The latest study on whether vitamin D can prevent cancer is negative, but there have been many such trials, and the findings have been contradictory. The latest results come from New Zealand are based on a post hoc analysis of the Vitamin D Assessment (ViDA) study.

The latest study on whether vitamin D can prevent cancer is negative, but there have been many such trials, and the findings have been contradictory. The primary purpose of the ViDA study was to investigate cardiovascular outcomes.

It found that taking high doses of vitamin D for up to 4 years without calcium was not associated with reductions in cancer incidence or cancer mortality. The cumulative incidence of cancer during a median follow-up of 3.3 years was 6.5% for those who received 100,000 IU of vitamin D3 each month.

By comparison, the cumulative incidence of cancer during the same period was 6.4% among participants who received placebo (adjusted hazard ratio [HR], 1.01; P = .95).

"Monthly high-dose vitamin D supplementation may not be associated with cancer prevention and should not be used for this purpose," said Robert Scragg, MBBS, of the University of Auckland, and colleagues.

Scragg and colleagues note that other randomized clinical trials of vitamin D supplementation have provided inconsistent results. They point out that these latest results on cancer incidence are consistent with findings from previous randomized clinical trials of community samples from the United States and the United Kingdom, and they are also consistent with the results from a recent meta-analysis of vitamin D supplementation trials.

Considerable Interest

Approached for comment, Carolyn Y. Fang, Ph.D., co-leader of Cancer Prevention and Control at Fox Chase Cancer Center in Philadelphia, Pennsylvania, said that in spite of the current study's null findings, "there is still considerable interest in the possible connection between vitamin D and cancer."

Clinicians should talk to patients who have vitamin D deficiency about how they can make healthy dietary or behavioral changes and whether taking a vitamin D supplement is warranted, said Fang.

"However," she added, "from a population health perspective, key questions regarding the appropriate 'dosage' of vitamin D for cancer prevention and how long one might need to take this dose to positively impact health remain to be addressed."

Conflicting Results

Results of previous studies on whether vitamin D can reduce cancer risk are conflicting. In the largest and most comprehensive observational study to date, an international research group concluded that vitamin D was unlikely to provide primary prevention of lung cancer, even in nonsmokers.