Prevention trials. In one prevention trial, which included only children ages 6½ to 10 years, those in the intervention group took one 10-mg zinc sulfate tablet 6 days a week for 5 months. In the other trial, children in the intervention group took 15 mg zinc sulfate syrup daily for 7 months.
Pooled results from these 2 studies revealed that daily zinc supplementation substantially reduced the incidence of colds. The incident rate ratio (the number of children who developed colds while taking zinc compared with the number who developed colds while on placebo) was 0.64 (95% CI, 0.47-0.88). In the original trials, one study found a difference of 0.5 colds (1.7 in the control group vs 1.2 in the intervention group) per season, and the other found a difference of 1.8 colds per season (3.15 in the control group vs 1.37 in the intervention group).
WHAT’s NEW: Evidence of zinc’s cold relief properties is conclusive
This Cochrane review provides convincing evidence from 13 randomized placebo-controlled trials that taking zinc soon after the onset of symptoms of the common cold significantly reduces both the duration and severity of symptoms. Zinc supplements are widely available over the counter, so you can recommend that patients take zinc the next time they develop a cold.
In addition, 2 prevention trials found that zinc can reduce the incidence of colds in children, whether it is taken as a syrup or in tablet form. There have been few trials of zinc for prophylaxis of the common cold, and no previous meta-analyses included preventive studies.7 This Cochrane review substantiates the effectiveness of zinc for prophylaxis of the common cold in young children.
However, children need to take zinc daily for prophylaxis, which may be inconvenient. Long-term safety information is not yet available. Given these considerations, parents may choose to wait for additional evidence about safety before considering daily prophylaxis.
CAVEATS: Adverse effects, long-term use may create problems
In this meta-analysis, side effects from zinc were common. The 2 most frequently reported were bad taste (pooled odds ratio [OR], 2.64; 95% CI, 1.91-3.64) and nausea (pooled OR, 2.15; 95% CI, 1.44-3.23). When you recommend zinc, warn your patients about these adverse effects. The side effects are not severe, so patients can decide for themselves whether the benefit of a reduction in cold duration is worth the downside of nausea and a bad taste in the mouth.
It is also important to note that the trials included in the meta-analysis enrolled healthy children and adults ≤65 years old. Whether zinc benefits people with chronic illnesses (eg, chronic obstructive pulmonary disease) who develop colds is unknown.
Prolonged elevated serum zinc levels can interfere with copper metabolism, and the adverse effects of long-term use of zinc as prophylaxis are unknown. The trials included in the meta-analysis took place in relatively affluent countries in which zinc deficiency is uncommon. It is not known what impact zinc supplementation would have on people in poor countries.
Of the 15 studies included in the meta-analysis, 10 received support from pharmaceutical companies, 4 received support from foundations, and one received support from both.
CHALLENGES TO IMPLEMENTATION: When to talk to patients about zinc
Most patients do not seek medical care for colds. Those who do typically present only after having symptoms for several days, and it is not clear whether zinc supplementation has the same beneficial effects when started after the first 24 hours.2
Thus, you may have few opportunities in the office to recommend zinc for patients with colds, for whom there is evidence of immediate benefit. More likely, you’ll need to incorporate a zinc recommendation into your overall advice about colds.
Zinc is available over the counter in various forms and dosage. After recommending zinc, you may be confronted with the question of which dose, brand, and formulation is best—a question which, unfortunately, remains unanswered.
Acknowledgement
The PURLs Surveillance System is supported in part by Grant Number UL1RR024999 from the National Center For Research Resources, a Clinical Translational Science Award to the University of Chicago. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center for Research Resources or the National Institutes of Health.