Background: Epidemiologic evidence suggests a negative relation between sunlight exposure and breast cancer risk. The hypothesized mechanism is sunlight-induced cutaneous synthesis of vitamin D.
Objectives: Our goal was to examine sun exposure and its interaction with vitamin D receptor (VDR) gene variants on breast cancer risk.
Methods: We examined sun exposure and breast cancer incidence among 31,021 private pesticide applicators鈥?wives, including 578 cases, enrolled in the prospective Agricultural Health Study cohort and followed 8.6 years on average. We estimated interactions between sun exposure, VDR variants, and breast cancer in a nested case鈥揷ontrol study comprising 293 cases and 586 matched controls. Information on sun exposure was obtained by questionnaire at cohort enrollment. Relative risks were estimated using Cox proportional hazards regression for the cohort data and conditional logistic regression for the nested case鈥揷ontrol data.
Results: We observed a small decrease in breast cancer risk in association with usual sun exposure of 鈮?1 hr/day (versus < 1 hr/day) 10 years before the start of follow-up among all participants [hazard ratio (HR) = 0.8; 95% CI: 0.6, 1.0]. The association appeared to be slightly stronger in relation to estrogen receptor鈥損ositive tumors (HR = 0.7; 95% CI: 0.5, 0.9) than estrogen receptor鈥搉egative tumors (HR = 1.1; 95% CI: 0.6, 2.1). The HR for joint exposure 鈮?1 hr/day of sunlight and one VDR haplotype was less than expected given negative HRs for each individual exposure (interaction p-value = 0.07).
Conclusion: Our results suggest that sun exposure may be associated with reduced risk of breast cancer, but we did not find clear evidence of modification by VDR variants. Larger studies are warranted, particularly among populations in whom low levels of usual sun exposure can be more precisely characterized.
1Department of Epidemiology, University of North Carolina Gillings School of Global Public Health, Chapel Hill, North Carolina, USA; 2Department of Epidemiology and Biostatistics, Memorial Sloan-Kettering Cancer Center, New York, New York, USA; 3Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, USA; 4National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, North Carolina, USA
Recommended Citation:
Lawrence S. Engel,1 Jaya Satagopan,2 Camelia S. Sima,et al. Sun Exposure, Vitamin D Receptor Genetic Variants, and Risk of Breast Cancer in the Agricultural Health Study[J]. Environmental Health Perspectives,2014-01-01,Volume 122(Issue 2):165