Antioxidants are substances that can help protect cells from damage caused by free radicals, or unstable molecules. That damage, called “oxidative stress,” is linked to the kind of damage in DNA mutations that can contribute to the risk of certain cancers, as well as diabetes, Alzheimer’s disease, and Parkinson’s disease.
Some studies have shown that taking antioxidant supplements – such as vitamins A, C, E, folic acid, and beta-carotene – might help reduce the risk for certain diseases related to oxidative stress, including cancer. A 1993 clinical trial from China found “significantly reduced” stomach cancer mortality rates in participants who took beta-carotene, vitamin E, and selenium over a five-year period.
However, another study found that elevated antioxidant levels might heighten the risk for certain types of cancer. In a 1994 Swedish trial, male smokers who took beta-carotene regularly were more likely to develop lung cancer than male smokers who did not take the supplement. Researchers concluded that the supplements they studied could possibly have both harmful and beneficial effects.
To date, nine randomized controlled clinical trials of dietary antioxidant supplements for cancer prevention have been conducted worldwide to study the effects of antioxidant supplements and cancer. The different studies reached varying conclusions about the efficacy and safety of taking antioxidant supplements to help prevent cancer or taking them during cancer treatment. “Additional large randomized controlled trials are needed to provide clear scientific evidence about the potential benefits or harms of taking antioxidant supplements during cancer treatment,” the National Cancer Institute (NCI), reports.
While the Chinese and Swedish studies found that antioxidants could decrease or increase cancer risk, respectively, other studies found that antioxidant supplements had no effect on cancer risk. The 2005 Women’s Health Study concluded that there was “no benefit or harm associated with two years of beta-carotene supplementation” in regards to cancer and cardiovascular disease risk in women 45 or older.
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Antioxidant supplements have also been shown to decrease the effectiveness of certain cancer treatments. Some treatments, such as radiation and certain forms of chemotherapy, use free radicals to kill cancer cells. But because antioxidant supplements work by combating free radicals, taking supplements as a cancer patient may lessen the effectiveness of certain cancer treatments, some studies have stated. However, getting antioxidants from foods like fruits, vegetables, and grains, which are rich sources of dietary antioxidants, does not reduce the potency of treatment. They also help provide nutrients that support a healthy immune system.
It’s important to discuss all supplements with your doctor, including antioxidants, before beginning a regimen, especially during active cancer treatment.
In most cases, you can find all the antioxidants you need in a healthy, plant-based diet. Eating plenty of differently colored fruits and vegetables can help ensure you get important antioxidants like lycopene, beta-carotene, and anthocyanins.