Antioxidant Supplements Fuel Lung Cancer in Mice

Swedish researchers have found that giving antioxidant supplements to mice with small lung tumors caused the tumors to grow more quickly, become more invasive, and kill the mice faster than tumors in mice not given the supplements. The researchers say the findings point to a need for more research to determine the value and safety of these supplements in people.

Antioxidants are made by plants and are found in fruits, vegetables, beans, and grains. Because eating a wide variety of plant-based foods has been shown to provide many health benefits including lowering cancer risk, some people speculate that taking antioxidant supplements can help prevent many health problems. However, scientific evidence has not been able to show that taking supplements is as good for long-term health as eating the foods they come from.

Some of the better-known antioxidants include beta carotene, ascorbic acid (vitamin C), and vitamin E. Most studies involving antioxidants have disappointed researchers hoping to find a disease-fighting powerhouse. For example, studies have shown that taking large amounts of vitamin E not only does not prevent prostate cancer, it may actually increase the risk. Other studies found a link between beta carotene and lung cancer.

Colleen Doyle, MS, RD, Director of Nutrition and Physical Activity at the American Cancer Society, says a distinction has to be made between antioxidant supplements and the foods they come from. “A number of trials which gave high-dose beta carotene supplements to people at high risk for lung cancer were actually stopped early because those people were developing lung cancer at higher rates,” she said. “Foods rich in beta carotene may be helpful in reducing the risk of lung cancer, but much of the research on beta carotene supplements suggests quite the opposite, at least for subgroups of the population.”

In the Swedish study, researchers compared the effects on mice of a normal diet to a diet with either additional vitamin E or a relatively low doses of acetylcysteine. Acetylcysteine is an antioxidant that is sometimes prescribed to people with chronic obstructive pulmonary disease (COPD) to thin out their mucous and help them breathe better. The mice were exposed to a virus that causes lung tumors to develop. More and worse tumors developed in the mice exposed to the antioxidant supplements than in the mice fed a normal diet.

“The take-home message from these trials is that antioxidants do not protect against cancer,” said study author Martin O. Bergö, PhD. “It may even increase the risk of some forms of cancer.”

The study was published January 29, 2014 in Science Translational Medicine.

Antioxidants, lung cancer, and people

In addition to studying antioxidants in mice, the researchers also tested antioxidants on human lung cancer cells in the laboratory. They found similar results: The antioxidants increased the growth of human lung cancer cells. According to Bergö, this suggests the findings might apply to people with lung cancer.

“If you have lung cancer or an increased risk of developing lung cancer, for example if you are a smoker or if you have a lung disorder like COPD, taking extract antioxidants might be harmful. If you have a small, undiagnosed lung tumor, it could speed up the growth of the tumor.”

Bergö emphasized that recommendations for the general population cannot be made based on the study, which did not test antioxidant supplements in people. He said the findings raise questions about the safety of antioxidant supplements and demonstrate the need for more research. He said further study is especially needed to determine whether acetylcysteine is causing an increased risk of lung cancer in people with COPD.

According to Doyle, while there is not good evidence that antioxidant supplements are helpful in reducing cancer risk, and in some cases may be harmful, it’s also important to consider the fact that many people who are being treated for a chronic disease, such as cancer, are also taking supplements. Doyle said this is an issue patients should discuss with their health care team. “Some types of supplements may interfere with or counteract the treatment that is being given, so patients should absolutely discuss this issue with their doctors, and make an informed decision on whether a particular supplement – first and foremost – is safe for them to take.”

Antioxidants in food

According to Bergö, people should not stop eating fruits, vegetables, beans, and whole grains because of the study. “You’d have to eat a lot of antioxidant-rich foods to get up to the levels of the supplements,” he said. “Nothing in the research points a finger at antioxidant-rich foods.”

In fact, the American Cancer Society recommends a primarily plant-based diet that includes at least 2½ cups of vegetables and fruits each day and whole-grain rather than refined-grain foods. According to Doyle, this recommendation is based on many different studies showing a positive benefit in reducing the risk of a variety of different types of cancer. ”Focus on eating colorful fruits, vegetables and whole grains each day. It’s likely that the synergy of all those nutrients working together is what is helpful in reducing cancer risk, and you just can’t get that out of supplement.“

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master's-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Antioxidants Accelerate Lung Cancer Progression in Mice.  Published January 29, 2014 in Science Translational Medicine. First author Volkan I. Sayin, University of Gothenburg, Gothenburg, Sweden.

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