For years, consumers have been gulping nutritional supplements containing antioxidants, assuming they protect against cancer. But assumptions don't always turn out well, as a Swedish study finds.
Researchers at Sahlgrenska Academy in Gothenburg, Sweden, found that antioxidants can double the rate of melanoma metastasis in mice. The results reinforce previous findings that antioxidants hasten the progression of lung cancer. Earlier studies found that antioxidants hastened the progression of lung cancer in mice and experiments on human lung cancer cells confirmed the finding.
Given well-established evidence that free radicals can cause cancer, the research community had simply assumed that antioxidants, which destroy them, provide protection against the disease. Found in many nutritional supplements, antioxidants are widely marketed as a means of preventing cancer.
But as a result of the findings, people with cancer or an elevated risk of developing the disease should avoid nutritional supplements that contain antioxidants, according to Professor Martin Bergö, the lead researcher.
Double the rate
The latest study found that antioxidants double the rate of metastasis in malignant melanoma, the most perilous type of skin cancer. Science Translational Medicine published the findings on October 7.
"As opposed to the lung cancer studies, the primary melanoma tumor was not affected," Professor Bergö says. "But the antioxidant boosted the ability of the tumor cells to metastasize, an even more serious problem because metastasis is the cause of death in the case of melanoma. The primary tumor is not dangerous per se and is usually removed."
Experiments on cell cultures from patients with malignant melanoma confirmed the new results.
"We have demonstrated that antioxidants promote the progression of cancer in at least two different ways," Bergö says.
The overall conclusion from the various studies is that antioxidants protect healthy cells from free radicals that can turn them into malignancies but may also protect a tumor once it has developed.
Avoid supplements, lotions
Taking nutritional supplements containing antioxidants may unintentionally hasten the progression of a small tumor or premalignant lesion, neither of which is possible to detect, Bergö said.
"Previous research at Sahlgrenska Academy has indicated that cancer patients are particularly prone to take supplements containing antioxidants," Dr. Bergö says. "Our current research combined with information from large clinical trials with antioxidants suggests that people who have been recently diagnosed with cancer should avoid such supplements."
The role of antioxidants is particularly relevant in the case of melanoma, not only because melanoma cells are known to be sensitive to free radicals but because the cells can be exposed to antioxidants by non-dietary means as well.
"Skin and suntan lotions sometimes contain beta carotene or vitamin E, both of which could potentially affect malignant melanoma cells in the same way as antioxidants in nutritional supplements," Bergö says.