Can Probiotics Be Harmful to Cancer Patients?

Your body naturally harbors a certain amount of bacteria that do not cause health problems. Instead, these bacteria have adapted to help the human body. Probiotic supplements should be used with care in cancer patients, because although they can have some benefits for health they may also be dangerous for people with a weakened immune system.

Senior woman taking a pill (Image: curtoicurto/iStock/Getty Images)

Probiotics and Acidophilus

Probiotics are microorganisms that, when ingested in sufficient amounts, can benefit the human body, the National Center for Complementary and Alternative Medicine explains. Most probiotic supplements contain bacteria, such as Lactobacillus acidophilus or Bifidobacteria, though some strains of yeast are used as probiotics. These supplements contain bacteria similar to the microorganisms in the digestive tract and replenish or boost helpful bacteria.


Bacteria that live in your digestive tract are beneficial for your health. Not only do these bacteria help you digest food, but they keep infectious bacteria from colonizing your intestines, by taking up space and resources that would otherwise be used by infectious bacteria, the University of Maryland Medical Center explains. Probiotic supplements can be taken in capsule or tablet forms and are also in some foods, such as milk and yogurt.

Benefits for Cancer Patients

Sometimes probiotics are used to help cancer patients. Probiotics stimulate the immune system and some believe that probiotics eliminate carcinogens and directly kill tumor cells, the American Cancer Society explains. In theory, these bacteria also secrete B vitamins and vitamin K, which may slow tumor growth. Studies examining the effects of probiotics on cancer risk have yielded mixed results; probiotics may be able to reduce your risk of developing colon, breast and other types of cancer, but the evidence is not clear.


If you have cancer and are undergoing treatment, talk to your doctor before taking probiotics. Although probiotics are generally not infectious and do not cause tissue damage, they can be dangerous if you have a severely weakened immune system, the University of Maryland Medical Center reports. Many therapies for cancer, such as radiation and chemotherapy, damage your immune system, which could allow these bacteria to spread to other tissues and cause problems, such as sepsis.

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