Common Cold - Can Zinc Cure the Common Cold?
Can Zinc Cure the Common Cold?
by Kathleen Meister
The U.S. population experiences about a billion cases of the common cold per year-two to four cases annually for a typical adult, six to eight cases for a child. Some people catch a cold as often as 12 times a year. This viral infection is more bothersome than dangerous. But it's a major economic burden-the single largest cause of job absenteeism in the United States: 15 million sick days each year. The common cold is the commonest cause of visits to physicians. And sales of over-the-counter cough and cold medications total more than $3 billion annually.
As physicians have long told their patients, a cold usually lasts about seven days if you treat it, and about a week if you don't. The medicines people generally take for a cold-aspirin, cough suppressants, and decongestants, for example-merely relieve specific symptoms; they don't alter the duration of the infection.
Recently, however, much enthusiasm has arisen concerning zinc gluconate, a mineral compound that may be able to shorten a cold. No cold medicine has proved effective at this. Zinc gluconate products marketed as cold remedies are available in lozenge form. In two recent controlled trials-one involving employees of the Cleveland Clinic Foundation; the other, students at Dartmouth College-the colds of subjects who were given zinc gluconate lozenges were significantly shorter than those of subjects given placebos. On average, the duration of cold symptoms lasted three to four fewer days in the zinc-lozenge subjects.
Both of these studies appear sound: In both, the number of subjects was substantial (100 in Cleveland, 73 at Dartmouth). And both studies were double-blind; i.e., during the experiment, neither the subjects nor the health professionals who evaluated their symptoms knew who was receiving the zinc gluconate. Nevertheless, questions concerning the effectiveness and safety of using zinc gluconate to treat a cold remain to be settled.
Although the two most recent trials suggested that zinc lozenges were significantly more ef-fective against the common cold than were their placebo counterparts, four of the six prior zinc-lozenge trials had not. proponents of the treatment contend that differences in the for- mulation of the lozenges accounted for the differences in results. But there is no clear evidence of this.
The question of by what means zinc might affect the course of a cold has not been resolved. Hypotheses that zinc inhibits the replication of cold viruses, prevents their entry into cells, and fights colds by correcting subclinical zinc deficiencies have not been substantiated.
The company that manufactured the lozenges used in the Cleveland Clinic and Dartmouth studies markets its zinc-lozenge products with claims that do not inspire trust. The Quigley Corporation describes them as "clinically proven" and "Homeo-pathic." Homeopathy (see priorities, Vol. 9, No. 1, 1997, p. 45) is a medical system rejected by virtually all physicians educated in U.S. medical schools. According to the label on "Cold-Eeze," each zinc lozenge contains "13.3 mg of ionic zinc from Zincum Gluconicum 2X (104 mg zinc gluconate trihydrate) equivalent to Zincum 3X." In an e-mail reply to the American Council on Science and Health, the Quigley Corporation's customer relations department interpreted the preceding description: Each lozenge contains 13.3 mg of zinc, and this zinc is derived from a homeopathic preparation. This dose is very much higher than the "active-ingredient" levels of typical homeopathic preparations, many of which contain either none of the "basic remedy" or an amount too small to have any appreciable effect. (On October 3, 1997, FDA spokesperson Dilcia Granville told priorities editor Jack Raso that the American Institute of Homeopathy had recently recognized zinc gluconate as a homeopathic substance, that Cold-Eeze was a legitimate homeopathic product, and that FDA jurisdiction over such products is "very limited.")
Zinc gluconate has an unpleasant taste. Even when flavoring agents accompany it, many people perceive a bad taste or an aftertaste. In the Cleveland Clinic study, 80 percent of the zinc-taking subjects reported bad tastes from taking their medicine, while only 30 percent of the placebo group reported such. Twenty percent of the zinc group, versus 4 percent of the placebo group, reported nausea from taking their medicine.
zinc-lozenge use unsupervised by a health professional may not be safe. Zinc is an essential nutrient, but it is toxic at high dosages. Long-term ingestion of the trace element at levels significantly above the Recommended Dietary Allowance-which, for adults, ranges from 12 to 16 mg daily-can lower copper status, weaken various immune responses, and decrease levels of HDL-cholesterol (a compound that tends to be protective against heart disease). Lozenges of the sort used in the Cleveland Clinic study contain between 11.5 and 14.5 mg of zinc. While such levels are within the adult RDA range, labels typically recommend a daily intake of 6 lozenges. Such an intake of zinc might cause health problems if the intake is habitual or if one takes zinc-containing dietary supplements as well.
Many people may be using zinc lozenges habitually, to prevent a cold or to nip in the bud what they suspect is a cold. On its website, the Quigley Corporation recommends taking the lozenges "before the cold really develops." The company also recommends giving zinc lozenges to every cohabitant whenever one has a cold. And it suggests that lozenge intake is advisable for relief of nasal allergy symptoms, for treating canker sores, and, as a preventive, for persons who "are at a constant high risk of infection." Nasal allergy symptoms and canker sores often last much longer than a cold. Such practices could lead to toxicity.
Zinc lozenges may not be a cold cure, but they're probably worth a try. As with any medicine or dietary supplement, caution is in order. Those who decide to use zinc lozenges:
- should use them only to treat what is obviously a cold;
- should not use them to treat any long-term condition;
- should not use them to prevent a cold or any other condition;
- should not take more than the recommended number of lozenges; and
- should not use any zinc-containing dietary supplement during treatment.
Kathleen Meister, M.S., is a freelance medical writer and a former ACSH research associate.