Got milk? Then drink to this: A new study has linked high calcium intake to lower incidence of cancers, including colon cancer, in men and women between the ages of 50 and 78.

In surveys of nearly 300,000 men and 200,000 women, researchers found that women who got about 1300 milligrams per day or more of calcium -- the equivalent of about four and a half cups of milk -- had a 7 percent lower risk of developing any type of cancer than those with the lowest intake -- about 500 milligrams per day, the equivalent of about one and a half cups of milk.

The researchers followed the study participants for seven years. When they looked at all gastrointestinal tract cancers together -- colon, pancreatic, stomach, esophageal and liver cancer -- women with the highest calcium intake (about 1,900 milligrams per day) had a 23 percent lower risk than those with the lowest intake (about 500 milligrams per day).

Among men, calcium had no significant effect on the overall cancer risk but did appear to influence digestive system cancers. Men with the highest intake (about 1500 milligrams per day) had a 16 percent lower risk than those with the lowest (about 500 milligrams per day).

Looking at each digestive cancer type individually (rather than clumping them together), they did not find statistically significant links to calcium, except in the case of colon cancer. Women getting the most calcium (about 1900 milligrams per day) were 28 percent less likely to develop colon cancer than those consuming the least (about 500 milligrams per day). Men with the highest calcium intakes (about 1500 milligrams per day) were 21 percent less likely to develop colon cancer than those consuming the least (about 500 milligrams per day).

(Just for some perspective, about 59.2 out of 100,000 men and 43.8 out of 100,000 women in the U.S. get colon cancer every year. Marji McCullough, a nutritional epidemiologist at the American Cancer Society, and Dana Flanders, an epidemiologist at Emory University's Rollins School of Public Health, said it would be cumbersome to calculate exactly how many cases of cancer might have been avoided by higher calcium levels based on the design of the study.)

More research is needed to confirm the results, cautions co-author Yikyung Park, an epidemiologist at the National Cancer Institute (NCI) in Bethesda, Maryland, even though the study, which is published today in the Archives of Internal Medicine, is the largest to link increased calcium intake to lower risk of cancers affecting the digestive system.

Calcium might ward off cancer by promoting the death of cells multiplying out of control, says the ACS’ McCullough. But vitamin D – a nutrient contained in many calcium-rich foods – appears to control cancer cell proliferation, and thus the cancer benefits illustrated in this study could be due calcium and vitamin D working together, she adds.

Calcium's apparent benefits might be dependent on vitamin D, agrees Jennifer Lin, an epidemiologist at Harvard Medical School. "It is possible that high intakes of both nutrients may be necessary for cancer prevention," she says. "In my previous study of breast cancer and calcium/vitamin D intake, we found that the relationship between calcium and breast cancer risk was modified by vitamin D intake -- lower breast cancer risk was associated with higher intakes of both calcium and vitamin D in older women."
For the average man and woman worried about getting cancer, this study doesn't suggest that going overboard with calcium will have much benefit. In fact, it could be dangerous, says McCullough, noting that some research suggests that men who take more than 2000 daily milligrams may be upping their risk of prostate cancer. "I would suggest going with recommendations from the Institute of Medicine [1200 milligrams per day for men and women ages 50 and above]," she says, "People would be wise to reach the recommended levels but not to think that more is better."