A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Can zinc lozenges cure the common cold?

February 6, 1998

Dear Cecil:

Why are people bothering with getting colds any more? The site www.coldcure.com has been around for a couple years now and the product for stopping common cold symptoms is available in many places (Wal-Mart for one). Could you check out that site and apply your skills to either (1) debunk it or (2) confirm it?

I first read about the "cure" in the 1980s in one of the science news magazines. As long as I used it at the first signs of a cold, it went away the same day. Now that the discoverer has a decent-tasting formulation, it is not only effective but palatable. It is astounding that now that there is a "cure for the common cold," so few people acknowledge it. I do not believe in authority or anecdotes, but this "cure" has clinical studies behind it. What gives with the ignorance?

Cecil replies:

Your columnist wants a cold cure as much as the next guy, William. (Sniffle.) But let's look at this objectively. Somebody announces Surefire Cold Cure number 1,000. Previous attempts have gone 0-for-999. (Hack, wheeze.) You believe this one's different. The rest of the world evidently doesn't (although the thing has gotten loads of publicity). You may think you've got a better grasp of the science, but the world's got a better grasp of the (honk) odds.

The cure we're talking about is sucking on zinc lozenges. George Eby, who came up with the idea and runs the Web site you mentioned, is currently big on the benefits of zinc acetate, but other formulations such as zinc gluconate are also popular. One brand of pill combines zinc with echinacea, a plant extract touted for its antiviral properties. Might as well wash it down with some chicken soup — a lot of people still believe in that, too.

Here's the story to date: 1979: George Eby's three-year-old daughter starts coming down with a cold. Since her immune system has been suppressed following leukemia treatment, he fears that she's in for a nasty one. She sucks on a zinc pill. Two hours later her symptoms have vanished. Whoa, thinks George. He begins researching zinc's curative powers. 1984: Eby and associates report in a medical journal that sucking on zinc gluconate lozenges signicantly reduced the average duration of cold symptoms in a group of 65 patients. Other researchers subsequently report similar results.

Skeptics are quick to attack. Among other criticisms, they claim zinc lozenges have a distinctively yucky taste that may have skewed the results. One study notes sarcastically: "The significant reduction in the duration of common colds with zinc gluconate lozenges … may be due to … the subjects' belief that anything tasting as bad as zinc and with as much aftertaste as zinc must be good medicine" (Farr and Gwaltney, 1987).

A related possibility: patients were disinclined to report a recurrence of cold symptoms for fear they'd have to resume taking those godawful pills. Several subsequent studies that try to minimize the problem of taste (for example, by making sure the placebo used as a control tastes equally bad) find that zinc lozenges have little or no effect on colds.

Zinc advocates don't give up. They argue that the lozenges used in the negative studies were of a type that inactivated the zinc. 1996: A team of researchers at the Cleveland Clinic Foundation publish a study claiming that patients who took zinc gluconate lozenges got over their colds in 4.4 days on average, compared to 7.6 days for patients taking a placebo. The antizinc camp objects that the Cleveland study has fallen into the same trap as the Eby study — the subjects could tell which lozenges contained zinc, so their responses were biased. Were not, the Cleveland researchers riposte. But their conclusions are based mostly on the testees' personal assessment of their symptoms rather than on objective clinical measures, which doesn't give you much confidence.

Further complicating matters is the revelation that prior to publishing their study (but after completing their research) two Cleveland scientists bought stock in a company selling zinc lozenges. The stock of the company rose substantially when the study results were publicized.

So, am I skeptical? I'm always skeptical. There have been only a handful of zinc studies, involving small numbers of patients and yielding contradictory results. (Current score: four studies say it works, four say it doesn't.) A similar situation arose 20 years ago, only the cold cure in question was vitamin C. That controversy ended indecisively, and today you don't hear much about vitamin C as a cold cure. I'll bet you a jumbo box of Contac that the same thing happens to zinc.

Editor's note: Please see update of this column September 26, 2014.

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