Vitamin D and cancer: an overview on epidemiological studies.

In recent years, a rapidly increasing number of studies have investigated the relationship of vitamin D with total cancer and site-specific cancer obtaining diverse findings. In this chapter we provide an overview of epidemiological studies of vitamin D intake, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D serum levels and vitamin D associated polymorphisms in relation to total and site-specific cancer risk. Overall, epidemiological evidence for total cancer is inconclusive. However, a large number of studies support a relationship of vitamin D with colorectal cancer and to a lesser extent with breast cancer. Findings are inconsistent for other cancers including all other gastrointestinal cancers and prostate cancer. Different vitamin D associated polymorphisms were found to be significantly associated to colorectal, breast and prostate cancer risk.