UNC study finds higher vitamin D and calcium intake does not reduce colorectal polyp risk

October 14, 2015

A large, randomized study led by a researcher in the UNC Gillings School of Global Public Health found that vitamin D and calcium supplements do not reduce the risk of colorectal adenomas, which are benign tumors that can evolve into colorectal cancer.

The results, published Oct. 14 in the New England Journal of Medicine, came as a disappointment to the researchers. Previous observational studies had pointed to an association between lower colorectal cancer risk and higher vitamin D blood levels, and to lower colorectal cancer risk alongside increased calcium intake.

Dr. John Baron

“There’s a lot of interest in vitamin D these days because of many positive findings in non-randomized studies,” explained the study’s lead author John Baron, MD, research professor in the Gillings School and the UNC School of Medicine, and a member of the UNC Lineberger Comprehensive Cancer Center. “In particular, vitamin D has been investigated for its protective benefits against a range of diseases, including colorectal cancer.”

“We found that vitamin D and calcium supplements did not affect the occurrence of colon polyps, which are benign precursors to colorectal cancer. So our results came as a disappointment.”

Colorectal cancer is the fourth most common cancer in the United States, with an estimated 132,700 new cases and 49,700 deaths from the disease this year, according to NCI Surveillance, Epidemiology and End Results Program data. Colorectal cancers can develop from precancerous growths called adenomas.

The study included 2,259 people at 11 academic medical centers or affiliated medical practices. Patients recently diagnosed with precancerous adenomas, but who had no colorectal polyps remaining after a colonoscopy, were included.

Patients were randomly assigned to take either daily doses of 1,000 International Units of vitamin D₃, 1,200 milligrams of calcium, both or neither. Women could opt to receive calcium and be randomized to vitamin D or placebo.

The study found that 42.8 percent of patients developed one or more adenomas after taking the higher vitamin D doses, compared to 42.7 percent of patients who were not given vitamin D. Even after adjustment for variables such as age, gender and study center, there was essentially no difference between the two groups in the risk of adenomas.

Of patients taking the higher calcium doses, 45.3 percent developed adenomas compared to 47.6 of patients who did not take calcium. And 45.7 percent of patients taking both vitamin D and calcium developed one or more adenomas, compared to 48.2 percent taking neither. The relative risks were also not statistically significant for those comparisons.

While the study did not find that higher daily doses of calcium and vitamin D reduced the risk of recurrent colorectal adenomas across three to five years, Baron said the study paves the way for longer-term trials testing the effect of higher doses of vitamin D and calcium.

“Vitamin D did not reduce risk of adenomas, suggesting that it does not interfere with colorectal carcinogenesis, as thought,” Baron said of the study findings. “However, the data are consistent with a modest effect and there were suggestions that with longer treatment there might be some benefit.”

Robert S. Sandler, MD, Distinguished Professor of epidemiology at the Gillings School and chief of the UNC School of Medicine’s Division of Gastroenterology and Hepatology, as well as Anastasia Ivanova, PhD, associate professor of biostatistics at the Gillings School, also were co-authors of the study, which was supported by a grant from the National Institutes of Health’s National Cancer Institute.