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.

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.

Zinc is a metallic element present in soil.

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.

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)

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.

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.

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.

Postmenopausal 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.

There 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.

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

Quinolone 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).

Tetracyclines 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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