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Zinc
Zinc has been identified as a cofactor in at least forty different enzyme systems, covering every major physiological function dependent upon enzymes. Without adequate zinc, for example, carbon dioxide exchange in the cells could not take place at a fast enough rate to sustain life.
Zinc also appears to have a major role in the synthesis of nucleic acids, including RNA and DNA, and in protein synthesis. It is necessary for cell growth and the formation of connective tissue, both of which processes depend heavily on nucleic acids and protein synthesis.
Zinc also appears to have a protective role in the cells and cell membranes, perhaps by exerting an antioxidant effect. Metabolism of other minerals, such as copper, magnesium, manganese, and selenium, have also been found responsive to changes in zinc balance in the body. In this respect, zinc may perform some regulatory functions.
Since zinc is necessary for cell growth, any tissue which depends on relatively rapid cell proliferation will suffer the effects of a deficiency first and most severely. So a zinc deficiency can result in delayed healing of wounds, deformities in offspring born to deficient mothers, impaired development of bones, muscle, and nervous system, delayed sexual maturation, testicular atrophy and dysfunction, loss of hair, deformed nails, skin lesions, infertility, impaired immune response, reduced salivation, atrophy of the thymus gland, and reduced absorption of nutrients.
Zinc deficiency in children will manifest itself in loss of appetite, loss of the sense of taste and smell, impaired growth, dermatitis, diarrhea, hair fall, and depression. Acrodermatitis enteropathica is a fatal disease now known to be due to an inherited defect which causes impaired absorption of zinc. The resultant severe deficiency causes diarrhea, loss of hair, severe dermatitis, lesions in the eyes, psychological disturbances, and greatly increased susceptibility to infections. The disease usually appears in early infancy, although breastfed babies with the disease are protected until they are weaned (breast milk contains zinc which is absorbed extraordinarily efficiently). A child with acrodermatitis enteropathica fails to thrive and is beset with numerous infections. Victims rarely survive childhood. Women with this severe zinc deficiency who have survived into the childbearing years have given birth to severely deformed infants.
In adults, zinc deficiency results in the same symptoms as in children, with some differences owing to advanced maturity. For example, whereas young males and females will suffer retarded sexual development, adults will suffer infertility and impaired sexual function. Skin lesions, impaired wound healing, loss of appetite, taste, and smell, hair fall, and increased susceptibility to infection affect all ages in a zinc deficiency.
There are many factors which can reduce the body's zinc status and contribute to a deficiency. Most truly severe deficiencies of zinc are thought to be the result of genetic defects or diseases interfering with zinc metabolism. Acrodermatitis enteropathica is an example. Several diseases also cause low blood levels of zinc, perhaps because of increased requirements. These include alcoholism, atherosclerosis, chronic cutaneous ulcers, cirrhosis, Down's Syndrome, dwarfism, lung cancer, leukemia, myocardial infarction, pulmonary infection, tuberculosis, diabetes, hepatitis, uremia, burns, bacterial and viral infections, acute inflammatory diseases, malabsorption syndromes, steatorrhea, blood loss, schizophrenia, and thyrotoxicosis.
Other factors can affect zinc levels besides disease and deficient food. Zinc absorption varies from twenty to eighty percent, but is normally only twenty to thirty percent. Increased absorption occurs during a deficiency, as the body tries to allow more zinc into the blood. Content of the diet, irrespective of the amount of zinc, can also have an effect. High-fiber diets have been shown to decrease zinc absorption. Apparently, phytates (phosphorus compounds) in cereal grains can inhibit the absorption of zinc. For this reason, zinc from animal foods (which-are low in fiber and phytates) contain zinc which is more "available." Just how much fiber in cereals and vegetables affects zinc absorption is not precisely known. Some studies have even shown that there is no effect. In any case, the fact that fiber may decrease zinc absorption is no reason to cut down ,on fiber, since fiber is every bit as important to our health as zinc, if for different reasons. Lemon juice has also been found to impair zinc absorption. And high protein diets may increase zinc requirements.
Several medications can cause zinc deficiency, too, including chelating agents, diuretics, corticosteriods, and oral contraceptives.
Cadmium toxicity is prevented by zinc. Cadmium, however, also uses up zinc in the process. So a high-cadmium diet will increase zinc requirements. Unfortunately, food processing and refinement remove zinc, but leave in or increase the cadmium in foods. So a diet of processed foods, in itself, can increase your zinc requirements.
Zinc absorption is known to respond to the body's needs. The body actually gets two chances to absorb zinc with every meal, once from the foods you've eaten (assuming they contain some zinc) and once again from the digestive juices secreted by the pancreas. As a matter of fact, there are substances in digestive juices which greatly enhance zinc absorption. Furthermore, the intestines are not "passive" when it comes to absorbing zinc. They can increase or decrease the efficiency of zinc absorption according to the body's needs.
Where is Zinc found?
The best natural sources of zinc are sea foods (especially oysters and herring), liver, meats, milk, eggs, nuts, legumes, and brewer's yeast. For infants, breast milk is the best source of zinc, since the zinc in breast milk is absorbed so well that it has been used to supply zinc in cases of malabsorption and impaired utilization.
Zinc is also available in supplemental form in various compounds (zinc sulfate, zinc gluconate, etc.) Zinc sulfate is the most common form used in medical experiments, despite the fact that it is a stomach irritant. Zinc acetate is also used and appears to be less troublesome. If zinc sulfate is used, the supplement can be taken with meals to reduce the chances of stomach upset.
Who is likely to be deficient?
Low-income pregnant women and pregnant teenagers are at risk for marginal zinc deficiencies. Supplementing with 25 to 30 mg per day improves pregnancy outcome in these groups.
The average diet frequently provides less than the recommended daily allowance for zinc. A low-dose supplement (15 mg per day) can fill in dietary gaps. Zinc deficiencies are more common in alcoholics and individuals with sickle cell anemia, malabsorption problems, and chronic kidney disease.
How much Zinc to take?
Moderate intake of zinc, 15 to 25 mg, is adequate to prevent deficiencies. Higher levels (up to 50 mg taken 3 times per day) are reserved for treating certain health conditions, under the supervision of a nutritionally oriented doctor. For the alleviation of cold symptoms, lozenges providing 15 to 25 mg of zinc in the form zinc gluconate are generally used frequently throughout the day.
Side Effects
Zinc intake in excess of 300 mg per day has been reported to impair immune function. Some people report that zinc lozenges lead to stomachache, nausea, mouth irritation, and a bad taste. In topical form, zinc has no known side effects when used as recommended.
Preliminary research had suggested that people with Alzheimer's disease should avoid zinc supplements. More recently, preliminary evidence in four patients actually showed improved mental function with zinc supplementation. In a convincing review of the zinc/ Alzheimer's disease research, perhaps the most respected zinc researcher in the world concluded that zinc does not cause or exacerbate Alzheimer's disease symptoms.
Zinc inhibits copper absorption, which can lead to anemia and lower levels of HDL cholesterol (the "good" cholesterol). Copper intake should be increased if zinc supplementation continues for more than a few days (except for individuals with Wilson's disease). Many zinc supplements, to prevent copper inhibition, include copper in the formulation.
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