Zinc is an essential trace mineral that occurs in greater amounts than any other trace mineral except iron. Its functions are varied and numerous, including synthesis of cholesterol, protein and fats, releasing vitamin A from the liver, assisting the immune system and cell growth, being required for vision, taste perception, prostrate reproductive health and insulin function, metabolizing alcohol, and protecting against copper and heavy metal toxicity such as cadmium and lead. Zinc absorption is enhanced by soy protein, red wine, glucose, and lactose. Iron, copper, calcium and phytates inhibit absorption.

The Recommended Daily Amount is 15mg; the optimal daily intake is 30-50mg; the average daily intake in the U.S. is 10mg per day. Therapeutic doses are 30-350mg but care must be taken to avoid toxicity. Signs of toxicity include diarrhea, nausea and vomiting. Watch for copper deficiency if supplementing zinc for an extended period of time.

Zinc at doses of 20mg and above may cause stomach upset and/or nausea so it should always be taken with food. Long-term zinc supplementation above 50mg has been shown to decrease HDL cholesterol and increase total cholesterol. This may be due to an induced copper deficiency. In addition, copper deficiency anemia can occur as well. Zinc should always be taken with copper in a 10 to 1 through 30 to 1 zinc to copper ratio. Large doses of zinc may also promote folate deficiency.

The best natural sources of zinc include: oysters, meats, wheat germ, hard cheeses, Swiss chard, lima beans, potatoes, oats, green leafy vegetables, pumpkin and squash seeds, soy beans/foods, tuna, kidney beans, ginger root, peas, leeks, lentils, cashews, sunflower seeds (and tahini), pecans, peanuts, filberts. Other sources include herring, poultry, eggs, buckwheat, brown rice, millet, corn, black-eyed peas, green beans, chickpeas, spinach, green onion, and sprouted grains.

Note  Food processing removes a large amount of zinc as well as other trace elements. For example, whole brown rice has more than 4 times the zinc that polished white rice has. Molasses has 42 times more zinc than an equal amount of white sugar. By weight, the germ part of wheat has 15 times more zinc than can be found in white flour.

Symptoms of deficiency include growth retardation (as related to protein metabolism), delayed sexual development, mild anemia, decreased taste sensation, decreased or loss of sense of smell, delayed wound healing, glossitis, angular stomatitis, and diverse forms of skin lesions (including eczema, psoriasis, acne). Night blindness, associated with an inability to mobilize retinol from the liver, may also be caused by zinc deficiency. About 25% of people who have an impairment in taste and or smell are suffering from an outright zinc deficiency.

Another common condition that can develop is Acrodermatitis Enteropathica, an autosomal recessive disease that is characterized by zinc malabsorption. This results in eczematoid skin lesions, alopecia, diarrhea, and concurrent bacterial and yeast infections. Gastrointestinal malabsorption can lead to deficiency.

Other symptoms often associated with decreased zinc include hang nails, inflammation of nail cuticles, white spots on fingernails, transverse lines and poor nail growth, sleep and behavioral disturbances, psychiatric illness, all types of inflammatory bowel disease, impaired glucose tolerance, dandruff, arthritis and alcoholism.

Supplemental treatment with an intranasal zinc gluconate preparation for nine days (3 days before, and 6 days after, inoculation with rhinovirus) with had no effect on total symptom scores, rhinorrhea, nasal obstruction, or the rate of
infection in a placebo-controlled study of 91 volunteers experimentally infected with rhinovirus. [Clin Infect Dis 2001;33(11): pp.1865-1870]

Antagonists:
Alcohol, chelating compounds, diuretics, oral contraceptives, penicillamine (causes zinc to be chelated and excreted along with intended heavy metals), prednisone/prednisolone: causes increased urinary excretion of zinc (Buist, 1984; 4 (3): p.114)

Interactions:
Copper, calcium and iron taken in large doses can interfere with zinc absorption and induce a deficiency, especially in pregnant women. People who take large doses of iron to correct anemia when they are already borderline zinc deficient can easily create a true zinc deficiency.