A new Britsh study is lending support to the controversial view that zinc gluconate lozenges, widely available at health food stores, can shorten the duration of the common cold.
The study, by leading cold researchers David A.J. Tyrrell and Peter G. Higgins, is the first to demonstrate that the symptoms eased by zinc are actually caused by a cold virus, or rhinovirus.
Their report, at the Seventh International Conference on Virology in Edmonton, Alberta, concluded that "zinc gluconate lozenges are reasonably well tolerated and . . . have a significant effect on the signs and symptoms of colds caused by rhinoviruses . . ." The paper has been accepted for publication in "Antimicrobial Agents and Chemotherapy."
Volunteers in the British Medical Research Council study were quarantined for 48 hours to be sure that they did not have colds or were coming down with them, and then were deliberately inoculated with rhinoviruses into the nostrils.
Some of the exposed participants sucked on a 23 milligram zinc gluconate tablet every two hours for as long as they were awake. The rest were given look-alike and taste-alike dummy tablets. (Volunteers in both groups were told to take no more than 12 tablets a day.)
Two to four days after coming down with their colds, those volunteers who got the real medication were very much better, as measured by, among other things, the number of tissues they were using to wipe their runny noses. On the other hand, volunteers in the placebo group still had symptoms on the sixth day after onset of their colds.
In an earlier study, the MRC researchers also found that zinc gluconate 24 hours before exposure to a cold -- used in the same way as for therapy -- reduces the chances of actually getting one by about a third. They do not, however, recommend that people take zinc gluconate regularly for the prevention of colds because of evidence that routine medication with it can injure white blood cells and cause a harmful rise in blood cholesterol.
Another thing the British researchers discovered, their paper reports, is that zinc gluconate "had no significant effect on the rate or amount of virus excreted by the volunteers." In a telephone interview, Higgins said he did not know why the virus count remained the same, or even why zinc speeds recovery from colds. Nor, he added, had they tested the compound against all the many strains of rhinovirus that can produce colds, although the strain studied is among the most common.
The apparent value of zinc was first noticed in 1979 after a 3-year-old leukemia patient, taking zinc for reasons related to her illness, also was relieved of cold symptoms. A follow-up study by George Eby, father of the girl, and Dr. William Halcomb of Austin, Tex., had impressive results, but they were unable to show an actual link to rhinoviruses.
Zinc therapy for colds remains controversial. Dr. William Jordan, director of the microbiology and infectious disease program at the National Institute of Allergy and Infectious Diseases, considers the results of the British study "modest" and says he "wouldn't buy any stock in zinc gluconate."
Furthermore, two studies -- one from Australia and the other from the University of Virginia at Charlottesville -- were published in the July issue of Antimicrobial Agents and Chemotherapy and were in agreement that zinc has no beneficial effects on colds.
Just why is not clear. But it may be significant that the Australian study used zinc acetate instead of zinc gluconate and that the zinc gluconate Dr. Jack Gwaltney and his colleagues at the University of Virginia used for their study was prepared with magnesium sulfate, a chemical which still another study suggests may actually stimulate cold viruses.