However, taken as a whole, the evidence for the efficacy of zinc lozenges is inconclusive (Cochrane Database Syst Rev, 2000 : CD001364; J Nutr, 2000; 130 [5S Suppl]: 1512S-5S). The first study of zinc lozenges found a seven-day reduction in colds duration with zinc (Antimicrob Agents Chemother, 1984; 25: 20-4). Such results piqued drug company interest and, by the end of the1980s, five more studies had been carried out. However, only one of these showed zinc to have any effect. But then, in 1996, another study suggested that zinc lozenges were effective against cold symptoms (Ann Intern Med, 1996; 125: 81-8), thus launching zinc back on the road to popularity.
One trial of zinc lozenges (12.8 mg) found that patients taking one every two to three hours early in the course of a cold reduced the duration and severity of their symptoms, especially cough (Ann Intern Med, 2000; 133: 245-52).
But another randomised double-blind trial of 249 children (total daily dose of 50-60 mg) found no difference between zinc lozenges and placebo (J Am Med Assoc, 1998; 279: 1962-7). More recently, a trial of both zinc gluconate and zinc acetate concluded that neither had much effect on cold symptoms (Clin Infect Dis, 2000; 31: 1202-8).
So far, at least 10 double-blind trials have evaluated zinc lozenges for treating the common cold. Half have shown efficacy and half have not, results which may be due to methodological differences. Trials that began therapy shortly after onset of symptoms, used zinc gluconate or glycine-sweetened zinc gluconate and gave multiple daily zinc doses of 13-23 mg per dose found zinc to be effective. Most of the negative trials, on the other hand, varied from this protocol in one way or another.
Echinacea, one of the best-selling OTC herbals, has also shown mixed efficacy. German researchers gave the liquid root extract of either E. purpurea or E. angustifolia, two of the most popular types, or placebo to 302 healthy volunteers in a double-blind randomised trial. Results showed that both types of Echinacea were only slightly more effective than the placebo in preventing colds over a 12-week period, although participants taking the herb reported feeling better than those taking placebo. The authors concluded that, at best, Echinacea may reduce the risk of catching a cold by about 10-20 per cent (Arch Fam Med, 1998; 7: 541-5).
Other studies, however, have shown that Echinacea can relieve symptoms, reducing both the severity and duration of a cold (Arzneim Forsch, 2001; 51: 563-8; Arch Fam Med, 1998; 7: 541-5). One trial in Sweden looked at 246 healthy adults who caught a cold and took an E. purpurea preparation or placebo. The subjects took two tablets three times a day for seven days or until they felt better. The Echinacea preparations were significantly more effective than the placebo (Phytomedicine, 1999; 6: 1-6).
The key to these and other remedies may be to treat at the first signs of cold or flu. A recent review of 13 trials of Echinacea in the treatment and prevention of colds concluded that, while it may not prevent colds, early treatment could be beneficial for relieving symptoms (J Fam Pract, 1999; 48: 628-35). It also noted that Echinacea preparations vary widely in composition.
When colds or flu strikes, we all hope for a magic bullet to make things right, but most of the methods we use are still shots in the dark. Traditional approaches - usually involving rest, liquids and keeping warm - may not be glamorous but, in the end, appear to be effective, less prone to adverse effects and less expensive.