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United States Department of Agriculture

Agricultural Research Service

A little Zinc is good for you, but a lot is not!
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Philip G. Reeves

Many times we may think that if a little is good for you, more would be better. When it comes to nutrition, more is not necessarily better. Many different nutrients interact with each other in our diet and in our bodies where one might interfere with the utilization of the other. Dietary trace elements are good examples of possible harmful interactions.

Zinc, for example, is one of those nutrients that is absolutely required for health and well-being; however, its intake needs to be properly balanced. The Recommended Dietary Allowance (RDA) for zinc is 15 milligrams/day for men and 12 for women. Because zinc competes with copper for absorption sites in the intestine, too much zinc can lead to signs of copper deficiency.

It was shown by Dr. Leslie Klevay at the Grand Forks Human Nutrition Research Laboratory that copper is one of the sparsest of the trace element nutrients in our diet. A significant number of diets of individuals surveyed contained less than the RDA for copper.

Adding more zinc to our diet could cause us to get even less copper into our bodies. Over time, this could lead to signs of low copper status, which include low blood copper, high serum cholesterol, abnormal heart rhythm, and a lower capacity to subdue oxidizers that can damage delicate cellular machinery, including DNA.

It is easy to get too much zinc in our diet, especially if we take certain dietary supplements. For example, many of the mineral supplements sold in the marketplace today contain 50 to 100 mg of zinc per tablet. This is 3 to 8 times the recommend intake.

A study at the Nutrition Center conducted by Drs. David Milne and Cindy Davis, showed that women volunteers fed 53 mg of zinc per day in an otherwise normal diet with 1 mg of copper, or about the average copper intake of most women, began to develop some signs of low copper status after about 90 days.

Zinc also can affect the status of other trace elements. In the same study described above, 53 mg of zinc in the diet for 90 days lowered both the hemoglobin concentration and the ability of the blood to bind iron. This suggests that women who consume high zinc for a long period could develop deficiencies of both copper and iron.

As a results of these studies we advise against taking vitamin and mineral supplements that contain a lot of zinc. However, If you prefer to take a vitamin/mineral supplement once a day, it should contain no more than 12 to 15 mg of zinc or 100% of the RDA for women and men, respectively.

Without resorting to supplements, a well balanced diet composed of a variety of foods will supply you with your needed zinc without it becoming too much. Rich sources of zinc are red meat, nuts and seeds such as sunflower kernels, whole grains, and shell fish such as oysters.

You also can enrich your diet with copper by eating liver, oysters, potatoes with skins, beans and lentils, dark chocolate, mushrooms, and nuts and seeds, especially sunflower kernels.


Last Modified: 10/23/2006
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