Antioxidants may cause cancer to spread faster, says a new study

Mice that were given antioxidants developed additional and more aggressive tumours. Experiments on human lung cancer cells confirmed the results.

Found in many nutritional supplements, antioxidants are widely marketed as a means of preventing cancer.

The follow-up studies have now found that antioxidants double the rate of metastasis in malignant melanoma, the most perilous type of skin cancer.

"As opposed to the lung cancer studies, the primary melanoma tumour was not affected," Bergo said.

"But the antioxidant boosted the ability of the tumour cells to metastasise, 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," he said

Experiments on cell cultures from patients with malignant melanoma confirmed the new results, researchers said.

"We have demonstrated that antioxidants promote the progression of cancer in at least two different ways," Bergo said.

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 tumour once it has developed.

Taking nutritional supplements containing antioxidants may unintentionally hasten the progression of a small tumour or premalignant lesion, neither of which is possible to detect, researchers said.

"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," Bergo added.

The study was published in the journal Science Translational Medicine.