A major study found that supplementing with vitamin D and calcium neither successfully removed polyps – pre-cancerous colorectal adenomas – nor reduced risks for future colon cancers.
Research from the team at the University of Colorado Cancer Center, published Oct. 15 in the journal New England Journal of Medicine, offered strong evidence against these dietary supplements in preventing polyps in the future, despite optimistic results from previous, smaller trials.
“This was particularly surprising,” said study co-author and gastroenterology professor Dr. Dennis J. Ahnen, citing one of their previous trials that showed taking calcium supplements “could modestly reduce the risk of new polyp formation.”
The study involved 2,259 persons ages 45 to 75 and was conducted at 11 academic medical centers. Participants had colonic polyp removal, took daily vitamin D and/or calcium supplements, and underwent follow-up colonoscopy three to five years after initial testing.
Additional polyps showed in 43 percent of patients during second screening. In the next five years, there was also no significant difference in the occurrence of new polyps between those who supplemented and the control-group patients.
“Unfortunately, this trial shows that taking vitamin D or calcium is probably not very useful in this setting," Ahnen said.
Laboratory findings show that vitamin D slowed cancer cell growth through the inhibition of new blood vessels required to feed the malignant cells, as well as through apoptosis or cancer cell death. The tests on mouse models also yielded positive results.
The same is shown with calcium supplements, where people with higher calcium intake previously showed lower incidence of colorectal cancer. Smaller human trials, too, showed the mineral’s promise in preventing the disease.
Ahnen argued that “what works in a dish” and even in animal models does not consistently work in human trials.
The researchers added that while vitamin D and calcium can work later work in preventing lethal cancers, they hardly work on the “precancerous predecessors.”
Barnett Kramer, cancer prevention division director at the National Cancer Institute, said that “more definitive evidence” should be obtained soon from a larger, Harvard-led study that is looking at cancer and heart disease, and using vitamin D doses double of those in the NEJM study.
The Institute of Medicine currently recommends 600 international units of vitamin D every day for adults, and 800 IU for those older than 71. It sets 4,000 IU as the safe limit for adults. Calcium, on the other hand, is recommended to be taken from 700 to 1,300 milligrams daily based on age and gender, with 2,000 mg as the safe limit.
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