Zinc for Performance
By Judy McBride

Peak athletic performance depends on adequate zinc as well as iron and copper, according to a new study from the Agricultural Research Service, USDA's chief scientific agency.

While most people don't have to worry, those who avoid beef and load up on carbohydrates may fall short in zinc. Beef is the major source of this essential trace element in the U.S. diet. Wrestlers, gymnasts and ballerinas who eat sparingly to maintain a low body weight may also be at risk of not getting enough zinc.

With these athletes in mind, ARS physiologist Henry C. Lukaski studied the effects of a low-zinc diet on 12 athletic men in their twenties. Based at the Grand Forks, N. D., Human Nutrition Research Center, Lukaski wanted to fill in the limited data on low-zinc intake.

He focused on a zinc-containing enzyme--carbonic anhydrase--in red blood cells. The enzyme helps red blood cells pick up carbon dioxide and drop it off in the lungs to be exhaled. This exchange helps maintain the chemical environment muscle cells need to contract and produce energy. If the exchange is sluggish, the athlete pays the price in performance.

For nine weeks each, the men ate a diet containing 18 milligrams of zinc per day--slightly more than the recommended amount--and another containing only 3 mg/day--one fifth of the recommendation.

After the low-zinc diet, the men had significant drops in peak oxygen uptake and peak carbon dioxide output as they cycled all-out on an ergometer. Their respiratory exchange ratios also dropped, indicating energy production during peak exercise was not up to snuff.

The low-zinc diet also depressed these measurements while the men cycled at 75 percent of peak capacity. The activity of the carbonic anhydrase enzyme also was lower after the low-zinc diet.

The article concluded that the recommended 12-15 mg/day is adequate for peak performance. However researchers caution the intake of high levels of zinc. Supplementing with several times the recommended level can cause health risks.