Hello Alice,
Antioxidant Controversy
Using antioxidant supplements during radiation therapy is controversial. The controversy is due to concerns that the concentrated antioxidants in supplements may interfere with how radiation therapy kills cancer cells. It is important to note that these concerns are focused on antioxidant supplements, not on the antioxidants found naturally in healthy food and drinks.
In other words, antioxidants from food and beverages such as vegetables, fruit, green and black tea, and whole grains are fine to have during radiation therapy. Antioxidant supplements on the other hand, such as beta-carotene, vitamin E, and vitamin C may be a problem.
Radiation Therapy
One of the ways in which radiation therapy is believed to work is by creating free radicals, which then damage the cancer cells and cause them to die. Free radicals also are called oxidants. In theory, if radiation therapy creates oxidants (free radicals), then higher doses of antioxidant supplements may interfere with how these oxidants kill cancer cells.
Research
You probably noticed that I used the words "in theory" to describe how antioxidant supplements may interfere with radiation therapy. This is because it is not proven that antioxidant supplements lessen the effectiveness of radiation therapy. In fact, some healthcare providers believe that antioxidant supplements will protect healthy cells during treatment, while allowing the radiation to kill unhealthy, cancer cells. This isn't proven either.
Considering these two competing theories, it is important to look at what the research tells us. Unfortunately, there aren't a lot of long-term, well-controlled, human studies on the risks and benefits of antioxidant supplements during radiation therapy. Further complicating this picture is that there are dozens antioxidant supplements, each of which may have different actions in the body and may or may not interact with radiation therapy.
There are some small studies that suggest that taking antioxidant supplements such as vitamin C can decrease the severity of symptoms in people undergoing cancer treatment, including radiation therapy. This seems to support the idea that antioxidant supplements may protect healthy cells during cancer treatment.
However, this doesn't tell us anything about whether these supplements may have interfered with radiation therapy. In order to learn the answer to this question, it is important to follow people who have taken antioxidant supplements during treatment over several years to see if they have cancer recurrence at a rate similar to people who did not use these supplements. In other words, only over time would we be able to tell whether or not antioxidant supplements decreased the effectiveness of radiation therapy.
On the other side, there is one larger study that suggests that antioxidant supplements may interfere with the effectiveness of cancer treatment. In this study, 540 patients with stage I or II head and neck cancer were randomly assigned to take either a beta-carotene and vitamin E supplement or a placebo during and after radiation therapy. A placebo looks like a medication, in this case a dietary supplement, but it does not contain any active ingredients.
After 3.5 years, those people who took the supplements had nearly 2 times the risk of cancer recurrence (getting their cancer again), and about 3 times the risk of getting a new, different cancer. In summary, in this study, taking the antioxidant supplements, in particular vitamin E, appeared to increase the risk of cancer recurrence and getting another, new cancer. This suggests that the antioxidant supplement made radiation therapy less effective.
Antioxidants or Not?
When considering the limited research available on antioxidant supplements during radiation therapy, the only conclusion we can reach is that we simply do not know if taking antioxidant supplements is helpful or harmful. I believe that the situation is much more complicated than simply antioxidant supplements vs. no antioxidant supplements during radiation therapy, or any cancer treatment.
There are dozens of antioxidants that can be taken as dietary supplements, and each one can have different actions in the body. Some supplements may interact with radiation therapy, while others may not. Some antioxidant supplements may be helpful for certain cancer types, yet harmful for others. We simply do not have enough information to know with certainty who should or should not take any particular antioxidant supplement during cancer treatment.
Furthermore, two very large studies that followed tens of thousands of people have shown that some antioxidant supplements, including beta-carotene and vitamin E, can have opposite effects in different people. For example, beta-carotene appears to increase risk of cancer in smokers and former smokers, yet may decrease risk in people who do not smoke or drink alcohol. These studies clearly suggest that individual risk factors play a role in determining who benefits from or is harmed by antioxidant supplements.
Personal Choices
Until long-term, well-controlled trials are conducted for each different antioxidant supplement in a variety of cancer patient groups, the most conservative approach is to avoid using these supplements during cancer treatment.
However, many individuals with cancer want to try these supplements before this research is available. In these cases, it is important to discuss these issues with the entire health care team. A helpful healthcare provider such as a dietitian, pharmacist, physician, or nurse can help a patient search for any available information about a particular supplement of interest. This can help each patient make an informed decision and ensure that the full treatment team is aware of the patient's choices regarding use of dietary supplements.
Some individuals with cancer make a compromise. They decide to use dietary supplements, but wait until treatment is completed. Given the lack of available evidence, they make the conservative choice during treatment, but then add in dietary supplements once treatment is completed.
Finally, other factors, such as stage of disease and availability of proven conventional treatments can affect a person's decision regarding dietary supplement use during treatment.
The bottom line is that there is not enough evidence to know with certainty that antioxidant supplements will help or harm a person during radiation therapy. The conservative choice is to avoid these products, at least until treatment is completed.
Nutritionist Suzanne
Suzanne Dixon, MPH, MS, RD