In 2011, the Institute of Medicine (IOM) published a report that reviewed evidence linking serum levels of vitamin D with both skeletal and nonskeletal health outcomes in North America. The report showed strong evidence for an important role of vitamin D in bone health. However, evidence of an association between vitamin D levels and cancer or other outcomes beyond bone health was inconsistent.
There has been widespread enthusiasm for a role of vitamin D in preventing the development of cancer or slowing its progression, but there is little direct evidence linking vitamin D to cancer incidence or its prevention. Indirect evidence has shown an association between low serum 25-hydroxyvitamin D levels with confounding factors related to higher cancer risk, including obesity, lack of physical activity correlated with less sun exposure, dark skin pigmentation, and dietary or supplemental intake. Other indirect evidence from in vitro and in vivo model studies suggest that calcitriol promotes cell differentiation, and has anti-inflammatory, proapoptotic, and antiangiogenic actions, and also inhibits cancer cell proliferation.
The findings of several observational and other nonrandomized studies investigating the possible preventive role of dietary supplementation with vitamin D on risk of cancer or the possible association of low vitamin D serum levels with cancer have been inconsistent and conflicting. Specific cancers investigated have included breast cancer, colon cancer, prostate cancer, and less common cancers. Data from randomized clinical trials are sparse and provide little support for a preventive role of vitamin D in cancer or an association between low serum 25-hydroxyvitamin D levels and increased cancer incidence and mortality. In some randomized trials, high doses of vitamin D had harmful effects.
The conclusion of the report by the Institute of Medicine stated that existing data do not provide credible evidence for a role of vitamin D in preventing cancer is consistent with that of other recent reviews.