Vitamin C and E Supplements Post Stem Cell Transplant
Review of J Am Diet Assoc. 2003;103(8):982-90.
A study in the Journal of the American Dietetic Association looked at use of vitamin C and vitamin E dietary supplements (pills) after stem cell transplant to treat cancer. Stem cell transplant is a type of treatment for more advanced forms of some types of cancer. This study suggests that:
- In people undergoing stem cell transplant for the treatment of breast cancer, using a vitamin C dietary supplement may decrease the risk of recurrence of breast cancer.
- In people undergoing stem cell transplant for the treatment of acute leukemia, using a vitamin C dietary supplement may increase the risk of leukemia recurrence and death after stem cell transplant.
- In people undergoing stem cell transplant for the treatment of breast cancer, using vitamin E dietary supplements has no effect on the risk of disease recurrence or death.
- In people undergoing stem cell transplant for the treatment of acute leukemia, using a vitamin E dietary supplement may increase the risk of leukemia recurrence or death after stem cell transplant.
We provide practical information on what these results mean. Information provided by this type of research may help individuals who are being treated for cancer to make more informed choices about how best to manage their nutritional needs.
Many research studies consistently tell us that a healthy diet and good nutrition (food) can decrease the risk of cancer (1-14). The research is not as consistent on how dietary supplements (pills) may affect cancer risk (15-33). In other words, some research tells us that dietary supplements may decrease cancer risk, but other studies show that certain dietary supplements can increase cancer risk. There is even less information on the possible benefits and risks of taking dietary supplements after a cancer diagnosis (34-38). Again, some studies show that dietary supplements may be helpful, while other research suggests that dietary supplements may be harmful for individuals with a history of cancer. For this reason, it is important that researchers continue to study this topic.
A study in the Journal of the American Dietetic Association looked at use of dietary supplements (pills) after stem cell transplant for the treatment of cancer (39). Stem cell transplant is a type of treatment for more advanced forms of some types of cancer. It is hoped that this type of research will identify dietary and nutrition factors that may increase or decrease survival after cancer. Factors such as age and genetics cannot be changed, but diet and nutrition can! This type of information will allow people to take concrete and practical steps that may improve health and survival after cancer.
What The Researchers Studied
For this study (39), researchers collected information on dietary supplement use from 1,182 people who were scheduled to undergo stem cell transplant for the treatment of cancer. Information on other important factors, including age, gender, type of cancer, type of stem cell transplant, and complications of treatment. The researchers followed up with these people for two years to see whether or not use of dietary supplements affected the risk of relapse (getting cancer again) or death.
What The Study Found
First, the researchers found that people who received a stem cell transplant for breast cancer treatment and reported using a vitamin C supplement of 500 milligrams (mg) or more per day had 89% lower risk (0.11 times the risk) of recurrence when compared to people not using vitamin C. In other words, in breast cancer patients undergoing stem cell transplant, vitamin C dietary supplements seemed to decrease the risk of getting breast cancer again.
Second, the researchers found that people who received a stem cell transplant for the treatment of acute leukemia and reported using a vitamin C dietary supplement of 500 mg or more per day had 63% higher risk (1.63 times the risk) of relapse when compared to people not using vitamin C. In other words, in acute leukemia patients undergoing stem cell transplant, vitamin C dietary supplements seemed to increase the risk of getting leukemia again.
Third, the researchers found that people who received a stem cell transplant for the treatment of acute leukemia and reported using a vitamin C dietary supplement of 500 mg or more per day had 2.25 times (225%) higher risk of death from causes other than relapse when compared to people not using vitamin C. In other words, in patients with acute leukemia undergoing stem cell transplant, vitamin C dietary supplements seemed to increase the risk death from non-relapse causes such as complications of treatment.
Fourth, in people undergoing stem cell transplant for the treatment of breast cancer, using vitamin E dietary supplements has no effect on the risk of disease recurrence or death. In other words, vitamin E dietary supplements did not provide benefit or cause harm in people undergoing stem cell transplant for breast cancer treatment.
Finally, the researchers found that people who received a stem cell transplant for the treatment of acute leukemia and reported using a vitamin E dietary supplement of 400 International Units (IU) or more per day had 77% higher risk (1.77 times the risk) of relapse or death when compared to people not using vitamin E. In other words, in acute leukemia patients undergoing stem cell transplant, vitamin E dietary supplements seemed to increase the risk of getting leukemia again or dying from any cause.
Dietary vitamin C supplements (pills) appeared to provide benefit to people receiving stem cell transplants for breast cancer treatment. Vitamin E supplements did not appear to provide benefit or cause harm in these people.
Both vitamin C and vitamin E supplements (pills) appeared to cause more harm than good in people receiving stem cell transplants for acute leukemia.
What do these results mean?
If we assume that the people in this study are like most people who are undergoing stem cell transplant for the treatment of cancer, then this study suggests that vitamin C dietary supplements may be beneficial to people being treated for breast cancer. For people undergoing stem cell transplant for acute leukemia, both vitamin C and vitamin E dietary supplements appear to cause more harm than good.
However, before we decide what these results mean, it is important to consider some of the limitations and weaknesses of this type of study.
One concern with this type of research is that the results cannot prove cause and effect. The study only tells us that there is an association between certain dietary supplements and risk of relapse or death after a stem cell transplant. It is important to remember that an association is not causation (cause and effect). In other words, we cannot jump to the conclusion that the dietary supplements caused these findings. There are many other factors that could account for or explain these results.
As well, the researchers did not actually assign people in the study to receive or not receive different dietary supplements. Instead, they simply observed who reported taking dietary supplements and how this information was related to outcome after a stem cell transplant. This is called an observational study and it can have many flaws.
Another issue with this type of research is bias, which can lead to incorrect conclusions. For example, we know that women with breast cancer who use dietary supplements also are more likely to be thinner, to eat healthier and to exercise more than non-supplement users (38,40,41). These other factors may explain why the people who were undergoing stem cell transplant for breast cancer and who reported using vitamin C supplements had lower risk of breast cancer recurrence and death. The researchers did not examine these other factors, so there is no way to know for certain that the results weren't affected by these things.
Another source of bias can come from how the information on supplement use was collected. Simply asking people about their supplement use can cause bias. Sometimes people provide incorrect information by mistake (42,43).
Finally, keep in mind that the researchers only asked the people in this study about their use of dietary supplements at one point in time. And they only asked about this before each person received a stem cell transplant. This doesn't give us any information about how using dietary supplements after a stem cell transplant or over the long-term may be related to cancer recurrence or risk of death.
These potential problems do not mean that the study is no good. But it is important to keep these factors in mind when you decide what these results mean for you.
Putting It All Together
Keep the following points in mind as you decide whether dietary supplements are right for you after a diagnosis of cancer:
- This study highlights that a 'one size fits all' approach is not ideal when it comes to cancer. Nutrition is very complex. What is a good approach for one person may not be good for someone else. This is especially true for cancer.
- Vitamin C seemed to be beneficial for people receiving stem cell transplant for breast cancer, yet it appeared to cause harm in people undergoing this procedure to treat acute leukemia.
- Before you decide to use dietary supplements think about the type of disease that you have, the type of treatment you will be receiving, other health conditions you may have, your family history of disease, your current diet, your level of exercise, and many, many other factors.
Stem Cell Transplant For Breast Cancer
- If you are being treated for breast cancer, a vitamin C dietary supplement may be of benefit to you. At least one other study suggests that taking vitamin C and possibly vitamin E after a diagnosis of breast cancer may provide benefits to health (34). However, keep in mind that in general, using higher doses or more antioxidants does not appear to provide more benefit.
- Some studies tell us that high doses of antioxidants increase risk of cancer and precancerous conditions, instead of decreasing risk (22,25,44). For this reason, it is wise to use moderate doses of dietary supplements.
- What is a moderate dose? Many health experts suggest taking no more than two to three times the Recommended Dietary Allowance (RDA) or Dietary Reference Intake (DRI) for any one nutrient.
- The DRI for vitamin C for adult women is 75 mg per day (45). This means that two to three times the DRI is 150 to 225 mg of vitamin C per day. The study we reviewed here tells us that 500 mg of vitamin C per day is enough to see benefit. Health experts have set a safe upper limit (UL) of intake for vitamin C as 2000 mg per day (45). The UL is the amount of a nutrient that can be taken with low risk of negative (harmful) side effects.
- Bottom Line: Taking about 500 mg of vitamin C daily in a dietary supplement may be beneficial if you've had a stem cell transplant for breast cancer. More is not better. A supplement that provides about 500 mg of vitamin C daily likely will provide any possible benefits, without risk of getting too much of this nutrient.
Stem Cell Transplant For Acute Leukemia
Fitting Vitamin C Into The Diet
Regardless of whether you decide to use vitamin C or any other dietary supplement, keep in mind that getting nutrients from foods is still a very safe way to improve health and possibly lower risk of cancer and cancer recurrence. Use the following table to focus on food sources of vitamin C in your diet**.
Some Food Sources of Vitamin C (46)
Vitamin C in milligrams (mg)
|Sweet Red Peppers, raw
||8 ounces (1 cup)
|Peaches, frozen, sliced
||8 ounces (1 cup)
||8 ounces (1 cup)
|Sweet Green Peppers, raw
|Strawberries, frozen, sliced
|Peas, in pod
** A stem cell transplant will decrease immune function. This can make a person more likely to develop a food-related infection (food borne illness). For this reason, people who have received a stem cell transplant may need to follow very specific dietary guidelines to avoid getting sick. Examples of this type of dietary guidelines can be seen at Diet Guidelines for Immunosuppressed Patients. It is very important that you work with your health care team to learn about the particular diet that you need to follow as part of your cancer treatment!
NOTE: If you are in cancer treatment, these diet changes may not be right for you.
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Publish Date: 01/2005
This content was last reviewed
August 15, 2010 by Dr. Reshma L. Mahtani.