What does zinc do?
In double-blind trials, zinc lozenges have reduced the duration of colds in adults,1 2 3 but have been ineffective in children.4 The ability of zinc to shorten colds may be due to a direct, localized anti-viral action in the throat. For the alleviation of cold symptoms, lozenges providing 13–25 mg of zinc, in the form of zinc gluconate, zinc gluconate-glycine, or zinc acetate, are used, typically every two hours while awake, but only for several days. The best effect is obtained when lozenges are used at the first sign of a cold.
Lozenges containing zinc gluconate, zinc gluconate-glycine, or zinc acetate have been effective, whereas most other forms of zinc and lozenges flavored with citric acid,5 tartaric acid, sorbitol, or mannitol, have been ineffective.6 Trials using forms other than zinc gluconate, zinc gluconate-glycine, or zinc acetate have failed, as have trials that use insufficient amounts of zinc.7 Therefore, until more is known, people should only use zinc gluconate, zinc gluconate-glycine, or zinc acetate.
Zinc reduces the body’s ability to utilize the essential mineral copper. (For healthy people, this interference is circumvented by supplementing with copper, along with zinc.) The ability to interfere with copper makes zinc an important therapeutic tool for people with Wilson’s disease—a genetic condition that causes copper overload.
Zinc supplementation in children in developing countries is associated with improvements in stunted growth, increased weight gain in underweight children, and substantial reductions in the rates of diarrhea and pneumonia, the two leading causes of death in these settings.8 9 10 Whether such supplementation would help people in better nourished populations remains unclear.
A small, preliminary trial has found zinc sulfate to be effective for contact dermatitis (a skin rash caused by contact with an allergen or irritant).11 Participants with active skin rashes took approximately 23 mg of zinc (in the form of zinc sulfate) three times daily, for one month. 73% of those taking the zinc sulfate had complete resolution of their skin rashes, while the remaining participants had a 50–75% improvement. Further trials are needed to confirm these preliminary findings, however.
Where is zinc found?
Zinc has been used in connection with the following conditions
Who is likely to be deficient of zinc?
Even in developed countries, low-income pregnant women and pregnant teenagers are at risk for marginal zinc deficiencies. Supplementing with 25–30 mg per day improves pregnancy outcome in these groups.12 13
People with liver cirrhosis appear to be commonly deficient in zinc.14 This deficiency may be due to cirrhosis-related zinc malabsorption.15
People with Down’s syndrome are also commonly deficient in zinc.16 Giving zinc supplements to children with Down’s syndrome has been reported to improve impaired immunity17 and thyroid function,18 though optimal intake of zinc for people with Down’s syndrome remains unclear.
Children with alopecia areata (patchy areas of hair loss) have been reported to be deficient in zinc.19 20
The average diet frequently provides less than the Recommended Dietary Allowance for zinc, particularly in vegetarians. To what extent (if any) these small deficits in zinc intake create clinical problems remains unclear. Nonetheless, a low-potency supplement (15 mg per day) can fill in dietary gaps. Zinc deficiencies are more common in alcoholics and people with sickle cell anemia, malabsorption problems, and chronic kidney disease.21
How much zinc is usually taken?
Are there any side effects or interactions with zinc?
Preliminary research had suggested that people with Alzheimer’s disease should avoid zinc supplements.24 More recently, preliminary evidence in four patients actually showed improved mental function with zinc supplementation.25 In a convincing review of 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.26
Zinc inhibits copper absorption. Copper deficiency can result in anemia, lower levels of HDL (“good”) cholesterol, or cardiac arrhythmias.27 28 29 Copper intake should be increased if zinc supplementation continues for more than a few days (except for people with Wilson’s disease).30 Some sources recommend a 10:1 ratio of zinc to copper. Evidence suggests that no more that 2 mg of copper per day is needed to prevent zinc-induced copper deficiency. Many zinc supplements include copper in the formulation to prevent zinc-induced copper deficiency. Zinc-induced copper deficiency has been reported to cause reversible anemia and suppression of bone marrow.31
Marginal zinc deficiency may be a contributing factor in some cases of anemia. In a study of women with normocytic anemia (i.e., their red blood cells were of normal size) and low total iron-binding capacity (a blood test often used to assess the cause of anemia), combined iron and zinc supplementation significantly improved the anemia, whereas iron or zinc supplemented alone had only slight effects.32 Supplementation with zinc, or zinc and iron together, has been found to improve vitamin A status among children at high risk for deficiency of the three nutrients.33
Zinc competes for absorption with copper, iron,34 35 calcium,36 and magnesium.37 A multimineral supplement will help prevent mineral imbalances that can result from taking high amounts of zinc for extended periods of time.
N-acetyl cysteine (NAC) may increase urinary excretion of zinc.38 Long-term users of NAC may consider adding supplements of zinc and copper.
Are there any drug interactions?