Antioxidants could increase the risk of cancer spreading around the body

The so-called disease-fighting compounds could actually double the rate at which malignant melanoma spreads

Taking too many antioxidant-containing health supplements can increase the risk of certain types of cancer. ( (Photo by Mario Tama/Getty Images))

Compounds popularly thought of as protecting the body from cancer could actually increase the risk of the disease, according to a new study.

Antioxidants are taken by millions in health supplements such as Vitamin E and beta-carotene. The disease-busting molecules are supposed to keep your cells healthy but could actually double the rate at which skin cancer spreads when taken in the kind of high doses found in supplements.

The study did not look at the impact of antioxidants that are found in naturally occurring so-called superfoods such as blueberries, raspberries and nuts. Supplements normally contain significantly higher levels of anti-oxidants and there is no suggestion that eating such foods would have the same potential impact as taking supplements containing much high doses.

The study, which was carried out by scientists in Sweden, found that mice that had been given doses of antioxidants similar to those found in human supplements developed twice as many tumours in their lymph nodes –a sign of ‘metastasis’ or the spread of cancer to other parts of the body.

The scientist leading the study, Professor Martin Bergö from the University of Gothenburg, said in a report published in Science Translational Medicine: “… 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 tumour is not dangerous per se and is usually removed."

Conventional wisdom has been that antioxidants help the body by fighting cancer-causing free radicals. However experts now believe that high levels of antioxidants actually protect cancer cells themselves.

Experiments involving cells from patients with skin cancer confirmed that the same results occur in humans.

Professor Bergö warned against the use of supplements containing antioxidants, saying: “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."

Earlier studies have also hinted at the harmful effects of large doses of antioxidants. A 1994 trial found that large daily doses of beta-carotene increased the risk of lung cancer in smokers by 18 per cent.

And in 1996 researchers found that high-dose beta-carotene and retinol – another form of vitamin A – increased lung cancer risk in smokers by 28 per cent.

Most recently a 2011 trial of 35,500 men over 50 found that large doses of vitamin E increased the risk of prostate cancer by 17 per cent.

The Swedish team have previously show that antioxidants also hasten the progression of lung cancer. They are currently researching whether skin lotions containing antioxidants also affect the spread of melanoma.

Professor Bergö has stressed the need for further research: “other forms of cancer and types of antioxidants need to be considered if we want to make a fully informed assessment of the role that free radicals and antioxidants play in the process of cancer progression."