Calcium’s benefit in lowering risk for colorectal cancer requires a higher-than-average vitamin D level, according to an article in the December 3rd issue of the Journal of the National Cancer Institute. The current work involved re-analysis of data from the Calcium Polyp Prevention Study (a 4-year, randomized trial with more than 800 participants), which documented a lower risk for adenomatous polyps in people who took calcium supplements.

The American investigators found that calcium supplements prevented adenomas only among individuals with baseline vitamin D levels that were higher than average (29.1 ng/mL). Similarly, serum vitamin D levels were associated with reduced adenoma recurrence only among individuals taking calcium supplements.

According to the authors, the findings "provide a strong indication that vitamin D and calcium have a joint antineoplastic effect in the large bowel," but are essentially ineffective without the other nutrient.

The authors added that "further investigation is needed to understand the mechanistic basis of the vitamin D/calcium interaction and to clarify the amount of intake of each nutrient required for optimum protective effect."