Cells have a natural defense € superoxide dismutase (SOD), a special class of antioxidant that neutralizes the chemicals and prevents them from harming cells. The antioxidant theory of aging states that some of the oxygen molecules used by the body become negatively charged, making them reactive.

But in the February PLoS Genetics, Luciano Hekimi and Jeremy. Companies have started putting antiox i dants in goods as different as face creams and soda, claiming that they clean out cells, prevent cancer and even stave off death. According to the theory, proposed in 1956 by Denham Harman, now emeritus professor of medicine at the University of Nebraska, when the body gets older, SODs become less efficient at preventing oxidative stress.

As a result, they compromise health and age the body by damaging cell structures, proteins and DNA. When the SOD dean is knocked out in mice, flies or yeast, the organisms develop cancers and have shorter life spans. Over the past 50 years this widely accepted theory has held up in studies. But a recent study suggests that when it comes to living longer, those antioxidants may not be the answer.

The idea is to prevent unstable oxygen molecules, which are normal by-products of metabolism, from damaging cells.