Vitamin D and Cancer

Epidemiological studies, mostly ecological but also case-control and prospective studies show a negative association between residential sun exposure and incidence (or fatality) of major cancers: colon, breast, and prostate cancer, and non-Hodgkin lymphoma. And it has been suggested that this reduction in risk could be influenced by vitamin D synthesized in the skin as a result of sun exposure. Low serum vitamin D levels are linked to an increase in risk of colon cancer, and to a lesser extent to risk of breast cancer, but not to risk of prostate cancer or non-Hodgkin lymphoma. Intervention trials consisting in daily supplementation in vitamin D for several years have all failed to demonstrate an effect on cancer incidence. Hence, it is not clear whether the reduction in cancer risk associated with sun exposure is mediated by vitamin D or by another factor influenced by sun exposure such as inflammation or immunosuppression, or whether a low vitamin D status is simply a consequence of ill health