Zinc has become the hot new therapy for the common cold. Once just a weak-selling natural cold remedy touted in health-food stores, it now sells to millions at pharmacies and grocery stores. Does it work? Probably not. Does it sell? Ask the big pharmaceutical companies whose immense resources are nurturing the all-too-credulous market for unproven alternative medicines.
Zinc, a nutrient found in red meat, is known to be essential to growth and immune-system function. It was not plugged as a cold remedy, however, until 1979, when a Texas city planner, George Eby, became convinced that megadoses of zinc improved his 3-year-old leukemic daughter's response to chemotherapy and protected her from colds during treatment. While such anecdotes commonly spur alternative-medicine fads, Eby took the admirable step of instigating a 1984 clinical trial of zinc lozenges that found the treatment cut the duration of colds in half.
Zinc did not really sell, however, until the summer of 1996, when the Annals of Internal Medicine published a Cleveland Clinic study with similar results. Patients showing cold symptoms for 24 hours or less were given either zinc or placebo lozenges. They were instructed to dissolve one lozenge in their mouths every two hours while awake, until the symptoms were gone. Symptoms in zinc takers disappeared after 4.4 days, compared with 7.6 days for those in the placebo group. The only problem was zinc's bitter taste. Eighty percent of patients who got zinc complained of a bad aftertaste, and 20 percent felt nauseated.
Still, the evidence for zinc is equivocal. Eby's initial trial stimulated seven other studies, and while three found zinc worked, four found it did not. Army researchers in Tacoma, Wash., recently pooled the zinc data for a comprehensive "meta-analysis," published last month in the Archives of Internal Medicine. They found no benefit, concluding, "The evidence for effectiveness of zinc salts lozenges in reducing the duration of common colds is still lacking." It is also unknown whether large doses of zinc have toxic effects in the long run.
Some scientists question whether it is even biologically plausible that zinc could cure colds. Zinc backers propose that the element's positive charge could a) bind it to viruses, blocking their entry into the cells along your nasal tract or b) allow it to "clamp" nerves that stimulate congestion. However, University of Virginia researcher Jack Gwaltney pointed out that zinc in the saliva does not reach the nasal tract, and therefore cannot exert any of these effects. Furthermore, the zinc levels needed to kill cold viruses in the test tube are far higher than anything the lozenges achieve.
Gwaltney and others believe a placebo effect may account for the sporadic positive results from zinc. It is known that inert substances can alleviate symptoms in colds, asthma, sciatica, and even congestive heart failure through the power of suggestion alone. This is not to say the symptoms are just in the mind, but rather that the mind can generate beneficial biological effects. You might think that the fact that zinc beat the placebo in the Cleveland Clinic trial would rule out a placebo effect. But a dummy pill only works as much as you believe in it. Belief can be affected by many factors, including the drug's appearance (certain pill colors are more effective than others), form (injections often have a greater effect than pills), or taste (bitter may seem like better).
The zinc trials did not, for example, mask zinc's bitter, medicine-like flavor. Zinc may work primarily because its distinctive taste helps convince you that it will. This phenomenon has long confounded research on vitamin C, which, after almost two-dozen studies, has not been demonstrated to provide benefit in colds beyond its placebo effect.
Nonetheless, publicity from the Cleveland Clinic trial made the Quigley Corp.'s Cold-Eeze zinc gluconate lozenges a runaway success. Quigley was a struggling dietary-supplement company prior to the study: It's stock sold for less than a dollar a share, and revenues for the first half of 1996 were just under $175,000. The study's release boosted the stock to $37 a share overnight and has generated $41 million in revenues in the year since.
Subsequent revelations that the trial's lead researcher owned stock in Quigley raised questions of biased results. On the day that his article was published, Dr. Michael Macknin sold 9,000 Quigley shares for $145,000 in profit. During the course of the study, Quigley gave Macknin options for an additional 10,000 shares. According to the Cleveland Plain Dealer, however, Macknin denied that this was a payment and said he received the options after his results had already been compiled.
Others soon joined the zinc rush. Nu-Wave Health Product introduced Cold-Rid sugar-free zinc lozenges. Weider Nutrition International offers Cold-Free zinc acetate lozenges, which it claims have higher zinc concentrations. There is zinc gum, zinc spray, even zinc lollipops. And now pharmaceutical giant Warner-Lambert has jumped in with Hall's Zinc Defense, a lozenge backed by a national TV-ad campaign.