Zinc, a mineral essential to human health, may help protect cells against oxidative damage. A preliminary study by Agricultural Research Service scientists has pinpointed the mineral's little-known role as an antioxidant.

Janet C. King and Leslie R. Woodhouse at the ARS Western Human Nutrition Research Center, Davis, Calif., and Barbara Sutherland, now with the University of California, Davis, conducted the study, along with colleagues from the University of California, Berkeley.

Zinc may safeguard red blood cell membranes against oxidative effects of other minerals such as copper or iron. Cell membranes keep cell contents in place and selectively allow salts and other compounds to flow in and out.

The findings suggest that cell membrane health may be an early, accurate indicator of an individual's zinc needs. In addition, the findings emphasize the importance of consistently consuming enough zinc from such foods as beans, whole grains, shellfish, red meat or dark-meat poultry.

The researchers worked with eight healthy men, aged 27 to 47, who volunteered for the 20-week experiment. The foods that the volunteers ate provided only 4.6 milligrams of zinc, the amount recommended by the United Nations' World Health Organization. For the first five and last five weeks of the study, they also took gelatin capsules that provided, by day's end, an additional 9.1 milligrams of zinc. For the middle 10 weeks of the experiment, the capsules were replaced with placebos, meaning the only zinc provided during that time was the 4.6 milligrams from the food.

Volunteers' red blood cell membranes were significantly more fragile when measured after the 10-week, low-zinc stint. This cell membrane change occurred in the absence of standard indicators of zinc deficiency, according to the researchers. They used several different laboratory procedures, including one known as an osmotic fragility test, to assess membrane strength.

Woodhouse summarized the research at a recent conference of the International Society for Trace Element Research in Humans, held in Quebec City, Canada.