Evidence Lacking on Zinc Salts and Colds
March 1998; Volume 1: 36
Source: Jackson JL, Peterson C, Lesho E. A meta-analysis of zinc salts lozenges and the common cold. Arch Intern Med 1997;157:2373-2376.
Researchers conducted a meta-analysis of published randomized clinical trials on the use of zinc salts lozenges in colds using a random effects model. Eight clinical trials of treating adults with zinc salts lozenges were identified. After excluding two studies that used nasal inoculation of rhinovirus, six trials were combined and analyzed. The summary odds ratio for the presence of any cold symptoms at seven days was 0.50 (95% confidence interval, 0.19-1.29). The authors conclude that, despite numerous randomized trials, the evidence for effectiveness of zinc salts lozenges in reducing the duration of common colds is still lacking.
COMMENT
The authors note that, "In the United States, the common cold has been estimated to cost more than $3.5 billion a year." And that’s only the direct financial cost—the misery of stuffy, clogged noses has been everywhere this year. Eager zinc manufacturers promote their brands, couple zinc with vitamin C, and warn against inactivation of zinc salts by chelation—a contested claim, at best.Undertaking treatment with zinc (gluconate is the most common form) is not easy: five of the six trials analyzed called for ingestion every two hours while awake until the cold is resolved, or for at least a week. Zinc salts are noxious. An unpleasant aftertaste occurred in 80% of subjects in the best known trial, published in the Annals of Internal Medicine in July 1996, and 20% of subjects were nauseated.
Zinc is found in meat, liver, eggs, seafood, and fortified cereals—not exactly an abundant mineral in a plant-based diet. Even so, women need just 12 mg daily and men 10 mg to make the Recommended Daily Allowance of the National Academy of Sciences. Whether hundreds of milligrams daily can make cough, sore throat, and hoarseness go away sooner remains up for grabs. Excessive zinc can certainly, however, reduce immune response and reduce HDL cholesterol.
Recommendation
Large doses of zinc cannot be generally recommended as a treatment for a common cold—this meta-analysis failed to find good evidence for them. Individual decisions to prescribe zinc, however, may be justified for patients who are aware of its risks, want to attempt a short, time-limited course, are willing to take it precisely as prescribed, and who will report back about its effects. March 1998; Volume 1: 36Subscribe Now for Access
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