In an alarming study, scientists have found that two commonly used antioxidants - including the popular vitamin E - can fuel the growth of lung cancer in mice rather than curb it.
"The take-home message is that these antioxidants do not decrease the risk of cancer and may even increase risk of some cancers in some populations," cautioned Martin Bergö, a molecular biologist at University of Gothenburg in Sweden and a co-author of the latest study.
Bergö and his colleague, Per Lindahl, a molecular biologist at the University of Gothenburg, conducted experiments in mice that were genetically engineered to develop lung cancer.
They first decided to dose the mice with a compound called N-acetylcysteine (NAC) - another antioxidant.
The control tumours grew three times faster than expected after the NAC dose.
The team decided to dig deeper, and expanded its study to include another common antioxidant - vitamin E, said a report in Nature.
The researchers fed either NAC or vitamin E to the mice, using doses of 5 or 50 times higher than the daily recommended amount for mice.
Human dietary supplements often have 4 to 20 times the recommended daily intake of vitamin E (22.4 EU) for humans.
The results for the two antioxidants were similar. Tumours grew about three times faster than those in animals that did not receive the treatment.
Treated mice also died from their cancers about twice as quickly as untreated mice, said the study published in the journal Science Translational Medicine.
"Our study, however, does not say anything about how antioxidant supplementation affects cancer risk in apparently healthy people," the study added.
According to Lindahl, the work does call for a closer look at the effects of antioxidants in smokers, who are at high risk for lung cancer and may already carry small tumours while outwardly seeming healthy.
He is also concerned about people with a common lung ailment called chronic obstructive pulmonary disease, who are sometimes treated with NAC to reduce mucus production.