Harvard Health Letter

5 simple steps that may help prevent colorectal cancer

Screenings, exercise, and vitamin D may reduce your risks.

Colorectal cancer is the fourth most common cancer in the United States. It refers to cancer of either the colon, also known as the large intestine, or the rectum, the last six inches of the digestive system. There's no guaranteed way to prevent the disease, but Dr. Charles Fuchs, director of the Gastrointestinal Cancer Center at Harvard-affiliated Dana-Farber Cancer Institute, says the following steps may help.

1 Get a screening

A colonoscopy allows a gastroenterologist to examine the inside of your colon and rectum, and also remove cancerous or precancerous tumors. "There's no question that a colonoscopy is the best test," says Dr. Fuchs. The National Cancer Institute recommends colonoscopy screenings for all adults starting at age 50, with follow-ups every 10 years, or more often if the risk for cancer is higher. People with a parent or sibling who had colon cancer should be screened before age 50.

2 Consider aspirin

A randomized study showed last year that daily aspirin use reduces the risk for developing colorectal cancer by 20%. "It's not recommended for widespread use because aspirin has a risk of gastrointestinal bleeding and ulcer formation. But someone with an obvious colorectal cancer risk may benefit from one 325-milligram dose per day. Talk to your doctor to weigh the risks and benefits," says Dr. Fuchs.

3 Take vitamin D

Dr. Fuchs' research shows that people with a blood level of vitamin D below 20 ng/ml are at an increased risk for developing colorectal cancer, whereas individuals with a vitamin D level greater than 30 ng/ml experience a lower risk of colorectal cancer. However, we don't know yet if taking vitamin D reduces risk. Dr. Fuchs is about to study the issue. Still, he recommends taking 2,000-IU of vitamin D per day.

Know your risk factors

  • Age (50 and older)

  • Family history of colorectal cancer

  • Frequent red meat intake

  • Heavy alcohol use

  • History of inflammatory bowel disease

  • History of polyps

  • Low vitamin D levels

  • Obesity

  • Sedentary lifestyle

  • Smoking

  • Type two diabetes

4 Watch your diet

A growing body of evidence suggests that dietary habits can substantially influence your risk for colorectal cancer. Chief among them: eating red meat such as beef, lamb, and pork, and processed meat such as bacon. "We think it's because of nitrogen-based compounds in the meat called heterocyclic amines, which are generated in the cooking process. Charring meat can make this worse," says Dr. Fuchs. He recommends no more than two servings of red meat as a main dish per week. Alcohol consumption is also linked to an increased risk of colorectal cancer, so Dr. Fuchs advises an intake limit of no more than one drink per day for women and no more than two drinks per day for men. And high-glycemic diets, which spike blood sugar, may also increase colorectal cancer risk. "Too much blood sugar forces your body to make more insulin, the hormone that helps cells use energy, and we know that insulin has a growth-promoting affect on cancer," says Dr. Fuchs.

5 Exercise

There's no absolute proof that exercising reduces the risk of colorectal cancer, but Dr. Fuchs says there are at least 52 studies showing an association between the two. "The connection makes sense; if you're obese and you're sedentary, you'll make more insulin. If you exercise, you'll make less," he says. Aim for 150 minutes per week of moderate-intensity exercise, such as brisk walking.

The truth about fiber

It doesn't prevent colorectal cancer, but it may prevent heart disease and diabetes.

Doctors used to believe that a diet rich in fiber would help prevent colorectal cancer. However, several large studies, including one from Harvard, found that high fiber intake offered no protection against this form of cancer.

But fiber is still important for digestive health, and it can relieve constipation. Greater fiber intake is also associated with a lower risk of developing heart disease and type 2 diabetes. A study published Dec. 19, 2013, in BMJ found a significantly lower risk of heart disease with every additional 7 grams per day of total fiber intake. The Institute of Medicine recommends that women ages 50 and older get 21 grams per day; men ages 50 and older should get 30 grams per day. It's best to get fiber from foods, such as beans, whole grains, vegetables, and fruits.

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