More than 50 years ago, in 1934, zinc essentiality was first suggested. Not until the early 1960s, however, was it known that low intake or low body stores of zinc can cause deficiency symptoms. In recent years, since the discovery that this mineral is becoming less available in our soil and thus in our food chain, zinc has been given more attention, and increased research has produced much new information. We now know that zinc is needed in probably more than 100 enzymes and is probably involved in more body functions than any other mineral. It is important in normal growth and development, the maintenance of body tissues, sexual function, the immune system, and detoxification of chemicals and metabolic irritants. Carbohydrate metabolism is influenced by zinc, and zinc is needed in the synthesis of DNA, which aids our body's healing process. Zinc is often helpful in reducing healing time after surgery or burns, in many male prostate problems, in skin diseases, and in many other difficulties.

Zinc is found in the body in small amounts, only about 2-2.5 grams total. Of the trace minerals, it is second in concentration to iron, with 33 ppm to iron's 60 ppm. (Although fluoride is found at 37 ppm in the average human body, it is still questionable whether it is essential. This 37 ppm is also a result of the use of fluoridated water, vitamins, and stannous fluoride toothpaste.) Though zinc is the twenty-fifth most abundant element in the earth's crust, measuring about 0.01 percent, it is water soluble both in the soil and in food. Rains can wash zinc (as well as iodine, sulfur, and selenium) from our farming soils, as can modern agricultural techniques. When we cook food, much of the zinc may go into the water, as do other minerals and vitamins, so the cooking liquids, especially from vegetables, should be consumed as well. More importantly, when foods are processed, as in the refining of grains, much of the zinc is lost, along with manganese, chromium, molybdenum, and B vitamins. Usually, only iron and sometimes vitamins B1 and B2 are added back in "enriched" foods (and this iron isn't even in the easily usable form). Adding zinc, manganese, chromium, and more B vitamins such as B6, would be much better and help us avoid common deficiencies.

Zinc absorption may vary from about 20-40 percent of ingested zinc, depending mainly on body needs and stomach acid concentrations. Like iron, zinc from animal foods where it is bound with proteins has been shown to be better absorbed. When bound with the phytates or oxalates found in grains and vegetables, less zinc is absorbed. Calcium, phosphorus, copper, iron, lead, and cadmium all compete with zinc for absoprtion. Milk and eggs reduce zinc absorption. Fiber foods, bran, and phytates, found mainly in the outer covering of grains, may also inhibit zinc absorption. Phytic acid may combine with the zinc in the upper intestine before this mineral can be absorbed.

The zinc-cadmium relationship is interesting. Cadmium is considered a potentially toxic heavy metal. When it contaminates our food, it is found in the center of grain; zinc is found mainly in the grain covering. So eating whole grains, which have a higher amount of zinc than of cadmium, will reduce any possible absorption of cadmium. With refining of grains into flour, the zinc-cadmium ratio is decreased, and cadmium is more likely to be absorbed and cause problems.

In the human body, the 2.5 grams of zinc are stored in a variety of tissues. It is most concentrated in the prostate and semen, which suggests zinc's tie to male sexual function (impotence can be related to low zinc). The next most concentrated tissues are the retina of the eye, heart, spleen, lungs, brain, and adrenal glands. The skin contains a high amount of zinc, but it is less concentrated than in the organ tissues. Nails, hair, and teeth also have some zinc, and this mineral is important to those tissues as well.

Zinc is eliminated through the gastrointestinal tract in the feces. Some is also eliminated in the urine; alcohol use increases urinary losses of zinc. Zinc is also lost in the sweat, possibly as much as 2-3 mg. in a day. Stress, burns, surgery, and weight loss all seem to increase body losses of zinc.

In evaluating body zinc status, plasma or serum zinc levels may not reflect body stores; however, if they are low, zinc is likely deficient. Low hair levels appear to reflect zinc deficiency, which then should be substantiated through a blood test. High hair zinc levels may also be seen with zinc deficiency, though this is not as correlative as low hair levels. In general, the red blood cell (or white blood cell) measurement of zinc may be most indicative of the body's true status of zinc nutriture.

Sources: Most animal foods contain adequate amounts of zinc. Oysters are particularly high, with more than ten times as much as other sources (they are also high in copper and, possibly, in ocean-polluting chemicals and metals). Zinc is added to animal feeds to increase growth rates, so meat usually contains high amounts. Red meats (beef, lamb, and pork) and liver are fairly high; herring is good, as are egg yolks and milk products (though the zinc in eggs and milk products may not be as available to the body as that found in other sources). Other fish and poultry also contain fair zinc levels. As with iron, the zinc in animal foods seems to be better absorbed than that in the vegetable sources, but one can reduce meat foods and eat whole grains and beans and still obtain adequate zinc. Overall, though, in my experience it is not easy for most people eating a relatively healthy diet to obtain the minimum requirement of 15 mg. daily unless they focus on zinc-containing foods.

Whole grains such as whole wheat, rye, and oats are rich in zinc and are good sources for vegetarians. Even though the mineral from these foods is utilized less well because the fiber and phytates in the grain covering bind some zinc in the gastrointestinal tract, much of the zinc in these foods is still available to the body. Nuts are fairly good sources, with pecans and Brazil nuts the highest. Pumpkin seeds contain zinc and are thought to be helpful to the prostate gland. Ginger root is a good zinc source, as are mustard, chili powder, and black pepper. In general, fruits and vegetables are not good zinc sources, although peas, carrots, beets, and cabbage contain some zinc.

The zinc in grains is found mainly in the germ and bran coverings, so refining them will lower the zinc content. Approximately 80 percent of zinc is lost in making white flour from whole wheat. Since zinc is soluble in water, canning foods or cooking in water can cause zinc losses. Zinc losses have also been prevalent in agricultural soils, and it is therefore less available in foods. Chemical fertilizers also decrease zinc soil levels. Many soils-nearly 30 states in the United States-are deficient in zinc. Water, especially from some wells, contains zinc. Water was a better source when some of the water pipes were galvanized (containing zinc), as were some cooking pots. Now, water pipes are more commonly made of copper, which can become toxic at higher levels.

Functions: Zinc is involved in a multitude of human body functions and is part of many enzyme systems. With regard to metabolism, zinc is part of alcohol dehydrogenase, which helps the liver detoxify alcohols, including ethanol (drinking alcohol), methanol, ethylene glycol, and retinol (vitamin A). Zinc is also thought to help utilize and maintain body levels of vitamin A. Through this action, zinc may help maintain healthy skin cells and thus may be helpful in generating new skin after burns or injury. By helping collagen formation, zinc may also improve wound healing. Zinc aids the skin's oil glands and so may help in acne problems.

Zinc is needed for lactate and malate dehydrogenases, both important in energy production. Zinc is a cofactor for the enzyme alkaline phosphatase, which helps contribute phosphates to bones. Zinc is also part of bone and tooth structure. Zinc is important to male sex organ function and reproductive fluids. It is in high concentration in the prostate gland as well as in the eye, liver, and muscle tissues suggesting its functions in those areas.

Zinc in carboxypeptidase (a digestive enzyme) helps in protein digestion. Zinc is important for synthesis of nucleic acids, both DNA and RNA. In fact, we are finding that zinc has some antioxidant function. As part of superoxide dismutase (SOD), it helps protect cells from free radicals. Through this antioxidant effect, zinc is also helpful in cell membrane structure and function.

Zinc has also been shown to support immune function. Zinc will improve antibody response to vaccines and can improve cell-mediated immunity by helping regulate the function of the white blood cells. A somewhat higher amount of zinc has caused an increase in production of T lymphocytes, important agents in cell-mediated immunity.

Zinc is important to normal insulin activity and seems related to normal taste sensation. Zinc may have an anti-inflammatory function, especially in the joints and artery linings. It may also be involved in brain function, in maintaining acid-alkaline balance through carbonic anhydrase, another zinc-containing enzyme, and in phosphorus metabolism.

More research is needed on this important mineral. As zinc, due to its function in many enzymes, is so important to chemical detoxification and our ability to handle environmental chemicals and toxins, zinc deficiency may be an underlying factor in those people who become environmentally sensitive. This is just one example of where further zinc research may be valuable.

Uses: Just as it has many functions, zinc has a wide variety of clinical uses. Some of these regularly show very positive results; other uses have variable outcomes, and some new therapeutic trials are under way.