Zinc is an essential trace mineral, which, next to iron, is the second most abundant trace mineral in the body. It is a component in over 200 enzymes. Zinc is stored primarily in muscle but high concentrations are also found in red and white blood cells and the retina. It is also found in bones, skin, kidney, liver, and pancreas. In men, the prostate gland contains more zinc than any other organ.

Zinc is a part of some important antioxidant compounds, including superoxide dismutase (SOD) and zinc monomethionine. It protects the liver from chemical damage, helping with detoxification of the body. It is required for a healthy immune system. Taking zinc supplements has been shown to reduce infection and speed wound healing. Studies have shown it helps treat and prevent acne. It is essential for proper growth and development, especially early in life. It is necessary to maintain proper vision, taste, and smell.

Zinc deficiency may be a more common problem than previously thought, especially as people age. In clinical studies on the effects of zinc supplementation in the elderly, zinc improved immune system function, reduced the incidence of illness, and decreased the incidence of anorexia.

Recent research has been conducted to determine the true value of zinc lozenges in preventing or reducing cold symptoms.
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Dietary Sources

Zinc absorption from foods varies from 20% to 40% of ingested zinc. Zinc from animal foods is the best absorbed form. When bound with the phytates or oxalates in vegetable sources, zinc is less available, and vegetable fiber itself impedes the absorption of zinc. Dairy products and eggs contain fair amounts of zinc, but again, it may be poorly absorbed from these sources.

The following foods contain high amounts of zinc in the most absorbable form.

Oysters (richest source)
Red meats
Shrimp, crab, and other shellfish
Other good sources, but which may be less absorbable, include legumes (especially lima beans, black-eyed peas, pinto beans, soybeans, peanuts) whole grains, miso, tofu, brewer’s yeast, cooked greens, mushrooms, green beans, and pumpkin seeds.
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Constituents/Composition

Zinc is a metallic element present in soil.
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Commercial Preparations

The most commonly used zinc supplement has been zinc sulfate. This is the least expensive form, but it may cause gastric irritation and is less absorbable than other forms. It is usually prescribed as 220 mg zinc sulfate, which provides approximately 55 mg of elemental zinc. More absorbable forms such as the following are available.

Zinc picolinate
Zinc citrate
Zinc acetate
Zinc glycerate
Zinc monomethionine
These forms come in capsules supplying 30 or 50 mg of elemental zinc. The amount in milligrams per capsule of these other zinc compounds can vary, according to the percentage of elemental zinc contained. Zinc lozenges are also available, which supply varying amounts of zinc and are used for treating colds.
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Therapeutic Uses

Benefits of zinc include the following.

Treats depressed immunity
Improves wound healing
Treats and may prevent acne
May prevent macular degeneration
Treats anorexia nervosa (anorexia is a symptom of zinc deficiency, and the teenage population is at higher risk for zinc deficiency due to dietary habits)
Improves male fertility and sexual function, especially among smokers
Treats rheumatoid arthritis
Treats Wilson’s disease (a disorder of excess copper storage)
Decreases taste alteration during cancer treatments
Improves sense of taste and smell
Some conditions may impair zinc absorption, or increase the need for zinc. Individuals with the following conditions may benefit from zinc supplementation.

Acrodermatitis enteropathica (the inherited disease of zinc malabsorption)
Pregnancy, lactation
Alcoholism
Diabetes
Kidney disease, dialysis
Celiac disease
Inflammatory bowel disease, ulcerative colitis
Chronic diarrhea
Pancreatic insufficiency
Oral contraceptive use
Prostate problems (BPH, prostatitis, cancer)
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Dosage Ranges and Duration of Administration

The RDA for zinc is as follows.

Infants to 1 year: 5 mg
1 to 10 years: 10 mg
Males over 10 years: 15 mg
Females over 10 years: 12 mg
Pregnant females: 15 mg
Lactating females: (0 to 6 months) 19 mg, (6 to 12 months) 16 mg
Therapeutic ranges (elemental zinc):

Men: 30 to 60 mg daily
Women: 30 to 45 mg daily
Doses over this amount should be limited to only a few months under the supervision of a health care professional.
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Side Effects/Toxicology

Zinc is the least toxic trace mineral. Symptoms of toxicity are GI irritation and vomiting, usually occurring after a dose of 2,000 mg or more has been ingested. Studies have confirmed that up to 10 times the RDA (150 mg) taken even over time was not toxic. Doses this high are unnecessary and interfere with the assimilation of other trace minerals such as copper and iron.

Too much zinc (over 150 mg/day over time) lowers HDL cholesterol and raises LDL cholesterol, an undesirable effect. Megadoses of zinc are reported to depress immune function. Studies on this have been inconclusive, and further research is needed.

Zinc sulfate can cause gastric irritation, but another form can be used instead if this occurs. Other reported side effects of zinc toxicity are dizziness, headache, drowsiness, increased sweating, muscular incoordination, alcohol intolerance, hallucinations, and anemia.
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Warnings/Contraindications/Precautions

Because of the multiple interactions zinc has with other nutrients, it is advisable to take a balanced multiple vitamin/mineral preparation that contains zinc as well as copper, iron, and folate, to help prevent deficiencies of these nutrients.
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Interactions

Estrogens; ProgestinsPostmenopausal women treated with conjugated estrogens and medroxyprogesterone acetate experienced reductions in zinc excretion of 35% after 3 months and 26% after one year (Herzberg et al. 1996). The reduction was more pronounced in women with osteoporosis who had elevated zinc excretion at the beginning of the study. The clinical significance of this interaction is unknown.

HydralazineThere is a case report of a 58-year-old woman who developed a lupus erythematosus-like syndrome within 1 week following the addition of zinc sulphate therapy (200 mg po tid) to her drug regimen (30 to 200 mg/day hydralazine; 120 to 640 mg/day propranolol; polythiazide; potassium chloride; propylthiouracil; and thyroxine) for the treatment of leg ulcers (Fjellner 1979). Her symptoms included fever, abdominal distress, facial butterfly rash, enlargement of the leg ulcers, oral ulcers, and maculopapular eruptions on legs, trunk, and arms. Withdrawal of zinc prompted clinical improvement, including healing of the oral ulcers and remission of the fever and abdominal distress. However, the patient’s condition did not resolve completely until all the medications except thyroxine also were discontinued.

Nonsteroidal Anti-inflammatory Drugs (NSAIDs)Zinc interacts with anti-inflammatory medications by forming complexes with these drugs (Dendrinou-Samara et al. 1998).

Quinolone AntibioticsQuinolone antibiotics form chelates with metal cations, such as aluminum, magnesium, calcium, iron, zinc, copper, and manganese (Kara et al. 1991; Li et al. 1999), which significantly reduces the absorption of these medications (Balfour and Wiseman 1999; Brouwers 1992; Campbell and Hasinoff 1991). Dietary supplements and antacids containing aluminum and magnesium should be taken two to four hours before or after administration of these antibiotics (Hines Burnham et al. 2000; Li et al. 1999).

Tetracycline DerivativesTetracyclines form chelates with divalent and trivalent cations, including iron, aluminum, magnesium, and calcium (Neuvonen 1976). These chelates are poorly soluble and can significantly reduce the absorption and efficacy of tetracyclines (Hines Burnham et al. 2000; Neuvonen 1976). However, in an in vitro study, zinc-drug interactions in gastrointestinal fluid influenced the bioavailability of both zinc and tetracycline or tetracycline analogs (Brion et al. 1985).
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References

Balfour JA, Wiseman LR. Moxifloxacin. Drugs. 1999;57(3):363-374.

Brion M, Lambs L, Berthon G. Metal ion-tetracycline interactions in biological fluids. Part 5. Formation of zinc complexes with tetracycline and some of its derivatives and assessment of their biological significance. Agents Actions. 1985;17:230-242.

Brouwers JR. Drug interactions with quinolone antibacterials. Drug Saf. 1992;7(4):268-281.

Campbell NR, Hasinoff BB. Iron supplements: a common cause of drug interactions. Br J Clin Pharmacol. 1991;31(3):251-255.

Dendrinou-Samara C, Tsotsou G, Ekateriniadou E, et al. Anti-inflammatory drugs interacting with Zn(II), Cd(II) and Pt(II) metal ions. J Inorg Biochem. 1998; 71: 171-179.

Eby GA. Zinc ion availability—the determinant of efficacy in zinc lozenge treatment of common colds. J Antimicrob Chemother. 1997;40:483-493.

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Fjellner B. Drug-induced lupus erythematosus aggravated by oral zinc therapy. Acta Dermatovener. 1979;59:368-370.

Fortes C, Forastiere F, Agabiti N, et al. The effect of zinc and vitamin A supplementation on immune response in an older population. J Am Geriatr Soc. 1998;46:19-26.

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Golik A, Zaidenstein R, Dishi V, et al. Effects of captopril and enalapril on zinc metabolism in hypertensive patients.J Am Coll Nutr. 1998;17:75-78.

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Herzberg M, Lusky A, Blonder J, Frenkel Y. The effect of estrogen replacement therapy on zinc in serum and urine.Obstet Gynecol. 1996;87(6):1035-1040.

Hines Burnham, et al, eds. Drug Facts and Comparisons. St. Louis, MO:Facts and Comparisons; 2000:1295.

Kara M, Hasinoff BB, McKay DW, et al. Clinical and chemical interactions between iron preparations and ciprofloxacin. Br J Clin Pharmacol. 1991;31(3):257-261.

Leake A, Chisholm GD, Habib FK. The effect of zinc on the 5a-reduction of testosterone by the hyperplastic human prostate gland. J Ster Biochem. 1984;20:651-655.

Li RC, Lo KN, Lam JS, et al. Effects of order of magnesium exposure on the postantibiotic effect and bactericidal activity of ciprofloxacin. J Chemother. 1999;11(4):243-247.

Lieberman S, Bruning N. The Real Vitamin & Mineral Book. 2nd ed. New York, NY: Avery Publishing Group; 1997.

Murray M. Encyclopedia of Nutritional Supplements.Rocklin, Calif: Prima Publishing; 1996.

Neuvonen PJ. Interactions with the absorption of tetracyclines. Drugs. 1976;11(1):45-54.

Pronsky Z. Food-Medication Interactions. 9th ed. Pottstown, Pa: Food-Medicine Interactions; 1995.

Sazawal S, Black RE, Jalla S, et al. Zinc supplementation reduces the incidence of acute lower respiratory infections in infants and preschool children: a double-blind, controlled trial. Pediatrics. 1998;102(part 1):1-5.

Shealy CN. The Illustrated Encyclopedia of Healing Remedies. Boston, Mass: Element Books Inc.; 1998.

Somer E. The Essential Guide to Vitamins and Minerals.New York, NY: HarperCollins Publishers, Inc.; 1995.

Whitney E, Cataldo C, Rolfes S. Understanding Normal and Clinical Nutrition. St. Paul, Minn: West Publishing Co.; 1987

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