Have a Cold? Think About Zinc

Medically Reviewed by Merle Diamond, MD

Aug. 14, 2000 -- Sneezes, sniffles, that all over blah, achy feeling ... the average American gets between two and six colds a year, and so far, treatments have been ineffective at snuffing them out. But now researchers have found that zinc lozenges may actually cut the time spent suffering from a cold and lessen the symptoms.

In a study that appears in the current issue of the Annals of Internal Medicine, researchers from Wayne State University in Michigan found that patients who took zinc lozenges recovered almost twice as quickly as those who took a placebo. These findings fly in the face of at least five previous trials that didn't show a beneficial effect of zinc.

Led by Ananda Prasad, MD, PhD, a professor of medicine at Wayne State University, the researchers gave either zinc lozenges or a placebo to 48 individuals who had come down with cold symptoms within the previous 24 hours. Each person had to have at least two standard cold symptoms, such as sneezing, sore throat, fever, cough, and muscle aches.

The colds of patients taking the zinc lozenges lasted an average of four and a half days, while the colds of those taking the placebo had symptoms for eight days. Coughing stopped in the zinc group in half the time of the placebo group, and runny noses cleared up about two days sooner.

Prasad acknowledges in the study that previous research has not had such encouraging results. He points out to WebMD, however, that certain problems in previous studies may account for the differences in results. Some of the studies, he says, may have used a type of lozenge that doesn't release the zinc properly when a person takes it in his mouth.

"The dosage also has to be adequate," Prasad says. "I think one study used half the dose that we did, and the zinc must be taken within 24 hours of symptom onset."

Ronald Turner, MD, doesn't think this study will have much impact on usage by the public at large. "The data on zinc treatment have been extremely inconsistent from study to study," he says. "And zinc has been available to the public for some time. The product is available as a dietary supplement, and usage is probably unrelated to physician recommendation." Turner, who was not involved in the study, is a professor of pediatrics at the Medical University of South Carolina, and he has done unrelated research on zinc.

In an editorial that accompanied the study, Norman Desbiens, MD, with the University College of Medicine in Chattanooga, questions whether the study was properly "blinded," meaning, were the participants completely unaware of whether they were taking the placebo or the zinc. For the conclusions to be accurate, this is a very important issue in any study that uses a placebo to measure the effectiveness of a medication.

Turner agrees. "Inadequate blinding has been a consistent criticism of the zinc studies, and these authors do not appear to have adequately addressed the issue."

For example, the patients were asked to guess whether they were taking the placebo or the zinc. About half of those taking the zinc, and around a quarter taking the placebo, identified the lozenges correctly. But the researchers felt that these numbers were not high enough to negatively influence the results.

However, Desbiens feels the fact that more than three and a half times as many participants who received zinc correctly guessed that they were given zinc, may have affected the results of the study. "I suspect that the zinc and placebo had detectable differences, and therefore, a blind was not completely established," he writes.

Prasad writes that a test was done with healthy people who were given both types of lozenges, and it "showed that the zinc and placebo lozenges were indistinguishable in taste." He points out that none of the people involved in the study had ever previously used zinc lozenges, and in fact, they could not participate if they had used zinc in the past.

"This is the question I don't understand," Prasad tells WebMD, "how they would know if they've never had zinc or if they only taste one lozenge."

Everyone was only given one kind of lozenge -- either zinc or the placebo, he says, and they had no opportunity to taste the other kind. "It would be one thing if they had both kinds, but they didn't. So how would they be able to detect a difference in taste?"

The most common side effects from taking the zinc were a dry mouth and constipation. But since the amount of zinc that the study patients took is five times the current RDA of 15 mg, the researchers caution that zinc lozenges should not be taken for more than three days at a time. They recommend that if a person does not improve after three days of zinc treatment, then he should be evaluated for other type of respiratory illnesses or allergies.

Desbiens isn't convinced that taking zinc will help a cold, but the researchers disagree, saying their results show zinc can reduce the average duration and severity of the common cold.

"I think our results are very clear-cut," Prasad says. "The editorialist is saying that if they knew it was the zinc, it might have had an effect on their perception of whether or not they were getting better.

"But we measured symptoms," he adds. "It's hard to say you don't have symptoms if you're coughing or sneezing. Some of the people I recruited were physicians, and they're highly critical people and not easily convinced. So when they were cured in three days, they came to tell me and let me know."

The study was supported in part by an unrestricted grant from the George and Patsy Eby Research Foundation. George Eby holds patent rights to zinc lozenges and supplied both the zinc and placebo lozenges for this study. But Prasad writes the research funds were "unrestricted," and "the authors have neither industry connections nor personal financial conflicts of interest related to this study."