The ongoing debate over the role of zinc in combating the common cold was reinvigorated today by a report that suggests the supplement might modestly reduce cold duration and severity -- or maybe even prevent it. But the report, published as a Cochrane Review, raised questions among doctors about the quality of the findings and whether people should start taking zinc for colds.
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.
"This is an important review because many people use zinc products to either treat or prevent common colds," said Dr. William Schaffner, chair of preventive medicine at Vanderbilt University Medical Center in Nashville.
In theory, zinc might prevent the cold virus from attaching to cells in the nose and throat and stop it from replicating in cells that are already infected -- an effect that has been difficult to prove.
All 15 trials reviewed 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 -- the gold standard in clinical trials.
Furthermore, zinc lozenges are known to have a bad taste that could be discernable from that of a placebo, Singh and Ranjan Das reported.
Although the review suggests the effects of zinc in fighting the common cold are positive, they're mild. 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.
"That is a lot of zinc," said ABC News chief health and medical editor Dr. Richard Besser. "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."
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.
In addition to reducing the duration and severity of colds, Singh and Ranjan Das concluded 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.