Efficacy of zinc in common cold - Review of clinical trials

By Dr. Ananya Mandal, MDFeb 15 2011

A new study has added to the existing literature that debates the role of zinc in combating the common cold. It suggests that the supplement might modestly reduce cold duration and severity or maybe even prevent it. The report was published as a Cochrane Review.

Drs. Meenu Singh and Rashmi Ranjan Das from the Postgraduate Institute of Medical Education and Research in Chandigarh, India, examined the results from 13 previously therapeutic trials and two preventive trials of zinc in more than 1,300 subjects. Overall, subjects with colds who took zinc were less likely to have symptoms seven days later, and healthy subjects were less likely to get a cold if they took zinc prophylactically.

Dr. William Schaffner, chair of preventive medicine at Vanderbilt University Medical Center in Nashville said, “This is an important review because many people use zinc products to either treat or prevent common colds.”

In the review all the 15 trials were blinded, meaning the researchers were unaware which subjects were taking zinc. But only six were placebo-controlled, meaning the patients were also unaware of what they were taking. These latter six are the gold standard in clinical trials. The authors add that it is difficult to conduct zinc trials against dummy or placebo since zinc lozenges are known to have a bad taste.

The review concludes that promptly treating a cold with zinc reduced its duration by an average of one day, and taking zinc daily for prevention reduced the risk by roughly a third. But these modest pros should be weighed against the cons -- bad taste, nausea and the cost of zinc. Forty-eight zinc lozenges cost as much as $10.99. And according to the review, it takes one lozenge every 1.5 to 2 hours to quash a cold and one daily for at least five months to prevent one. The dose of zinc used in the studies reviewed varied from 10 to 23.7 mg in lozenge or syrup form. The tolerable upper intake level for zinc is 40 mg, and daily intakes of 150 to 450 mg have been linked to chronic health effects including reduced immune function, according to the National Institutes of Health.

Dr. Richard Besser on the amount of zinc necessary added, “That is a lot of zinc… If you go that route, there is a risk of unwanted side effects including nausea and altered taste. However, the study does not say how frequently these occur.” In fact in June 2009 the U.S. Food and Drug Administration warned consumers to stop using a zinc-containing intranasal cold remedy when reports of some users losing their sense of smell surfaced.

However Singh and Ranjan Das believe that zinc can also reduce school absences and antibiotic use. According to a 2003 study published in Archives of Internal Medicine, more than a third of patients who see a doctor for a cold received an antibiotic prescription. In the United States common cold prompts up to 100 million doctor’s visits, 189 million missed school days and 276 missed work days each year, costing billions of dollars in health care expenses and work losses.

Dr. Kay Dickersin, a professor of epidemiology at Johns Hopkins Bloomberg School of Public Health and director of the U.S. Cochrane Center who was not involved in the research said, “I think there is a need for more research so we can get a sense of how well zinc works or if it even does work.”

Besser said he would not recommend zinc for prevention or treatment of colds. For preventing a cold, Besser suggests frequent hand washing or using an alcohol-based hand sanitizer especially during cold and flu season and around young children. For treating a cold, most over-the-counter drugs are ineffective. He explained, “Acetaminophen and ibuprofen are effective pain and fever medications… Some people benefit from a nasal decongestant. And for the uncomfortable nose there are tissues, salt water nose drops and petroleum jelly.”