The supermarket labels touting the benefits of antioxidant-rich foods such as frozen berries and green tea are so ubiquitous that many people assume that taking extra doses in the form of supplements is beneficial. But a growing body of evidence, including a study published Wednesday, suggests that high doses may do more harm than good in patients with certain types of cancer.
Researchers in Sweden gave Vitamin E supplements and a drug called acetylcysteine to mice with early stages of lung cancer, expecting them to slow the tumors’ growth. Instead, the opposite occurred — the tumors multiplied and grew more aggressively.
Cancer researchers cautioned that more studies need to be done in humans before they can make general recommendations about the use of antioxidant supplements. But the new research complements a groundbreaking 1994 National Cancer Institute study that showed an increase in incidence of lung cancer among smokers who took supplements of the antioxidant called beta-carotene.
Editors at the journal Science Translational Medicine, which published the mouse study, called the findings “the dark side of antioxidants.”
Antioxidants are chemical compounds — such as vitamins A, C and E, and lycopene — that prevent or delay damage to cells or genetic material by stopping the buildup of what’s known as “free radicals” that contribute to disease. Researchers believe there are hundreds or even thousands of different substances that can act in this manner.
A number of studies have found that eating fruits and vegetables rich in antioxidants helps lower the risk of chronic diseases, as well as the effects of aging (although there’s debate about whether it is really the antioxidants or a combination of antioxidants, minerals and fiber or something else entirely in the food).
But the effect of high-dose supplements has been less clear. Most studies have disappointed researchers hoping to find a disease-fighting silver bullet in antioxidants. A large study involving Vitamin E supplements in patients with heart disease or at high risk for getting it generally showed no effect.
Other research has shown that taking large amounts of Vitamin E does not prevent prostate cancer. Supplements have also been shown to interact with some medicines. One study showed that the supplements may also interfere with radiation and some types of chemotherapy in breast cancer patients.
Martin Bergo, a researcher at the University of Gothenburg in Sweden who is one of the authors of the mouse study, said his team found that antioxidants appear to decrease the amount of a protein called p53, an important part of the body’s defense system against cancer that aids in the suppression of tumors. The deficiency of that protein may speed up cancer progression, he said.
Zachary T. Schafer, an assistant professor of cancer biology at Notre Dame who studies antioxidants and tumors, said the mouse study “provides some really interesting evidence about how antioxidants could help cancer cells in addition to their beneficial effects to normal cells.”
Bergo said his team is now looking at the effect of antioxidants on patients at increased risk of lung cancer.
“We need to understand if this is limited to lung cancer . . . or if the antioxidants can accelerate the growth of other tumors such as malignant melanoma, leukemia, G.I. tumors. We don’t know anything about this. It is possible that antioxidants will increase the growth of some of the cancers, and it is possible that it will prevent others,” Bergo said.
The American Cancer Society’s Eric Jacobs said that the results are “intriguing” but that it is too early to draw any conclusions.
He said doctors recommend that smokers avoid taking beta-carotene supplements, based on the results of the 1994 study, but that the jury is out on other antioxidants.
“The totality of current evidence,” he said, indicates that other antioxidants are “unlikely to have an important effect, either good or bad, on cancer risk in well-nourished individuals.”
Regina Santella, a professor at Columbia University’s Mailman School of Public Health who worked on the large National Institutes of Health-funded study about antioxidants and prostate cancer that was published in 2009, said the mouse study is one of a growing number that question the use of supplements. She said there are also studies about calcium andVitamin D.
“The idea of these magic pills being curative or preventive is turning out to not be true in a lot of cases,” Santella said.