Vitamin D and calcium fail colon cancer prevention test – USA TODAY
Despite high hopes that they might help prevent colon cancer, supplements of vitamin D and calcium failed to prevent pre-cancerous colon polyps in a new study.
The study, published Wednesday in the New England Journal of Medicine, is the latest to dampen scientific enthusiasm for supplements in general and vitamin D and calcium in particular. It comes just days after two studies found no bone-health benefits for older adults taking calcium supplements. And it builds on previous trials finding scant evidence that vitamin D prevents cancer, at least in the doses and time frames studied so far.
“Vitamin D has gotten a lot of popular press,” and many people take it in hopes of preventing all sorts of health problems, but “we got what we got and it’s negative,” said lead researcher John Baron, a professor of medicine at the University of North Carolina at Chapel Hill.
For the new study, Baron and colleagues recruited 2,259 people ages 45 to 75 who had undergone removal of at least one adenoma, a colon polyp that can become cancerous if not removed. Participants took daily pills containing 1,000 IU (international units) of vitamin D, 1,200 milligrams of calcium, both or neither, and then underwent follow-up testing by colonoscopy after three to five years.
Result: 43% developed more adenomas and there were no significant differences among the various groups.
It’s possible that higher doses of vitamin D or a longer trial might yield different results, Baron said. He also said he and his colleagues were surprised to find no benefit from calcium because their previous trials strongly suggested one. The new trial found “just a hint” of a calcium benefit in lean participants, he says.
But, he said, the idea that vitamin D supplements might prevent colon cancer is based on weaker evidence, including observational studies that find lower rates in people with higher vitamin D blood levels. Such links might be due to healthy habits – including good diets and more active time outside, where the sun boosts vitamin D levels – rather than vitamin D per se, he said.
“There is mounting evidence that vitamin D does not prevent cancer,” said Barnett Kramer, director of the division of cancer prevention at the National Cancer Institute, which funded the new study.
But, Kramer said, more definitive evidence should come soon from a larger study led by researchers at Harvard University. That study is looking at cancer and heart disease and using vitamin D doses double those of the latest study – an important distinction because many vitamin D enthusiasts say higher doses may be needed.
For now, the Institute of Medicine recommends 600 IU of vitamin D daily up to age 70 and 800 IU after age 71. It says up to 4,000 IU daily is safe for adults. Food sources include fortified milk and juice. Recommended calcium intakes range from 700 mg. to 1,300 mg, depending on age and gender; 2,000 mg. is the safe limit for adults.. Sources include dairy foods and leafy greens.
The new study does not eliminate the possibility that vitamin D might prevent later stages of colon cancer development, said Marji McCullough, an expert in nutrition research at the American Cancer Society, Atlanta.
But there are established ways to prevent the disease, she said in an email. Those, she said, include eating a diet rich in fruits, vegetables and whole grains and low in red and processed meat, being physically active, not smoking, maintaining a healthy weight and following screening guidelines.