If you’re undergoing cancer treatment, it may be beneficial to take certain vitamin and mineral supplements. Cancer symptoms and treatment side effects can affect your ability to eat and absorb nutrients.

"Depending on the treatment you receive and the severity of your side effects, you may have difficulty eating," says Jeanice Skousen, MDA, RDN, LD, a dietitian at Piedmont Athens Regional. “Taking a multivitamin or other supplements to replete mineral or vitamin deficiencies can be helpful.”

Getting the right vitamins and nutrients is essential during cancer treatment.

“Malnutrition can cause weakness, tiredness and the inability to fight infection or finish cancer treatment,” she says. “And some supplements may help ease certain side effects, like nausea or mouth sores.”

A word of caution: Talk to your oncologist if you currently take any supplements to ensure they won’t interact with your cancer treatments, such as chemotherapy, immunotherapy, radiation therapy and surgery. You should also check with your oncologist before taking any new supplements. You can also ask them to order a blood test to check your vitamin levels for deficiencies. 

“If you have cancer, it’s natural to want to do everything you can to promote survival and reduce your risk of recurrence,” says Skousen. “However, supplementation isn’t always necessary. It depends on your diagnosis, the treatment you’re receiving, your nutrient levels and if you’re able to eat a well-balanced, nutritious diet.”

Supplements during cancer treatment

“If you have cancer, it’s important to have your doctor or dietitian evaluate your individual needs according to your specific diagnosis, symptoms and treatments,” says Skousen.

Here are some supplements your oncologist or dietitian may recommend:

• Multivitamin: Generally, multivitamins are safe and beneficial for most people with cancer and other individuals, she says. They can help ensure you’re meeting your baseline nutrient needs.

• Vitamin D: Research shows that vitamin D sufficiency is important for overall health and cancer prevention. If your blood levels are low, supplementation may be beneficial because of vitamin D’s protective role in reducing inflammation and improving immune function.

• Glutamine: Glutamine may reduce inflammatory side effects during treatment, such as mouth sores.

• Ginger: Ginger can be helpful for the management of nausea. Skousen doesn’t typically recommend ginger pills or extracts, but instead suggests taking ginger in fresh, dried, crystallized or candied forms.

• Iron: Your oncologist may recommend an iron supplement if your treatment causes low hemoglobin levels.

• Vitamin B12: Some chemotherapy regimens can cause peripheral neuropathy, which is numbness and tingling in the hands and feet. Supplementing with vitamin B12 may help relieve these side effects.  

• Probiotics: Probiotics can be helpful for patients with gastrointestinal symptoms. However, Skousen recommends talking with your doctor or dietitian before taking probiotics. If you have low white blood cell counts, you may need to avoid sources of live bacteria that could increase your risk of infection.

What to look for when choosing a supplement

Skousen advises choosing supplements that have been individually tested and certified by a nonprofit program, such as NSF International or USP. Products labeled with these certifications are more likely to be high quality, she says.

“These organizations test for quality, purity and freedom from contaminants,” she says. “Their seal helps you know that the supplement contains what its label says it contains, that it disintegrates properly in the body and has been produced in accordance with good manufacturing processes in a certified facility.”

Supplements to avoid during cancer treatment

Skousen recommends avoiding antioxidant supplements during cancer treatment because of the potential for tumor protection and reduced survival. 

“Taking antioxidant supplements may protect the cancer cells that the treatment is trying to destroy,” she says.

Antioxidant supplements include:

• Vitamin A

• Vitamin C

• Vitamin E

• Selenium

• Coenzyme Q10 (CoQ10)

She notes that it’s safe to consume whole-food sources of antioxidants during treatment.

“Whole foods don’t contain similarly large amounts of antioxidative nutrients that a single-dose vitamin supplement would,” she says. “Many nutritious fruits and vegetables are great sources of antioxidants (such as berries, spinach, tomatoes, and broccoli). Include these foods as tolerated.”

She also recommends avoiding St. John’s wort supplements, which can interfere with how certain chemotherapies work.

Other supplements—like high-dose beta-carotene—may increase cancer risk. That’s why it’s crucial to talk to your oncologist or dietitian before taking any supplements.

“Research shows that individuals who smoke and take high-dose beta-carotene supplements are at an increased risk for lung cancer,” she says.

If you’re planning to undergo surgery, it’s important to avoid supplements that increase your bleeding risk, such as garlic extract, ginseng and fish oil.

“It’s also important that you understand why you need to take a supplement, how much you should take and for how long you should take it,” says Skousen.

How are vitamins and supplements regulated?

“You may see a lot on the internet or hear from friends about certain supplements, but it’s important to know that supplements aren’t regulated in the same way as over-the-counter medications,” says Skousen. “Just because it’s on the shelf at the store or available online doesn’t mean it does what it claims to do.”

The Food and Drug Administration (FDA) is in charge of regulating supplements, she explains.

“In general, the FDA considers medications unsafe until they are proven safe in clinical trials. Medications go through a lot of testing,” says Skousen. “However, it’s almost the opposite for supplements: They can be sold online and in stores without manufactures having to prove that they’re safe as long as they don’t claim to diagnose, prevent or cure disease. The FDA only steps in if it gets reports that a supplement has caused harm. And that’s only after a product has been on the market.”

The bottom line: “If it sounds too good to be true, it probably is.”

Getting nutrients from whole-food sources

Skousen says getting your vitamins and minerals from whole-food sources is best.

“Research shows that supplementation with a particular nutrient may be beneficial for people with low dietary intakes or blood levels of that nutrient,” she says. “But supplementation may have no effect or even be harmful if you already have adequate levels of that nutrient through healthy and fortified foods.”

She adds, “Getting your nutrients from food and eating a well-balanced diet with fruits, vegetables, herbs and spices is generally safer and better absorbed by the body than taking vitamins and minerals in supplement form.”

Check out more nutrition tips from Cancer Wellness experts.