Cancer survivors are turning to nutritional supplements much more often than the general population, but those supplements may be doing more harm than good, a study showed.
While vitamin and mineral supplements may help some cancer patients - those who cannot eat a balanced diet, for example - others may interfere with prescribed cancer treatments or even encourage the growth of the cancer, said Dr Cornelia Ulrich of the Fred Hutchinson Cancer Research Centre in Seattle.
"They nearly always assume that it's beneficial to take supplements. What's concerning about that is that some research suggests that it may not be beneficial," Ulrich said.
In research funded by the National Cancer Institute and published this month in the Journal of Clinical Oncology, Ulrich and Dr Christine Velicer reviewed 32 studies published between 1999 and 2006.
They found that 64 to 81 per cent of cancer survivors take vitamin and mineral supplements, compared to only 50 per cent of adults in the general population. That includes multivitamins as well as other supplements like megadoses of specific vitamins and herbal treatments.
Breast cancer survivors reported the highest percentage of supplement use, from 75 to 87 percent, where prostate cancer survivors reported the lowest, from 26 to 35 per cent.
It was not clear if this difference was because women more frequently use nutritional supplements in general or if another factor was at play, Ulrich said. Highly educated women were most likely to use supplements, the research found.
The research also showed that people were more likely to initiate supplement use after a cancer diagnosis: between 14 and 32 percent of patients began taking supplements after they learned they had cancer. The patients began supplement use for a variety of reasons, Ulrich said. Some hoped to strengthen their immune system while others used supplements to help them deal with the stress of the diagnosis and its treatment.
One problem is that many people don't inform their doctors that they're taking supplements. Even if they do, their physicians may not record the information: up to 68 per cent of physicians in the studies reviewed weren't aware of supplement use by their patients. "There's a discrepancy between what patients actually take and what physicians know or document that they take," Ulrich said.
Thirty-one to 68 per cent of adults with cancer didn't volunteer information on their supplement use to their doctors or their doctors didn't write the information in their medical records.
This is of concern because the use of supplements could have side effects and counterindications with other medications, Ulrich said. There is a lack of sufficient research on the effects of different supplements on cancer survivors, positive or negative, she said. For example, St. John's Wort may interfere with chemotherapy.
In reviewing the studies, the researchers came to four conclusions. It was clear that adult cancer survivors had a high incidence of supplement use; what was not clear is whether or not that supplement use was helpful. The physicians for these patients often don't know about -- or don't document -- their use of vitamin and mineral supplements. And with the supplements being so popular among this group of people, more research and resources should be devoted to determining their effects.
"Knowing that patients take supplements, it's very important that we do well-defined studies to see if they improve their quality of life, their survival, their risk of having recurrences." Considering that we know how many cancer patients and survivors do take supplements, she said, it's surprising that there is not more research specifically focused on them, especially when recent studies suggest that some supplements may actually interfere with their treatment.
"It's very interesting that there may be some nutrients that are beneficial in some respects but then harmful in other respects or at different doses," Ulrich said. "Some is good, more is not always better."
Because the research is minimal and inconclusive, the advice to cancer patients about supplement use is often confusing, Ulrich and Velicer wrote in their review.
The American Cancer Society warns patients that taking supplements during cancer treatment is controversial and might be harmful, but also says that a multivitamin is of benefit to anyone who cannot eat a healthy diet. The National Cancer Institute recommends that patients avoid supplement use during cancer treatment, unless advised otherwise by their doctor.
One supplement of particular interest is folic acid, a nutrient commonly found in food, Ulrich said. A Tufts University study published last summer showed there may be a link between folic acid fortification and rates of colon cancer in Canada and the United States. There is concern that folic acid supplements may actually speed up the growth of tumours, and Ulrich's team is looking into grant funding to study that possibility. "That's, I think, one area where we really have to learn more."
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