Calcium May Reduce Colon Cancer Risk
Calcium seems to protect high-risk people from developing the polyps that can lead to colorectal cancer -- and the benefits appear to last long after calcium supplementation ends.
WebMD News Archive
Jan. 16, 2007 -- Calcium seems to protect high-risk people from developing
the polyps that can lead to colorectal
cancer -- and the benefits appear to last long after calcium
Patients with a history of nonmalignant polyps took either 1,200 milligrams
of calcium in supplement form or a placebo daily for four years in a study
previously reported by researchers from Dartmouth Medical School. Calcium use
was associated with a 17% lower relative risk for polyp recurrence.
This risk reduction not only persisted in the years after treatment ended,
but it seemed to strengthen, the Dartmouth researchers report in a newly
published follow-up that included 822 of the 930 original study subjects.
During the first five years after the end of treatment, 31.5% of patients in
the calcium group developed new polyps, compared with 43.2% of the study
participants who did not take calcium. The protection did not appear to extend
beyond five years, however.
The findings are published in the Jan. 17 issue of the Journal of the
National Cancer Institute.
"It really does look like calcium interferes with carcinogenesis [cancer
development] in the large bowel," researcher John A. Baron, MD, tells
WebMD. "The fact that this reduction in risk persisted for years after
people stopped taking calcium is really amazing."
Polyps are growths in the colorectal area. Some polyps can become cancerous
But Baron says it is still not clear if the benefits of taking calcium
supplements outweigh the risks among men because some studies have linked the
treatment to an increase in prostate cancer
The American Cancer Society recommends that adults aged 19 to 50 take in
1,000 milligrams per day of calcium and that those over 50 get 1,200
milligrams. But the guidelines stress that the calcium should come primarily
from food sources and not supplements.
guidelines, which were updated in 2006, also state that because of the possible
increased risk of prostate cancer
with high calcium intake, "it may be wise for men to limit their daily
calcium intake to less than 1,500 milligrams per day until further studies are
University of Arizona epidemiology professor Maria Elena Martinez, PhD,
worries that the findings from the Dartmouth follow-up study will drown out
"Americans tend to think that if some is good then more is better,"
she tells WebMD. "But for men at least, we have to keep in mind that more
isn’t better in this case and that taking calcium supplements in high doses may
even be dangerous."
Colonoscopy Best Risk Reducer
Another concern, Martinez says, is that people will get the idea that all
they need to do to prevent colorectal
cancer is take calcium supplements or eat calcium-rich foods.
Though the Dartmouth findings show calcium to be modestly protective against
colorectal cancer, another major study published in 2006 failed to show a
Calcium and vitamin D supplements proved to be somewhat protective for bone
density in the Women’s Health Initiative (WHI) trial. But no
difference in colorectal cancer risk was seen for an average of seven years of
follow-up among women who took calcium and vitamin D and those who did not.
In an editorial accompanying the Dartmouth study, Martinez points out that
despite the fact that polyp removal through screening is a highly effective way
to prevent colorectal cancer, most people either aren’t getting the message or
are ignoring it.
"If you want to prevent colon cancer, the best thing you can do is get a
colonoscopy when you turn 50 and make sure that you have follow-up
colonoscopies as needed," she tells WebMD. "That isn’t as easy as
popping a pill, but it is true."