To our knowledge, this was the first meta-analysis to estimate the risk of developing breast cancer associated with time spent in the sun. The results suggest that obtaining greater than an hour a day in the sun during the summer months could decrease the risk of developing breast cancer. https://doi.org/10.1289/EHP4861