Antioxidants, also known as “free radical scavengers,” are chemicals that interact with and neutralise free radicals, thus preventing them from causing damage. The human body makes some of the antioxidants, called endogenous antioxidants that it uses to neutralise free radicals, but it relies on external sources, primarily the diet, to obtain the rest of the antioxidants it needs.

External or exogenous antioxidants are commonly called dietary antioxidants and can be found in fruits, vegetables, and grains as well as in certain dietary supplements such as beta-carotene, lycopene, and vitamins A, C, and E.

Antioxidant supplementation during conventional chemotherapy and radiation therapy is a controversial subject, which is why we are including it in our information pages, so that you have a good knowledge-base from which to make an informed decision on its use or not. Some studies suggest taking antioxidants supplements during treatment may be beneficial; however, there are just as many studies that tell us this may be harmful.

Antioxidant Therapy as a Complementary Therapy

The use of antioxidants as a complementary therapy for cancer is highly contentious because while some laboratory evidence from chemical, cell culture, and animal studies indicates that antioxidants may slow or possibly prevent the development of cancer, other studies are not a clear in their results.


There are some concerns that some antioxidants may actually hamper the effectiveness of the radiation therapy or chemotherapy by actually protecting tumour cells, in addition to healthy cells, from the oxidative damage intentionally caused by conventional treatments.

Veronica McLymont, PhD, director of food and nutrition services at Memorial Sloan-Kettering Cancer Center says, “We tell our patients to focus on food. Foods contain a mix of many different antioxidants, along with other nutrients and fibre. The more colourful your diet is the better, since antioxidants and other phytochemicals are often what give fruits and vegetables their colour.”

The best thing to do is to fill your plate with antioxidant-rich foods such as:

  • Berries
  • Leafy green vegetables
  • Sweet peppers
  • Tomatoes


Five large-scale clinical trials published in the 1990s reached differing conclusions about the effect of antioxidants on cancer. The studies examined the effect of beta-carotene and other antioxidants on cancer in different patient groups. However, beta-carotene appeared to have different effects depending upon the patient population. The conclusions of each study are summarized below.


The first large randomised trial on antioxidants and cancer risk was the Chinese Cancer Prevention Study, published in 1993. This trial investigated the effect of a combination of beta-carotene, vitamin E, and selenium on cancer in healthy Chinese men and women at high risk for gastric cancer. The study showed a combination of beta-carotene, vitamin E, and selenium significantly reduced incidence of both gastric cancer and cancer overall.

A 1994 cancer prevention study entitled the Alpha-Tocopherol (vitmain E)/Beta-Carotene Cancer Prevention Study (ATBC) demonstrated that lung cancer rates of Finnish male smokers increased significantly with beta-carotene and were not affected by vitamin E.

Another 1994 study, the Beta-Carotene and Retinol (vitamin A) Efficacy Trial (CARET), also demonstrated a possible increase in lung cancer associated with antioxidants.

The 1996 Physicians’ Health Study I (PHS) found no change in cancer rates associated with beta-carotene and aspirin taken by U.S. male physicians.

The 1999 Women’s Health Study (WHS) tested effects of vitamin E and beta-carotene in the prevention of cancer and cardiovascular disease among women age 45 years or older. Among apparently healthy women, there was no benefit or harm from beta-carotene supplementation. Investigation of the effect of vitamin E is ongoing. (5)

We need more research to definitively settle the question of whether taking antioxidants during cancer treatment is harmful or helpful. It is very likely that antioxidants during cancer treatment may be beneficial for some people, yet harmful for others. No two people, or two cancers, are the same.

How is Antioxidant Therapy Administered?

Some individuals take antioxidant suppleents a a method of boosting their immune system. These come in various formats, including liquid and pills or capsules. Some of these formulae have minerals added.

Many fruits, vegetables, and other foods that are rich in antioxidants lower the risk of heart disease, high blood pressure, some eye diseases, and various forms of cancer.

Getting a single antioxidant from a pill, such as vitamin C or beta carotene, isn’t as protectiveas getting natural antioxidants from fruit and vegetables.

Kim Jordan, RD, nutrition director for the Seattle Cancer Care Alliance says, “The emphasis should be on plant-based foods, not supplements. When you have cancer, it’s important to give your body everything it needs to stay nourished and maintain a healthy immune system. The only way to do that is with a balanced diet of real food.

Side Effects or Risks

There is no evidence to support that antioxidant-rich, whole food or drinks should be avoided during cancer therapy. It is believed that the level of any one particular antioxidant in a whole food is unlikely to interfere with treatment.

Experts do worry that high doses of antioxidants may reduce the effectiveness of chemotherapy.

Please consult your oncology team before to take any vitamin, mineral, and/or herbal supplements during cancer treatment; they will be able to advise you whether it is safe or not and if so, which is the best choice for you.


Please note that the Little Fighters Cancer Trust shares information regarding various types of cancer treatments on this blog merely for informational use. LFCT does not endorse or promote any specific cancer treatments – we believe that the public should be informed but that the option is theirs to take as to what treatments are to be used.

Always consult your medical practitioner prior to taking any other medication, natural or otherwise.