High Dose Antioxidants may decrease the effectiveness of Chemotherapy and Radiation Treatment

Wednesday, September 21, 2005

Many cancer patients take dietary supplements, particularly antioxidants, hoping to reduce the adverse effects of chemotherapy and Radiation therapy. Some researchers have even asserted that antioxidants enhance the effectiveness of these therapies. No study to date has shown a clear cut benefit and some have suggested possible harm. A review paper by Dr. Gabriella D'Andrea from the Sloan-Kettering Cancer Center in New York published this week in CA: A Cancer Journal for Clinicians reviews the current studies on antioxidants and concludes that they should be avoided until a clinical study shows a benefit.

Antioxidants like vitamin E, Beta-Carotene and Vitamin C have often been identified as substances that may reduce the risk of some types of cancers. The lower rates of cancer among people who eat lots of fruits and vegetables is often attributed to the fact that fruits and vegetables contain many antioxidants.

Antioxidants reduce the damage to cells done by highly reactive molecules called free radicals. Antioxidants have been recommended by some to help reduce the adverse effects of chemotherapy and radiation therapy.

A study published earlier this year suggests that some antioxidants may be harmful when cancer patients are undergoing radiation therapy. The antioxidants may actually be protecting the tumor from damage.

Ionizing radiation as well as some chemotherapeutic agents actually produce free-radicals which hopefully destroy the tumor. Many methods exist for targeting the tumor such as giving the patient medications like monoclonal antibodies that search for the tumor in the body and attach to it. These antibodies sometimes are attached to a chemical sensitizer that radiation activates to kill the tumor. Cells that are quickly dividing (like cancer) are more sensitive to radiation than other body cells.

In the study the researchers gave patients who had were treated for early stage head or neck tumor Beta Carotene and/or Vitamin E. The Beta Carotene arm of the study was discontinued for ethical concerns because it appeared that patients in another study had higher rates of lung cancer among smokers when they took beta-carotene. The researchers ended up with two groups. One taking 400 units of vitamin E daily and the other group taking placebo.

The Vitamin E group showed a decrease in the adverse effects of radiation therapy (a good thing) but an increase in the recurrence of cancer (a bad thing).

This study needs to be repeated with a number of additional variables before we can generalize to the rest of the cancer population including mesothelioma. First we need to know if there is something about the dose. Another arm at the low dose of 100-200 units of vitamin E might be useful as well as expanding the study to a much broader range of cancers, each with enough participants to yield statistically significant results. Other commonly self prescribed antioxidants could also be incorporated.

The jury is still out, however the results of this study should give patients some pause when considering high dose antioxidants during radiation treatment. A study