Some 400 million people worldwide may be susceptible to oxidative stress from foods with high oxidant levels such as fava beans, and from smoking, a severe oxidative stress. Upon eating fava beans or even inhaling fava pollen, they can develop potentially fatal hemolytic anemia, called "favism." Those afflicted develop jaundice and excrete blood in their urine. Nearly 10 percent of those with such symptoms die.

Video: Favism, a deficiency of the enzyme G6PD, results from a genetic adaptation to fight malaria.

Scientists have pinned the problem to various genetic variations, several of which are common among southern Europeans, that appear to have come about to help the body fight off malaria infection, but which also make people react severely to oxidants such as those in fava beans.

The genetic mutations reduce the activity of the enzyme glucose-6-phosphate 1-dehydrogenase (G6PD), which is involved in regenerating glutathione, an antioxidant.

"The mutations lower glutathione levels so that we can survive but the malarial parasite cannot survive," Ames said. "So it makes us more resistant to malaria, but at the price of being on the borderline of antioxidant defenses."

A meal of fava beans dumps the powerful oxidants vicine and divicine into the body, overwhelming the antioxidants in the blood and producing anemia.

In searching the scientific literature, Ames and Elson-Schwab found that one common mutation in the enzyme affects the site where it binds with NADP (nicotinamide adenine dinucleotide phosphate), a cofactor made from niacin, or vitamin B-3. Those with favism may be able to supplement their diet with niacin to avoid oxidative stress and hemolytic anemia that can result from fava beans, smoking, and some drugs in areas where malaria has been eliminated.

— By Robert Sanders, Media Relations

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