Chow Line: A little zinc goes a long way (for 10/1/06)

Why do we need zinc?

Zinc does quite a lot, actually. It's found in almost every cell in the body. It's responsible for activating about 100 enzymes that do a wide variety of essential tasks, such as helping wounds heal and supporting a healthy immune system.

Adult men should get 11 milligrams of zinc a day; women need 8. Zinc is in a wide variety of foods, and eating a healthful, balanced diet should provide you with enough. For example, a 3-ounce hamburger has 5 milligrams of zinc, while 3 ounces of chicken thigh meat has about 2 milligrams and chicken breast has about 1 milligram. Zinc is also found in moderate amounts in pork, lamb, beans, barley, fortified breakfast cereals, crab, whole grains, nuts, eggs and dairy products. Oysters contain the most zinc by far, with 75 milligrams per 3-ounce serving.

Some recent research provides some insight into how zinc works in the body. For example, a study published in the May 2005 issue of the American Journal of Clinical Nutrition examined how a low-zinc diet affects the heart and the role of an enzyme called carbonic anhydrase during exercise. The enzyme helps move carbon dioxide to the lungs, where it is exhaled.

In the study, 14 men in their 20s and 30s were fed a diet either low or normal in zinc for nine weeks, then switched to the other diet after a six-week break. They were tested during workouts in both phases. When on the low-zinc diet, they appeared to work harder during exercise and tended to stop exercising earlier than when on the diet with normal zinc levels. Researchers said when zinc stores were low, the hearts had to work harder to remove carbon dioxide during exercise.

A much larger, seven-year study reported by the National Institutes of Health in 2001 indicates that large supplements of zinc may help slow the progression of age-related macular degeneration (AMD), a leading cause of blindness. The study involved nearly 5,000 people ages 55 to 80 who were given either zinc alone, antioxidants alone, zinc and antioxidants, or a placebo.

Researchers found no effects on participants who began the study with no signs of AMD. But for those who already had intermediate AMD in one or both eyes, or those with advanced AMD in one eye already, the combination of zinc and antioxidants appeared to significantly reduce the chance of additional vision loss. Zinc alone and antioxidants alone also reduced the risk, but not as much as the combination.

For a complete list of the amount of zinc in foods, go to the National Nutrient Database at http://www.nal.usda.gov/fnic/foodcomp/search/ and click on "Nutrient Lists."

Chow Line is a service of Ohio State University Extension and the Ohio Agricultural Research and Development Center. Send questions to Chow Line, c/o Martha Filipic, 2021 Coffey Road, Columbus, OH 43210-1044, or filipic.3@cfaes.osu.edu.

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This column was reviewed by Sharron Coplin, registered dietitian and nutrition associate for Ohio State University Extension and the Department of Human Nutrition in the College of Education and Human Ecology.

To receive a PDF file of Chow Line via e-mail, contact Martha Filipic at filipic.3@cfaes.osu.edu.