Sunlight Exposure and Breast Cancer Risk: A Systematic Review and Meta-analysis.

In 30 seconds

This systematic review and random-effects meta-analysis combined 31 epidemiologic studies to assess sunlight exposure and breast cancer incidence, subtype, and survival. Higher exposure was associated with lower overall incidence (pooled OR, 0.80; 95% CI, 0.74-0.86). Associations were strongest in case-control studies using personal exposure measures and weaker in cohorts using ambient ultraviolet proxies. Lower risk was observed for ER-negative and triple-negative tumors, but not ER-positive disease. Diagnoses in sunnier seasons were also associated with improved survival. The authors characterize the findings as hypothesis-generating given observational evidence and potential confounding and exposure misclassification.

Key findings

• Higher sunlight exposure was associated with lower breast cancer incidence (pooled OR, 0.80; 95% CI, 0.74-0.86).
• Associations were present for ER-negative tumors (OR, 0.71; 95% CI, 0.58-0.87) and triple-negative tumors (OR, 0.55; 95% CI, 0.37-0.81), but not ER-positive disease.
• Breast cancer diagnoses in sunnier seasons were associated with improved survival (hazard ratio, 0.84; 95% CI, 0.80-0.88).
• Dose-response analysis indicated an 8% lower risk per 10 relative exposure units.

Why it matters

The subtype-specific associations suggest that sunlight exposure may relate differently to breast cancer biology across receptor groups, while the survival finding raises a separate question about seasonal light exposure. These results may help guide research into environmental influences on breast cancer, but they do not establish that sunlight itself reduces risk; any consideration of exposure must also account for skin cancer risk.

What to keep in mind

The evidence is observational and subject to confounding and exposure misclassification; exposure measures also differed across study designs.