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
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
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
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.
What Should You Do?
While the findings show that taking calcium and getting more
vitamin D can lower colorectal cancer risk, Baron says the message for the
public is not so clear-cut. Several studies show a link between dietary calcium
and an increased risk of prostate cancer, although the association was not seen
in this study. And while exposure to the sun is one of the best ways to get
vitamin D, this obviously carries its own risks.
"Right now it is difficult to know what to tell the public
about these findings because there are so many variables involved,"
researcher Elizabeth T. Jacobs, PhD, tells WebMD. "I know people get sick
of hearing this, but we need more studies before we can make specific
In addition to determining the levels of dietary calcium and
vitamin D needed to protect against colorectal cancer, Jacobs says future
studies should also examine the impact of genetic influences linked to the
In an editorial accompanying the study, Jacobs and colleagues
note that until these questions are answered, people may benefit most from
adopting lifestyle changes known to reduce the risk of colorectal cancer, such
as increasing physical activity, eating more fruits and vegetables, and eating
less red meat.