Probiotic may offer other health benefits, but one receiving more support recently is the possibility of helping to prevent colon cancer. If results of a small but well-controlled study in Ireland are repeated, probiotics – live bacteria that can benefit health – might have a place alongside vegetables, legumes, whole grains and regular exercise in our strategies to lower risk of cancer.

Your digestive tract is home to hundreds of different types of bacteria. Most of them are considered beneficial, crowding out harmful bacteria, speeding digestion and perhaps even enhancing immune function. One of the most accepted health benefits of probiotics comes from taking the probiotics along with or following antibiotic treatment. Antibiotic medicines can sometimes kill the gut’s beneficial bacteria along with the illness-causing bacteria. Without the “good” bacteria in control, sometimes harmful bacteria can multiply, leading to diarrhea. Studies suggest that probiotics restore a healthy bacteria population in the gut and prevent diarrhea.

The recent study focusing on probiotics and colon cancer was published in February. Because colon cancer takes years to develop, the scientists looked at various signs of its early development. This study included 80 people who either had colon cancer tumors or non-cancerous colon polyps (precursors to cancerous tumors) recently removed. Participants were randomly assigned to receive either a probiotic or placebo (an inactive substance). The probiotic contained two types of bacteria often seen as protective of colon health (Lactobacillus rhamnosus and Bifidobacterium) combined with a prebiotic. Prebiotics are nondigestible food ingredients that feed the growth of healthful bacteria in the colon. The combination of probiotics and prebiotics is called synbiotics.

After 12 weeks, researchers found that the balance of colon bacteria had changed in those receiving the synbiotic, with more Lactobacillus and Bifidobacterium and less of the bacteria (Clostridium) that is linked with increasing cancer risk. Compared to patients who received placebos after polyp removal, those who received synbiotics showed decreased DNA damage in the lining of the colon and decreased growth and reproduction of colon cells (which increase in colon cancer). Neither of the groups reported adverse effects of synbiotics. These findings are consistent with earlier studies showing that “bad” bacteria can produce substances that initiate or promote development of colon cancer. Probiotics have been shown to decrease abnormal colon cell development and DNA damage in animals.

Research studies often investigate probiotics using controlled doses of supplements, but you can also get probiotics from foods. Most fresh yogurts contain live, active cultures; check labels to be sure. Drinks that provide probiotics include dairy and soy versions of kefir and acidophilus milk. Fermented soy products (including miso and tempeh) and sauerkraut may also supply probiotics, but little data is available to confirm the amounts or types of bacteria.

What about prebiotics to support growth of healthful bacteria? Inulin (which is extracted from chicory root) and oligofructose are found in prebiotic and synbiotic supplements. But so far research does not show that these prebiotics offer any advantage over the dietary fiber found in vegetables, fruits, whole grains and dried beans.

Probiotic and synbiotic supplements come in capsules, powders and liquids. If you’re going to use one of these products, check the label to be sure you will get at least one billion live bacterium per day. Because supplements are not regulated by the government, look for products with USP-Verified or CL-approved on the label, which means they have undergone testing by the U.S. Pharmocopeia or Consumer Lab, respectively. Probiotic and synbiotic supplements are considered safe, and no health risks have been reported related to their use. Yet benefits are far from certain, especially since results may differ with different types of bacteria. While we wait for more research, use probiotics and/or synbiotics if you wish but make sure to focus on other, more proven cancer prevention strategies, such as exercise, weight control and eating a wide variety of fruits and vegetables.

Hormone replacement therapy

Studies have shown that hormone replacement therapy (HRT) that includes both estrogen and progesterone lowers the risk of colorectal cancer in postmenopausal women. HRT with estrogen alone does not lower the risk. However, hormone use may increase the risk of breast cancer, heart disease, and blood clots.


Polyp removal

Most colorectal polyps are adenomas, which may develop into cancer. The removal of polyps in the colon and rectum may lower the risk of colorectal cancer. Bleeding and infection sometimes occur after polyps are removed during colonoscopy or sigmoidoscopy.

The effect of the following factors on the risk of colorectal cancer is not known:


Nonsteroidal anti-inflammatory drugs (NSAIDs)