The rise in popularity of consuming antioxidant-rich foods has led several companies to encourage people to take extra doses through advertised supermarket labels seen on items such as frozen fruits and green tea. While adding antioxidant supplements to a daily diet is meant to strengthen the ability to fight infection and disease, it can also backfire and accelerate the growth of cancerous tumors. According to a recent study published in Science Translational Medicine, taking high doses of antioxidants such as vitamin E and acetylcysteine may speed up the progression of lung cancer in smokers and other high-risk patients.

Antioxidants such as beta-carotene, lutein, lycopene, selenium, vitamins A, C, and E are found in many foods and are also available as dietary supplements. They are meant to protect the body from disease by preventing cell damage caused by molecules known as free radicals, says the Harvard School of Public Health. These radicals can damage almost anything inside the cell including DNA, which can lead to cancer. However, high-dose supplements of antioxidants may be linked to health risks and could interact with some medicines. The protection they initially intend to provide can backfire in those who already have cancerous or precancerous cells.

A team of researchers at the University of Gothenburg, Sweden, sought to monitor the effects a diet with antioxidants supplements had on a group of mice with early lung cancer. Small, normal, and higher doses of vitamin E and antioxidant supplement acetylcysteine were administered to the rodents with a presence of the disease. Acetylcysteine, a synthetic antioxidant drug, is normally prescribed in inhaled form to patients with chronic obstructive pulmonary disease (COPD), which is a lung disease that is often triggered by smoking. Although it is water-soluble, whereas vitamin E is oil-based, they both have common antioxidant properties.

The findings revealed normal doses of vitamin E and smaller doses of acetylcysteine increased the growth of tumors in mice with early lung cancer. The antioxidants caused the mice to die twice as fast and was dose-dependent. For example, if the researchers administered a small dose, the tumors grew little, but if they gave them a high dose, the tumors grew a lot. The antioxidants harmed rather than helped the cancer patients by accelerating the progression of the disease.

Typically, when the body detects cellular DNA damage that can lead to cancer, it release a tumor-suppressing protein — p53. In the rodent study, the antioxidants not only destroyed free radicals, but also suppressed the release of p53. "By reducing the DNA damage, the antioxidant actually helps the cancer cells escape detection," said Per Lindahl, co-author of the study and a professor of biochemistry and cell biology at the University of Gothenburg, HealthDay reported.

The Swedish researchers found the results of this study particularly concerning because the antioxidant supplement — acetylcysteine — is commonly used to improve breathing in patients with COPD. Most patients with COPD are current or former smokers. They stress people carrying small undiagnosed tumors in their lungs should avoid taking extra antioxidants. "If you have lung cancer, or if you have an increased risk of developing lung cancer, then taking extra antioxidants may be harmful and it could speed up the growth of a tumor," said Dr. Martin Bergo, senior author of the study.

The relationship between extra doses of antioxidants and its role in cancer progression have been observed in earlier studies. In a similar study published in The New England Journal of Medicine, unexpectedly, researchers found a higher incident of lung cancer among men who received beta-carotene compared to those who did not. These men were smokers who took daily supplements of this antioxidant for five to eight years that were found more likely to die from lung cancer or heart disease.

These studies provide laboratory evidence that some of the effects of antioxidants backfire. The human body’s ability to create its own antioxidants and adding antioxidant supplements could defeat the body’s ability to fight cancer and disease. The Swedish researchers advise healthy people should not limit themselves from taking extra antioxidants because they need to understand if it is limited to lung cancer or if they can accelerate the growth of other tumors such as malignant melanoma, leukemia, G.I. tumors. “It is possible that antioxidants will increase the growth of some of the cancers, and it is possible that it will prevent others,” said Bergo, The Washington Post reported.

Whether antioxidants have a good or bad effect on cancer risk in healthy individuals remains to be known. Scientific data has encouraged and also erred on the side of caution when it comes to antioxidant supplements. The belief that antioxidants may “cure” or “prevent” cancer and other diseases is being put into question in a lot of studies.


Bergo MO, Ibrahim MX, Larsson E, Lindahl P, Nilsson JA, and Sayin VI. Antioxidants Accelerate Lung Cancer Progression in Mice. Sci Transl Med. 2014.

The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. N Engl J Med. 1994.