February 25, 2009
The New York Times

Calcium Linked to Lower Colon Cancer Risk, Study Finds

By RONI CARYN RABIN

A huge study of nearly half a million people found that older men and women who consumed large amounts of dairy foods and calcium were at reduced risk of developing digestive cancers, especially colorectal cancer. The findings have reignited a long-simmering debate over calcium’s potential to fight colon cancer.

Among women, high calcium intake was associated with a reduced overall cancer risk as well, the study found.

Previous studies have produced mixed results regarding the link between calcium and colon cancer.

The latest report, an observational study in which researchers reviewed dietary profiles for possible links to cancer, was published on Monday in The Archives of Internal Medicine. Such studies are not considered as reliable as randomized, controlled trials that compare a treatment in one group with a placebo in a similar group. “Our key finding is that higher total calcium intake is associated with a decreased risk of digestive system cancers,” said first author Dr. Yikyung Park, a cancer epidemiologist at the National Cancer Institute, who noted that current dietary recommendations to consume calcium are intended to promote bone health, not prevent cancer.

"Our study is just one study," she added. "We need to look to other studies to confirm the finding."

The study examined the relationship between dairy and calcium intake and cancers among 293,907 men and 198,903 women ages 50 to 71 who participated in the National Institutes of Health-AARP Diet and Health Study. Participants filled out a dietary questionnaire when they enrolled in the mid-1990s, noting how often they consumed dairy and other foods and whether they took supplements. Researchers then linked the participants’ records with state cancer registries to identify new cases of cancer diagnosed through 2003.

After seven years of follow-up, researchers found 36,965 cases of cancer in men and 16,605 cases in women. The researchers found that men who reported consuming the most calcium, about 1,500 milligrams daily, faced a 16 percent lower risk of developing cancers of the digestive system than those who consumed the lowest amounts, about 500 milligrams daily.

Women with the highest dairy and calcium intake had a 23 percent reduced risk of colon cancer, the scientists found, compared to women with the lowest intakes of calcium.

The scientists found no association between calcium intake and overall cancer risk in men, but found that women were at lower overall cancer risk if they reported high intakes of calcium, up to 1,300 milligrams daily. There were no added benefits with higher amounts.

Researchers had to make adjustments in their data to make sure there were no other factors affecting cancer rates, since those who consumed the highest amounts of calcium were more likely to be white, college-educated and physically active, and less likely to smoke and drink alcohol.

In 2006, a randomized controlled clinical trial that was part of the Women’s Health Initiative found no evidence to support the hypothesis that calcium prevents colon cancer.

But Dr. JoAnn Manson, one of the principal investigators of that trial and chief of preventive medicine at Brigham and Women’s Hospital in Boston, said the weight of the cumulative evidence suggests calcium does play a role in preventing colon cancer, noting that some studies have found calcium intake is associated with reduced occurrence of precancerous colon polyps.

The earlier trial may have not found any effect because the population studied was well nourished overall and many women in both groups had a high calcium and dairy intake, she said.

But she noted that vitamin D, which is often consumed with calcium, may be the pivotal player in cancer prevention and ought to be a focus of ongoing study.

"The totality of the evidence in aggregate is consistent with the benefit of dairy products and total calcium intake in the prevention of colorectal cancer,” she said. “But these studies really cannot disentangle the effects of calcium and vitamin D."

Experts noted that there is a plausible biological explanation as to how calcium may reduce colorectal cancer. Calcium may reduce the growth of abnormal cells in the gastrointestinal tract, Dr. Park said. Since calcium binds to bile and fatty acids, it may reduce damage to the mucous membranes of the large intestine, she said.

Dairy foods are also rich in other potentially anticarcinogenic nutrients, including vitamin D and conjugated linoleic acid.

The Institute of Medicine recommends that adults ages 50 and older consume 1,200 milligrams of calcium per day because it contributes to bone health.