What Causes, Prevents Colon Polyps

Vitamin D Shines in New Study; Smoking Worse Than Expected

From the WebMD Archives

Dec. 9, 2003 -- In about five minutes each morning, you may be able to effortlessly and substantially reduce your risk of the nation's second most deadly cancer: Just take an aspirin, a multivitamin, and eat a bowl of fiber-packed cereal with some milk. If you want even more protection, add a 10-minute walk on sunny days without wearing sunscreen.

So suggest the results of the one of the largest and most comprehensive studies to date on factors that raise and lower the risk of colon cancer. In this new report, vitamin D shines -- it's associated with a one-third reduced risk of serious colon polyps that often lead to cancer in men getting at least 645 IUs of this nutrient each day.

"That's what you'll find in a multivitamin supplement and a small glass of milk," says lead investigator David A. Lieberman, MD, chief of gastroenterology at the Portland VA Medical Center. "Other vitamins also seem to have a protective effect, but our study suggests a stronger protective effect from vitamin D."

That's because vitamin D keeps cells from over-proliferating and multiplying too quickly. "Cells in the lining of the colon are constantly turning over and reproducing," Lieberman tells WebMD. "A drug that could prevent that, theoretically, could prevent cell mutations that can lead to cancer."

A similar protective effect -- about one-third reduced risk of these polyps -- was noted in men who took a daily aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen. Just over 4 grams of cereal fiber a day, which is less than one-quarter ounce, also offered the same degree of protection. -->

The Value of Vitamin D

Taking a multivitamin -- most of which contain 400 IUs of vitamin D -- was associated with reducing polyp risk by about 25%. These multivitamins also contain adequate amounts of calcium, folate, vitamin E, and selenium, which Lieberman also found to help lower polyp risk, "but not as much as vitamin D," he says. In order to get the full protective effect of vitamin D -- at 645 IU -- add a small glass of milk daily to the multivitamin.

That doesn't surprise Michael Holick, MD, PhD, director of the Vitamin D Research Lab at Boston University Medical Center and considered by many to be the nation's leading authority on vitamin D. He was not involved in Lieberman's research, which is published in this week's Journal of the American Medical Association.

"In 1941, the very first edition of the medical journal Cancer Research included a study showing that people who lived in New Hampshire, Massachusetts, Vermont, and other higher-latitude states had a higher risk of dying from all types of cancer than people in Alabama, the Carolinas, and other sunnier states," Holick tells WebMD.

"In the 1980s, there were other studies linking vitamin D specifically to colon cancer. It was shown that colon cancer was higher in people deficient in vitamin D and that by increasing vitamin D to healthy blood levels, colon cancer risk was reduced by 50%. We all recognize that vitamin D is critical for bone health, but we have not appreciated, although we have known for at least 20 years, is that we need adequate amounts to keep cell growth in check."

Lieberman's study was a detailed analysis of how various dietary, lifestyle, and genetic factors influenced the development of these colon polyps, which often lead to colorectal cancers that kill some 55,000 Americans each year. None of the 3,100 veterans enrolled -- almost all men -- had any signs of colon polyps or cancer when the three-year study began, but being between ages 50 and 75, they were at a statistically higher risk of colon cancer.

They participated in the study at 13 VA centers across the U.S., but their levels of sun exposure were not measured. Most of the body's vitamin D comes from sunlight on bare skin, and getting about 10 minutes a day of sunscreen-free sun exposure when weather permits can absorb some 20,000 IUs of vitamin D, says Holick.

"This can be stored in fat layers," he says. But during winter months, he recommends taking a daily multivitamin, along with a separate 400 IU vitamin D supplement to lower risk of colon and other cancers.

Avoid Smoking, Red Meat

As expected, Lieberman's study also confirms previous research that being overweight, alcohol consumption, or frequently consuming fatty meats can boost risk. Men having beef, pork, or lamb more than four times a week were nearly three times as likely to develop polyps.

But the big surprise was in the risk caused by smoking. Being a current smoker doubled the risk of these polyps -- more than having a parent or sibling with colon cancer, which upped risk by 70%. Lieberman's theory: Smoking stimulates the overgrowth of cells in the lining of the colon, as it's been shown to do in other organs.

"In past studies, smoking was found to have a smaller or marginal effect, but we found it was profound -- never before was the risk higher than a high-degree relative with colon cancer," Lieberman tells WebMD. "This provides yet another reason to not smoke."

Show Sources

SOURCES: Lieberman, D. TheJournal of the American Medical Association, Dec. 10, 2003; vol 290: pp 2959-2967. David A. Lieberman, MD, chief of gastroenterology, Portland VA Medical Center; chief of gastroenterology and professor of medicine, Oregon Health and Science University, Portland. Michael Holick, MD, PhD, director, The Vitamin D Research Lab; director, The General Clinical Research Center; professor of medicine, dermatology, physiology, and biophysics, Boston University Medical Center, Boston.
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