Zinc in Health and Nutrition

      Zinc is such a critical element in human health that even a small deficiency is a disaster. Zinc supplementation is a powerful therapeutic tool in managing a long list of illnesses. Zinc, an essential trace mineral, is required for the metabolic activity of 300 of the body's enzymes, and is considered essential for cell division and the synthesis of DNA and protein. These enzymes are involved with the metabolism of protein, carbohydrate, fat and alcohol. Zinc is also critical to tissue growth, wound healing, taste acuity, connective tissue growth and maintenance, immune system function, prostaglandin production, bone mineralization, proper thyroid function, blood clotting, cognitive functions, fetal growth and sperm production.

      Zinc is the number-one nutritional deficiency in U.S. children, according to a Tufts University study. More than 50 percent of poor children and 30 percent of non-poor children, ages 1-5, get less than 70 percent of the Recommended Dietary Allowance of zinc. The study shows that of 16 key nutrients, more children were deficient in zinc than in any other nutrient. Zinc deficiency has been implicated as a factor in:

      Zinc is necessary to maintain normal serum testosterone. Inadequate zinc levels prevent the pituitary gland from releasing luteinizing and follicle stimulating hormones, which stimulate testosterone production.

      Zinc also inhibits the aromatase enzyme that converts testosterone into excess estrogen. The testosterone to estrogen ratio in men declines with aging from a high of about 50:1 to half of that, or even a low of 10:1. Higher estrogen activity results in increasd risk of heart disease, weight gain, and obesity.

      One reason for the progressive weight gain with age is that fat cells contain aromatase. More fat cells mean more estrogen which means more fat deposition.

      This is further aggravated by alcohol consumption, which lowers zinc and increases estrogen, and so magnifies the problem.

      In addition to the impact on hormone levels, zinc also has been proven to help the body produce healthier sperm by increasing sperm count and motility. A USDA study found that semen volume dropped 30 percent when zinc intake was low. Research published in the American Journal of Clinical Nutrition found that male volunteers who consumed low amounts of zinc exhibited decreased semen volumes and serum testosterone concentrations.

      Zinc deficiency has been found to have a severe impact on the male prostate gland. Zinc deficiency predisposes the prostate to infection (prostatis) which may lead to enlargement of the prostate gland (prostatic hypertrophy).

      The significance of zinc in the body's response to infection is well known. Zinc is a component in thymic hormone which controls and facilitates the maturation of lymphocytes. Zinc also plays a role in cell division and DNA replication, thereby aiding in the production of immune system cells.

      Zinc gluconate lozenges taken at the first sign of a cold reduce duration and symptom severity according to a 1992 study. Zinc, an antiviral agent and astringent, is released into the saliva, relieving cough, nasal drainage and congestion. Dr. Michael Macknin told CNN news. "It's the first thing I'm aware of that actually decreased the duration of cold symptoms to this extent." Researchers studied 100 patients who had cold symptoms for less than 24 hours, giving half of the patients a zinc lozenge and the other half a placebo. " ...... there was nearly a 50 percent reduction in the duration of the symptoms of the common cold."

      Zinc is found in the vesicles of the mossy fiber system of the brain's hippocampus. These fibers play a role in enhancing memory and thinking skills.

      University of Texas researchers found that women deficient in zinc had a harder time on standard memory tests.

      USDA scientists found lower cognition in men experimentally deprived of zinc.

      Experiments have shown that accident victims who are given zinc supplements respond with improved cognitive function. Zinc is diverted to the healing tissues following injury or surgery and becomes less available for other essential functions.

      Zinc is essential for healthy skin. Topical zinc preparations (zinc oxide) has been used as an astringent to treat diaper rash, itching and chapped lips and skin. Zinc sulfate in a water based solution has been used for treating acne, cold sores and burns. Remember that zinc sulfate is a salt and can be quite caustic to raw tissue in high or moderate concentrations. Internally, zinc stimulates cell division, healing, proper connective tissue formation, and increases the transport of Vitamin A from the liver to the skin, helping to protect body tissue from damage and repair any damage present.

      Zinc activates areas of the brain that receive and process information from taste and smell sensors. Its importance to appetite was first demonstrated in 1972 when researchers showed taste disorders responded to zinc supplementation.

      Levels of zinc in plasma were found to influence appetite and taste preference. Insufficient zinc has been linked to anorexia, which responds well to zinc replacement treatment.

      Zinc abnormalities also often exist in mood disorder patients. Zinc sulfate, taken as a supplement, appears effective in reducing fatigue, mood swings and changes in appetite.

      It is critical that a pregnant woman satisfy her body's need for zinc. The official RDI for pregnant women is 19 milligrams per day. A report in the October 1992 American Journal of Epidemiology indicated that low zinc intake was associated with approximately a two-fold increase in risk of low birth weight, and low zinc intake earlier in pregnancy was associated with more than a trebling of pre-term delivery.

      Research reported in the British medical journal, The Lancet, September 1992, notes that by the sixth month of lactation even a well-nourished mother may provide less zinc than is necessary for her child. Breastfed babies who received zinc supplements grew significantly in length and weight over those given a placebo.

      As a woman ages, her zinc status may decline for several reasons. Excess estrogen can lower serum zinc levels. Women using estrogen replacement therapy should check to be sure their zinc intake is adequate. A Wayne State study found that nearly 30 percent of a large group of healthy, affluent women over 50 were zinc deficient. Zinc deficiency appears to be common in older women. This may be in part because they eat less and in part because the food they consume is deficient in zinc.

      It is well known that the immune system weakens with age, and zinc deficiency may be partly to blame. Zinc is needed for night vision and may also slow the progression of macular degeneration. Macular Degeneration is a disorder of the retina that is the leading cause of severe loss of vision in older women.

      A wide variety of health researchers, nutritionists and physicians are finding that zinc is a sustaining factor in abnormal eating behavior. Dr. Laurie Humphries of the University of Kentucky has found that while patients may develop eating disorders for psychological reasons, they are sustained and complicated by the zinc deficiency that results from decreased food intake.

      Diminished Zinc levels may result in a diminished desire to eat because zinc is critical to the senses of taste and smell. In a 1994 summary publication appearing in the Journal for Medical Research, Dr. Alex Schauss reports that studies at Stanford, University of Kentucky, and University of California at Davis found most anorexics and many bulimics were zinc deficient. A five-year study showed an astounding 85 percent remission rate of anorexia nervosa in patients given a zinc supplement. Using zinc supplements resulted in weight gain, better body function and improved mental outlook.

      Rich sources of zinc are oysters, beef, liver, crab, seafood, poultry, nuts and seeds, whole grains, tofu, peanuts and peanut butter, legumes and milk. Zinc found in breast milk is better absorbed than that in formula milk. Fruits and vegetables are not generally good sources of zinc.

The list below provides the zinc content of selected foods in mg. of zinc.

      More than half of the body's zinc supply is found in muscle tissue. Zinc is also found in the bones, eyes, prostate gland, testes, skin and kidneys. Minerals may compete for absorption sites in the intestine. The absorption sites for zinc are the same ones used by iron and copper. Theefore, excess intakes of iron or copper can adversely interfere with zinc absorption. Likewise, excess intake of zinc can impair iron and copper absorption. Phytates and fiber found in unprocessed grains inhibit the bioavailability of zinc and other minerals. Exposure to toxic metals such as lead or cadmium can interfere with the absorption of zinc and displace zinc in its metabolic functions. Whole grain yeast breads enhance the absorption of zinc by producing enzymes that destroy phytates. Sprouting grains also destroys phytates. Zinc from meat products is four times more bioavailable than that found in fibrous grain foods.

      Zinc is easier to absorb in smaller doses. Overall, the body absorbs 15-40% of dietary zinc, depending on the body's requirement. Zinc stored in body tissues does not function as zinc reserves, so the body depends on adequate dietary intake for its daily requirements.

      Zinc is lost in also sweat and through food processing. Canning or cooking in water can deplete the amounts of zinc in food because zinc is water soluble.

      Zinc levels in blood, hair and other tissues are indicators which have been inconclusive and sometimes misleading. In the early 1980s a simple taste test was developed and reported in The Lancet. To create a test solution, dissolve 0.1 percent zinc sulfate (available at health some food stores and your locl pharmacy) in a base of distilled water. You should refrain from eating, drinking or smoking for at least an hour before the test, then place about a teaspoon of the solution in your mouth and swish it around for 10 seconds. If it tastes unpleasant or metallic, your level of zinc is probably adequate. However, if the solution tastes like water, you may be receiving less zinc than you need.

      While a zinc deficiency is a health disaster, once the body's needs have been met, more is not better.

      If you take too much zinc, you may experience zinc toxicity, which may result in abdominal cramping, diarrhea and vomiting.

      Excessive zinc intake will eventually affect the balance and proper ratios to numerous other important nutrients that may include iron, calcium, selenium, nickel, phosphorus, copper, as well as Vitamin A, B1, C, and others.

      Long term overdosing on zinc may also cause, or contribute to gastrointestinal problems, hair loss, anemia, loss of libido, impotence, prostatitis, ovarian cysts, menstrual problems, depressed immune functions, muscle spasms, sciatica, renal tubular necrosis / interstitial nephritis, dizziness and vomiting, among others.

      Zinc toxicity may also (in doses > 80 mg/day) decrease levels of HDL-cholesterol and white blood cells. Impaired cholesterol metabolism may also result from excess intake of zinc supplements.

      The upper limit of safety for zinc established by the Food and Nutrition Board of the Institute of Medicine is 40 milligrams daily for adults.

      The Zinc Tolerable Upper Intake Levels for different life stages are:

      Endurance athletes may develop a zinc deficiency because of dietary deficiencies and increased zinc demands and losses. A high carbohydrate diet has been used by endurance athletes in an attempt to enhance their performance. High carbohydrate diets are low in zinc. If zinc supplements are not being taken, low zinc levels are likely.

      Poor appetite is one potential sign of zinc deficiency. Because zinc is involved in the growth and development of taste buds, deficiency reduces taste and a poor appetite. Zinc deficient individuals also tend to find protein disagreeable, compounding their problem. In female athletes zinc deficiency can result in menstrual cycle irregularities, amenorrhoea and osteoporosis.

      Zinc deficiency in athletes can lead to anorexia, weight loss, decreased endurance, fatigue and an increased risk of osteoporosis.

      Strenuous exercise may contribute to the zinc deficiency by increasing sweat loss and zinc redistribution between blood plasma and red blood cells.

      Zinc Monomethionine is a 1:1 chelated complex of the antioxidants zinc and methionine. Human and animal studies have demonstrated that zinc monomethionine is absorbed better, retained longer and is more effective than other zinc supplements tested. Zinc monomethionine has been shown to enhance immunity, improve male sexual function, nourish the skin, and fight free radical damage.

      Remember that the RDI (Recommended Daily Intake) and RDA (Recommended Daily Allowance) numbers are a statistical estimate of the amounts that prevent individuals from demonstrating deficiency signs and symptoms. The optimum nutrition level is generally higher than the RDI numbers, sometimes much higher. Unfortunately, we do not know what those numbers are. Furthermore, individual needs vary with age, sex, health status and individual genetic makeup. The simplest estimate of optimum zinc intake is assume that it is between the RDI numbers and the maximum tolerance numbers from the table above. It is also likely that foods are deficient in zinc in general, therefore, zinc supplementation is appropriate.

      In general, the sum of the zinc from foods and supplements should not exceed the maximum tolerance estimates, at least for long periods of time.

      Because zinc competes with iron and copper, those taking high doses of zinc supplements may develope deficiencies of these minerals. One way to avoid this is to take a good broad spectrum multi-mineral supplement. It is best to take these at different times to avoid conflict over the absorption channels.

      Zinc is water soluble and is not stores effectively in body tissues. Therefore, for maximum absorption and utilization of supplemental zinc, it is best to take it in divided doses at different times of the day.

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