NUTRITION NOTES: Everybody’s Science
By Sandy Miller Hays, Agricultural Research Service

Think Zinc

Zinc is an essential mineral that has many functions in the human body. You can get your zinc from many foods, such as oysters (6 medium), 76.28 mg; beef, top sirloin, broiled (3 oz.), 4.97 mg; and peanuts, dry roasted (1 oz.), 0.94 mg.

We've all read a lot lately about the problems caused by poor childhood nutrition and the epidemic of childhood obesity in this country. If you're a parent who wants to make sure your child is getting the best in nutrition, here's another step you can take to help your child: think zinc. According to studies by scientists with the Agricultural Research Service, adequate levels of zinc can help your child learn and reason better. And zinc isn't that hard to come by in the diet; you can get it from eating nuts, popcorn, beans, whole-wheat products (such as crackers and bread), cheddar cheese, poultry, lamb, pork, oysters and liver. Probably the most common source of zinc in the American diet is red meat. In one study, 372 Chinese schoolchildren aged 6 to 9 years were divided into three groups. One group took a 20-milligram zinc supplement daily for 10 weeks.

A second group took the zinc supplement plus a micronutrient supplement containing all essential vitamins and minerals except for zinc and four other minerals known to interfere with the body's absorption of zinc. A third group received only the micronutrient supplement.

Before and after the supplement period, each child took a series of tests to measure attention, perception, memory, reasoning and the motor and spatial skills that are necessary for a child to do well in school. The results: The children who got the zinc supplement, or zinc plus the micronutrients, had the most improved performance, especially in perception, memory and reasoning skills.
How much zinc is enough? The Recommended Daily Allowance (RDA) of zinc for grade-school- age children is 10 milligrams daily. But about 10 percent of American girls in this age group don't hit that mark, and about 6 percent of boys; in fact, they typically get less than half of the RDA.

In case you've never thought much about zinc, here's food for thought: Zinc probably affects every general function in our bodies. For one thing, it's a critical part of the mechanism that turns on and off our genes. We're talking about genes that tell our bodies to make proteins, enzymes and hormones – in other words, the substances that make our bodies "work." Also, zinc has an important role in many of the enzymes that we need in order to have healthy skin and proper functioning of our immune, nervous and digestive systems; it helps our bodies guard against infections and repair wounds.

If you're thinking at this point, "Hey, it sounds like zinc isn't just for kids", you're absolutely right. You've probably heard of antioxidants – substances that help protect your body's essential parts (such as cell walls) against oxidative damage that occurs naturally over time.

Studies indicate that zinc may help protect your red blood cell membranes against oxidative effects of other minerals such as copper and iron.
If you're an adult female, you may be taking extra calcium, either through supplements or dairy consumption, to help fend off osteoporosis. If so, you need to be aware that some studies indicate that extra calcium can block zinc absorption. (If you were surprised to find out that as much as 10 percent of grade-school-age girls don't get enough zinc, hold onto your hat for this one: Survey data indicate that about 50 percent of U.S. women get less than two-thirds of their RDA for zinc, which is 12 milligrams.) And to make matters worse, the amount of zinc you can absorb from your diet decreases as you age.

In a ARS-funded study at the USDA Jean Mayer Human Nutrition Research Center on Aging, at Boston, Mass., 18 relatively healthy women past menopause boosted their calcium intake to 1,356 milligrams daily, which is a little higher than the 1,200 mg now recommended for people over age 50. When they did that, their zinc absorption dropped by about 2 milligrams, and that was regardless of whether they got the extra calcium from milk or from a supplement.

Finally, there's one other group that needs to keep a close eye on zinc intake: vegetarians. You may have noticed that many of the good sources of zinc listed above are meats. In fact, vegetarian diets in the U.S. typically contain anywhere from 10 to 30 percent less zinc than non-vegetarian diets.

They also contain a lot of fiber and phytic acid, which tend to tie up minerals and make them less available for absorption. Still, the scientists say if you're a vegetarian who at least includes milk and eggs in your diet, you can probably meet your zinc needs by eating plenty of whole grains and legumes.

So if you're looking for something simple and good to do for your body this year: think zinc!

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