CHICAGO – A study in nearly half a million older men and women bolsters evidence that diets rich in calcium may help protect against some cancers.
The benefits were mostly associated with foods high in calcium, rather than calcium tablets.
Previous studies have produced conflicting results. The new research involved food questionnaires from participants and a follow-up check of records for cancer cases during the subsequent seven years. This research method is less rigorous than some previous but smaller studies.
But because of its huge size — 492,810 people and more than 50,000 cancers — the new study presents powerful evidence favoring the idea that calcium may somehow keep cells from becoming cancerous, said University of North Carolina nutrition expert John Anderson, who was not involved in the study.
The study was run jointly by the National Institutes of Health and AARP. The results appear in Monday's Archives of Internal Medicine.
National Cancer Institute researcher Yikyung Park, the study's lead author, called the results strong but said more studies are needed to confirm the findings.
Duke University nutrition researcher Denise Snyder said the results support the idea that food rather than supplements is the best source for nutrients.
Participants were AARP members aged 50 to 71 who began the study in the mid-1990s. A total of 36,965 men and 16,605 women were later diagnosed with cancer. There were more than 10 different kinds of cancer, the most common being prostate, breast, lung and colorectal.
Compared with people who got little calcium, those who consumed the most had the lowest chances of getting colon cancer. Those in that highest category got on average 1,530 milligrams a day among men and 1,881 milligrams daily among women. The recommended amount for older people is 1,200 milligrams, and getting much more than that didn't result in any greater protection. Adults can get that amount from four cups of milk or calcium-fortified orange juice.
Men who got the most calcium from food were about 30 percent less likely to get cancer of the esophagus, about 20 percent less likely to get head and neck cancer and 16 percent less likely to get colon cancer, when compared to men who got low amounts of calcium.
Among women, those who got the most food-based calcium were 28 percent less likely to get colon cancer than low-calcium women.
In men, calcium supplements only seemed to help protect against colon cancer; for women, supplements meant a lower risk for liver cancer, which is rare.
Some previous studies have linked diets high in calcium with prostate cancer but the current study found no such risk.
Adults who ate the most calcium also tended to be healthier overall than the others.
Northwestern University preventive medicine instructor Patricia Sheean called the results impressive. But she noted that all those in the study, AARP members, may have been healthier and wealthier than the general U.S. population so it's not clear if the results would apply to the wider population.