The nutrients calcium and vitamin D work in tandem, not separately, to reduce the risk of colorectal cancer, according to a new Dartmouth study reported in the December 3 issue of Journal of the National Cancer Institute.
The research builds on a multi-center study led by Dartmouth Medical School professor John Baron that found that people who take calcium supplements have a lower risk of adenoma polyps -- benign tumors that are precursors to cancer of the colon or rectum. Now Baron, lead author Maria V. Grau of Dartmouth, and colleagues have re-analyzed that study to examine how calcium and vitamin D interact to lower the possibility of colorectal cancer.
More than 800 people participated in the Calcium Polyp Prevention Study, a four-year randomized trial that documented the benefits of calcium supplementation for preventing the growth of the benign tumors. The recent analysis 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.
These 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 the authors write. They add 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."
The vitamin D assays were all conducted at the UCLA Center for Human Nutrition.