“Calcium is pretty clearly a beneficial factor for lowering the risk of colorectal cancer,” says Walter Willett, chair of the nutrition department at the Harvard T.H. Chan School of Public Health. “The overall data strongly suggests that calcium protects the colon,” he explains.
When researchers pooled data from 10 studies on more than 534,000 people, for example, those who consumed about 1,000 milligrams of calcium a day had roughly a 20 percent lower risk of colorectal cancer than those who consumed less than 500 mg a day.
Dairy products also may lower the risk, likely through the calcium they contain, adds Willett.
Calcium may bind—and neutralize—bile acids released from the gallbladder that might be toxic to the colon’s lining.
Another possible reason: calcium may neutralize the carcinogens called nitrosamines that are created both outside and inside the body.
Nitrites to nitrosamines
Outside the body, nitrosamines form in processed meats when they’re cured using sodium nitrite. But since 1978, the U.S. Department of Agriculture has required bacon to contain either vitamin C or its chemical cousin sodium erythorbate to inhibit the formation of nitrosamines. Many other types of processed meats with added nitrites have also added vitamin C or sodium erythorbate to do the same.
Nitrosamines can also form inside the body from the naturally occurring nitrates in water and vegetables.
The role of calcium
Calcium seems to suppress the formation of nitrosamines inside our GI tract. Giving people 1,000 mg of calcium as calcium carbonate, for instance, eliminated the increase in nitrosamines that they excreted when they were fed six ounces a day of cooked ham for four days.
What has befuddled scientists are the results of two large clinical trials that gave 1,200 mg of calcium a day to people who had already had a precancerous colon polyp removed. These are people who are more likely to develop another precancerous polyp. Both studies were led by John Baron, now professor of medicine at the University of North Carolina.
In the first trial, calcium cut the risk of precancerous colon polyps by 15 percent. In the second, calcium had no impact.
We don’t know why. “John Baron has spent many long nights trying to understand the ambiguous results,” says Willett.
Shoot for the Recommended Dietary Allowance for calcium. The RDA for adults is 1,000 mg a day. It jumps to 1,200 mg for women over 50 and men over 70. “Most of the benefit comes from getting 800 or 1,000 mg a day,” says Willett.
“You can basically get there with one or two servings of dairy foods on top of a healthy diet. Or you can take a calcium supplement. With their calories and saturated fat, some dairy foods are a very expensive way to get some calcium,” Willett advises.
“And avoid processed meat,” he adds. “Eat it no more than a couple of times a year, not just to lower your risk of colorectal cancer, but also diabetes and cardiovascular disease.”
- The best evidence shows that calcium supplements are not bad for your heart
- Too much calcium from supplements may increase your risk of dying from prostate cancer
- Is Calcium Citrate a Better Mineral Supplement than Calcium Carbonate?
- Can Calcium Lower the Risk of Colorectal Cancer from Eating Cured Meats?
- How much calcium and Vitamin D do you need?
Find this article about calcium and colorectal cancer interesting and useful? Nutrition Action Healthletter subscribers regularly get sound, timely information about staying healthy with diet and exercise, delicious recipes, and detailed analyses of the healthy and unhealthy foods in supermarkets and restaurants. If you’re not already subscribing to the world’s most popular nutrition newsletter, click here to join hundreds of thousands of fellow health-minded consumers.