Friday June 13, 2014 (foodconsumer.org) -- Early observational studies have suggested that taking vitamin D supplements may reduce the risk of cancer mortality, but not the risk of cancer development.  A meta-analysis of previous randomized controlled trials confirms the early conclusion.  During a period of 2 to 7 years, based on data from four trials, vitamin D supplementation was found to have little effect on total cancer incidence when the vitamin was used in a dose of 400 to 1100 per day.  However, based on data from three trials, vitamin D supplementation lowered the risk of death from cancer by 12%, which was significant.  Vitamin D experts may agree that the dosage used in the trials may be way too low.  For adults to have a preventative effect, a minimum of 5000 IU per day of vitamin D may be needed.

Keum N, Giovannucci E.  Vitamin D supplements and cancer incidence and mortality: a meta-analysis.  British Journal of Cancer 2014 Jun 10. doi: 10.1038/bjc.2014.294.