This is one of the most common questions asked by our patients in the oncology clinic, and for most oncologists their knee jerk answer is “NO, It’s NOT safe to take antioxidants during chemotherapy and radiation therapy.”
What’s The Claim?
When I was in my residency, I was taught by my oncology staff and our radiation biologists that antioxidants might interfere with our treatment. As any good little oncology resident would do, I accepted this claim as doctrine.
Here’s The Concern:
Both radiation therapy and many chemotherapy drugs kill cancer by producing molecules, called free radicals, which damage the DNA of tumor cells. Once that DNA damage is created, the tumor cells have a very difficult time trying to fix it…so they die (apoptosis.)
- Most of our cells have a built-in mechanism that signals them to die (apoptosis) when their DNA damage is not fixed quickly.
- Mother Nature is brilliant, as she gave cancer cells defective DNA damage repair capabilities. This slows down their ability to repair DNA damage, making them vulnerable to cell death (apoptosis) signals.
- Normal cells (unlike cancer cells), can efficiently repair DNA damage. This is why radiation and chemotherapy kill cancer cells and not normal cells.
Antioxidants are compounds that have the ability to interact with and inactivate/neutralize free radicals (such as those purposely created by radiation therapy and chemotherapy to kill cancer cells), thereby reducing or eliminating the DNA damaging effects of the free radicals…and thus protecting tumor cells from our cancer treatments.
Here’s Comes The Shocker:
Did you know that there is NOT A SINGLE STUDY that shows that radiation therapy or chemotherapy is less effective when antioxidants are given during those treatments?!
Caveat: Don’t Smoke (Read why in the “Bottom Line” section, below)
In fact, the FDA approved a very potent antioxidant drug (called, Amifostine, WR-2721 or Ethyol®), for the use during radiation therapy and chemotherapy to protect sensitive tissues from the damaging effects of our treatment.
- The FDA approval was based on an extensive review of the data, which found no reduction in the efficacy of radiation therapy or chemotherapy when Amifostine is administered during treatment.
- Amifostine was first developed by the U.S. Army Anti-Radiation Drug Development Program for its ability to protect against damage caused by ionizing radiation.
So, on the one hand we are telling our patients not to take or consume any weak antioxidants (i.e. vitamin E, C, green tea, etc.), and on the other we are prescribing a very potent antioxidant drug to them during their treatment!
Are There Data For Antioxidants Other Than Amifostine?
Since there is no evidence for tumor protection with a very potent antioxidant drug (Amifostine) when administered during radiation therapy or chemotherapy, it seems logical that using weaker antioxidants (such as those found in vitamin supplements, foods and beverages) would have an even lower risk of tumor protection.
Nevertheless, let’s explore the data to see what has been reported…
During my residency, I conducted a study (at the USDA Antioxidant Research Laboratory, Boston MA) to explore whether vitamin E or green tea would interfere with radiation therapy effects on tumors.
I specifically chose these two dietary antioxidant sources, as they are among the most commonly used antioxidants reported by patients undergoing cancer treatments.
I fed hundreds of mice one of three diets:
- normal mouse food (with all the recommended nutrients mice require to be healthy)
- normal mouse food with extra vitamin E (alpha-tocopherol; the amount of vitamin E was equivalent to the human consumption of 400 I.U.’s per day…which is the amount most patients take in their vitamin E supplements.)
- normal mouse food with green tea extract (the extract is called, EGCG, a well-known antioxidant; the amount of EGCG was equivalent to what would be found in the human consumption of 3-4 cups of green tea per day…an amount of green tea that is not unreasonable for most green tea drinkers to consume each day.)
I started the mice on these three diets for a few weeks, and then implanted a breast cancer into their hind legs. Then, I waited for the tumors to grow while the mice continued on their diets.
What Did I Discover?
- I found that the EGCG and VE concentrated 150-220% greater in the tumors than in the surrounding muscle tissue. This means that the tumors gobbled up the antioxidants much more than the surrounding normal tissues. With these findings, I expected to see some dramatic differences in the effects of the diets on tumor growth and responsiveness to radiation.
- Before I radiated the tumors, it was noted that they all grew to the size of a pea at the same rate (so, neither the EGCG nor the vitamin E supplemented diets slowed the tumor growth)
- Neither the EGCG nor vitamin E supplemented diets decreased the effectiveness of radiation therapy
- The tumors that recurred after radiation therapy regrew 25% slower on the EGCG and vitamin E diets.
- The hind legs of the mice on the EGCG and vitamin E diets were significantly protected from the damaging effects of the radiation (much less tissue scarring, fibrosis and necrosis.)
In summary, I found no tumor protection and a significant normal tissue protection with the antioxidant-rich diets.
- No reports of decreased efficacy of chemotherapy for patients using antioxidants during treatment.
- Many studies show reduced side effects and improved treatment tolerance and outcomes with the co-administration of antioxidants during chemotherapy.
Other authors have concluded similar findings in their reviews of the literature for chemotherapy or radiation therapy and antioxidants:
- Multiple dietary antioxidants enhance the efficacy of standard and experimental cancer therapies and decrease their toxicity
- Antioxidants and other nutrients do not interfere with chemotherapy or radiation therapy and can increase anti-cancer activity and patient survival, part 1 (and part 2)
- Should patients undergoing chemotherapy and radiotherapy be prescribed antioxidants?
- Antioxidants and Other Micronutrients in Complementary Oncology
The Bottom Line:
I wrote a review article for the Journal of the National Cancer Institute on this topic, in 2008. The conclusions remain the same, today:
- Although the vast majority of studies show no tumor protection with antioxidants and chemotherapy or radiation, there are a small number of animal and cell studies which have shown a reduced efficacy of radiation therapy and chemotherapy.
- There are no human studies which have reported a reduced efficacy of either chemotherapy or radiation therapy when co-administered with antioxidants.
- Numerous studies have reported reduced side effects and improved treatment tolerance when chemotherapy or radiation therapy is co-administered with antioxidants.
- CAVEAT: DON’T SMOKE! There is a study which reported that patients who smoked during radiation therapy and took vitamin E (alpha-tocepherol) alone or both vitamin E and beta-carotene supplements had worse cancer outcomes (significantly more recurrences.) We know that smoking during radiation therapy reduces the effectiveness of radiation. What we don’t know is whether the higher rate of recurrence in the smokers who used vitamin E (with or without beta-carotene) supplements was simply due to the smoking or the combined effect of smoking with the supplements. What we do know is that the non-smokers who took these supplements during radiation therapy had no increased risk of recurrence compared to those not taking the supplements. Conclusion: Don’t smoke during radiation therapy.
The approaches I recommend today are the following:
Depending on a variety of factors (i.e. the patient’s condition, cancer, stage, type of treatments they received or are receiving, their interest level in using antioxidants, etc.) I counsel patients on either choosing a cautious or less cautious approach.
- Cautious Approach: Avoid high-dose antioxidants during chemotherapy & radiation therapy. Consume your antioxidants through food and beverages (i.e. fruits, vegetables, teas, etc). A multi-vitamin is not likely going to have any significant tumor protection effects. You can resume taking high-dose antioxidants after the completion of chemotherapy or radiation therapy, but first discuss this with your oncology team.
- Less Cautious Approach: Consider taking various antioxidant supplements (along with fruits and vegetables) to improve treatment tolerance and quality of life. Your selection of these antioxidants should be informed by the scientific evidence in the published literature. I strongly recommend that you work with a provider who is very knowledgeable in the safety, indications and potential interactions of these supplements with conventional treatments (i.e. prescribed and over the counter drugs, botanicals, chemotherapy agents, surgery, radiation therapy, etc.) Before starting any new supplement, always discuss this with your oncology team.
What Antioxidants and What Doses Do I Recommend?
No one knows (sorry for the tease.) But this is a great topic for a future blog post, don’t you think?