Calcium + Vitamin D = Lower Cancer Risk
The Two Nutrients Act Together to Prevent Colorectal Polyps
Dec. 2, 2003 -- Studies show that dietary calcium helps protect against colorectal cancer, but it appears to need a little help from vitamin D.
The new research shows that calcium and vitamin D act synergistically to protect against cancer of the colon. Calcium supplementation did not have much of an effect on the development of precancerous polyps when serum vitamin D levels were low in a study that involved nearly 800 people. And higher vitamin D levels were associated with a reduced risk of colorectal polyps only in people taking calcium.
"These findings suggest that from a protection standpoint, calcium and vitamin D do act together," study co-author John A. Baron, MD, tells WebMD. "Taking calcium alone doesn't appear to do the trick."
Baron and colleagues had previously reported that calcium supplementation significantly reduced the risk of developing recurrent colorectal polyps in the largest placebo-controlled clinical trial of calcium and colorectal cancer prevention ever. Colorectal cancer is one of the main causes of cancer deaths in the U.S., and studies show that diets consumed by western populations have a role in causing this cancer. Calcium appears to have a role in the growth of normal colon cells. Most colorectal cancers develop from benign growths called polyps, known as adenomas, which later may develop into cancer.
In their latest report, the researchers assessed the impact of vitamin D levels on adenoma recurrence among 803 of the study participants. They found that calcium supplementation protected against new adenomas only in people with serum vitamin D levels above average levels -- in this study that was a level of 29.1ng/ml. Similarly, vitamin D levels were associated with a reduced risk for polyp recurrence only among people who were taking supplemental calcium.
The reduction in colorectal cancer risk in people who took calcium and had higher levels of vitamin D was similar to that seen in those who exercise regularly, Baron tells WebMD. The study is reported in the Dec. 3 issue of the Journal of the National Cancer Institute.