Abstract: Objectives: To explore the association of colorectal cancer with environmental solar radiation and sun exposure behavior, considering phenotypic variables (eye color, hair color and skin phenotype), dietary intake of vitamin D and calcium, and socio-demographic factors. Study design: Multicenter population-based frequency matched case-control study in Spain (MCC-Spain), with 2140 CRC cases and 3950 controls. Methods: Data were obtained through personal interviews using a structured epidemiological questionnaire that included socio-demographic data, residential history, environmental exposures, behavior, phenotypic and dietary information. An environmental-lifetime sun exposure score was constructed combining residential history and average daily solar radiation, direct and diffuse. Logistic regression was used to explore the association between different variables. A structural equation model was used to verify the associations of the conceptual model. Results: We found a lower risk of CRC in subjects frequently exposed to sunlight during the previous summer and skin burning due to sun exposure. No association was observed in relation to the residential solar radiation scores. Subjects with light eye or light hair colors had a lower risk of CRC that those with darker colors. Dietary calcium and vitamin D were also protective factors, but not in the multivariate model. The structural equation model analysis suggested that higher sun exposure was associated with a decreased risk of CRC, as well as dietary intake of calcium and vitamin D, and these factors are correlated among themselves and with environmental solar radiation and skin phenotypes. Conclusion: The results agree with previous observations that sun exposure, dietary vitamin D and calcium intake, and serum 25(OH)D concentration reduce the risk of CRC and indicate that these factors may be relevant for cancer prevention.

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