Vitamin D and Cancer: Diversity, Complexity, and Still a Ways to Go.

Vitamin D has taken a center-stage role in our basic and population research quest for the panacea for all human maladies, including cancer, yet sufficient evidence for a beneficial role has existed only for bone health. This Commentary discusses and places into a broader context the report of Chandler and colleagues that found a protective association for higher vitamin D status in colorectal cancer in women, consistent with most other cohort studies but not with limited supplementation trial data. Little human evidence exists for the preventive potential in other malignancies, including breast cancer, with the exception of possible benefit in bladder cancer and an adverse serologic association with prostate cancer (pancreatic cancer risk may be similarly influenced) that is supported by vitamin D genetic data. Current vitamin D trials are examining high-dose supplementation (i.e., 1,600-3,333 IU daily) for effects on multiple outcomes, but they may not have sufficient power to test efficacy in colorectal or other specific malignancies and are unlikely to inform any benefit for higher physiologic levels. A more complete understanding of vitamin D and human carcinogenesis will come from multifaceted lines of research, including elucidation of organ site-specific biologic mechanisms, prospective serologic analyses, testing of vitamin D-related genetic variation, and short-term clinical-metabolic biomarker studies of multidose vitamin D supplementation, including metabolomic profiling of controlled supplementation in these and past or ongoing trials.