Vitamin D may be more important to colon cancer prevention than previously believed, according to a study published in the Journal of the American Medical Association (Vol. 290, No. 22: 2959-2967).
The study examined people with no symptoms of colon cancer to determine what role diet, exercise, smoking, and other behaviors played in the development or not of colon polyps, small growths in the colon that can turn into cancer if they aren't removed.
"Higher levels of vitamin D were associated with a lower risk of serious colon polyps," said lead study researcher David Lieberman, MD, chief of gastroenterology at the Portland Veterans Affairs (VA) Medical Center and Oregon Health Sciences University. "There have been some studies suggesting this, but our data are compelling."
The role of vitamin D in colon cancer prevention is still a topic of debate, said Durado Brooks, MD, director of prostate and colorectal cancer for the American Cancer Society. Previous research has not been able to determine conclusively whether vitamin D alone is helpful, whether it must be consumed with calcium to have a protective effect, or whether calcium alone is really the important nutrient.
"Past studies have given more credence to calcium, and this suggests we need to look at vitamin D as potentially as important as calcium," Brooks said.
Vitamin D, Cereal Fiber, NSAIDs Protective
The new study, conducted at 13 VA medical centers, followed more than 3,000 people for 3 years. All the participants were between the ages of 50 and 75, and almost all of them (97%) were men. Everyone in the study had a colonoscopy to look for colon polyps, and the researchers compared people who had advanced (large) polyps with those who didn't.
The researchers asked the participants about many factors that could influence whether they developed colon polyps: smoking history, alcohol use, physical activity, family history of colon cancer, use of aspirin or other non-steroidal anti-inflammatory drugs (NSAIDs), diet, and weight.
Men who consumed more vitamin D in their diet each day were less likely to develop colon polyps, and men who consumed the most of the vitamin (more than 645 IUs, or international units) daily reduced their risk the most.
Vitamin D is found in fortified milk, salmon, cod liver oil, sardines, and mackerel. Spending time in the sun also helps the body produce vitamin D.
However, too much vitamin D can cause nausea, constipation, weakness, and other problems, so Lieberman cautioned against overdoing it.
According to the National Institutes of Health, people aged 19-50 need 200 IUs daily (in either their diet or in supplements) for adequate nutrition, while people between 51 and 69 should get 400 IUs each day. People 70 and older need 600 IUs of vitamin D each day. The Institute of Medicine's Food and Nutrition Board recommends an upper limit of 2,000 IUs of vitamin D for most children and adults, and no more than 1,000 IUs for babies under 12 months.
Cereal fiber was another important dietary factor for colon cancer prevention. People who ate more than 4 grams per day had a significantly lower risk of colon polyps. Exercise, calcium, and multivitamins also had a small benefit.
Taking NSAIDs had a significant protective effect. Men who took NSAIDs daily were only two-thirds as likely to get colon polyps as men who did not take the drugs. Other studies have also suggested these drugs can help prevent colon cancer, but because they can cause side effects including ulcers and stomach bleeding, experts say it's too soon to recommend them as a routine method of prevention.
"People need to talk to their doctor about whether [NSAIDS] would be helpful for them," said Brooks.
Factors That Increase Risk
The study also identified some lifestyle and medical factors that raised a person's risk of getting colon polyps – and thus, colon cancer.
Of these, smoking was the most serious. Smoking nearly doubled the risk of having polyps. Eating a lot of red meat and having more than one alcoholic drink every day also raised risk.
"These data support relatively simple and safe recommendations that may reduce the risk of colon cancer," said Lieberman. "Stop smoking, reduce alcohol and red meat consumption, take a multivitamin, exercise regularly, and consume vitamin D, calcium, and cereal fiber in your diet."
Regular screening for colon cancer is also important, he noted, especially for people who have a relative who had the disease. In this study, people with a family history of colon cancer had a 66% greater risk of developing colon polyps. Other studies have also found that family history increases the risk of developing colon cancer. For this reason, the American Cancer Society recommends people with a family history begin screening at younger ages (before age 50) and/or get more frequent screenings.
Colon cancer is the fourth most common cancer in the United States, but the second deadliest. ACS estimates that more than 57,000 Americans die from this disease each year; only lung cancer kills more people. Screening can catch changes in the colon before they become cancerous, or find cancer in its early stages, when chances of a cure are better.
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