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Combo of two agents shows promise against colorectal cancer

It's long been known that vitamin D and calcium work both independently and in tandem to provide beneficial effects in the body. Vitamin D regulates the body's calcium levels by facilitating the small intestine's ability to absorb dietary calcium; by interacting with parathyroid hormone to enhance the mobilization of calcium from bone; and by decreasing the amount of calcium excreted by the kidneys. Now DMS researchers have found that vitamin D and calcium work together to reduce the risk of colorectal cancer, too.

Finding: The new finding actually came from a reanalysis of data gathered in a six-center study led by John Baron, M.D., a DMS professor of medicine and of community and family medicine. The study's initial finding was that calcium supplements can prevent colorectal polyps— benign tumors that can develop into colon cancer over time. For the new paper, lead author Maria Grau, M.D., M.P.H., with Baron and others, looked at whether vitamin D appeared to have anything to do with the action of the calcium supplements.

The study was a randomized, double-blind, placebo-controlled trial of calcium carbonate as a chemopreventive agent for the recurrence of large-bowel adenomas, or polyps. To be eligible, subjects had to have had at least one microscopically confirmed tumor removed within three months of when the study started. Subjects also had to be endoscopically judged "clean" of remaining polyps; they were reexamined endoscopically one year and four years later. More than 800 people participated in the study.

The results of the new analysis, reported in the Journal of the National Cancer Institute, indicate that calcium and vitamin D work together to reduce the risk of colorectal adenoma recurrence. Calcium supplements prevented adenomas only among individuals with serum vitamin D levels that were higher than the average for the group.

Doses: It's not clear yet exactly how vitamin D and calcium interact, but the mechanism will certainly be the subject of many investigations to come. There are also questions about how best to exploit this new information. For example, what are the optimal doses of the two agents, and in what form are they maximally beneficial? Milk comes to mind, because it is rich in calcium and has long been fortified with vitamin D.

But Baron questions the wisdom of tampering with foods. Among other problems, it's much easier to get a toxic overdose of fat-soluble vitamins like vitamin D, than of water-soluble vitamins.

"No one ever said that it was going to be easy," Baron says of the work that still lies ahead.

Roger P. Smith, Ph.D.

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