Table 1:
Interventions for the prevention of the common cold
| Intervention | Formulation and dose | Evidence | Risk of bias | Outcome | Harms | Comment |
|---|---|---|---|---|---|---|
| Physical intervention30 | Various techniques (e.g., handwashing, use of alcohol-based hand disinfectant, gloves, masks) | Systematic review of 67 studies (various types) | High (studies had unclear risk of bias for most quality indicators) | General reduced risk with handwashing, hand disinfectant, gloves and masks | N95 masks offered no advantage over normal surgical masks, were uncomfortable and irritated the skin | Likely beneficial |
| Zinc supplement31–33 | Zinc sulfate tablets, 10 mg and 15 mg | Meta-analysis (2 RCTs; n = 400, age 5–8 yr) | High (unclear randomization;33 and events censored from analysis for unclear reasons32) | Pooled analysis of 2 RCTs: significant reduction in colds (RR 0.64, 95% CI 0.47 to 0.88); about 0.5–1.4 fewer colds over 5–7 “winter” months | 3 children in the intervention group in one RCT had mild gastrointestinal discomfort; no other significant differences noted | Likely beneficial |
| Probiotics34–36 | Different organisms, combinations, formulations and quantity; Lactobacillus most common (rhamnosus, casei and other species) | Systematic review and meta-analysis (10 RCTs; n = 3451), with focus on 2 RCTs of highest quality | Moderate (≤ 50% of the trials were low risk of bias for quality indicators) | Pooled analysis of 6 RCTs: significant reduction in number with ≥ 1 colds (OR 0.58, 95% CI 0.36 to 0.92); results of RCTs were inconsistent (I2 = 69%) | No difference noted | May be beneficial |
| Gargling37 | Tap water or diluted povidone–iodine (7%) solution, 20 mL gargled for 15 s 3 times per session; repeated at least 3 times daily | RCT (n = 384) | Low (allocation concealment and blinded outcome assessment) | Significantly fewer URTIs with gargling water (RR 0.64, 95% CI 0.42 to 0.99); no significant reduction with gargling povidone–iodine (RR 0.87, 95% CI 0.58 to 1.34) | Not reported | Unclear benefit from water gargling; no benefit from gargling of iodine solution |
| Ginseng38–40 | North American ginseng as COLD-FX brand in 5 of 6 RCTs (400 mg generally); Asian ginseng as Ginsana G115 brand | Systematic review (5 RCTs; n = 747) and single RCT (n = 783) | High (multiple variations of analysis) | Pooled analysis of 5 RCTs: no significant reduction in colds (relative risk 0.70, 95% CI 0.48 to 1.02); results of RCTs were inconsistent (I2 = 68%) Analysis of single RCT: no significant difference from placebo (p = 0.23) |
No consistent difference | Unclear benefit |
| Exercise41 | 45 min of moderate-intensity exercise 5 d/wk | RCT (n = 115 overweight or obese postmenopausal women) | High (unclear allocation concealment and equivocal findings) | Significantly fewer self-reported colds per person-year in intervention group (0.55 v. 0.96 in control group, p = 0.02); no difference in URTIs between groups (p = 0.16) | Not reported | Unclear benefit |
| Garlic supplement42,43 | Allicin powder 180 mg | Meta-analysis (1 RCT; n = 146) | High (1 trial had unclear allocation concealment) | 73 participants in each group; over 90-d period, 24 colds in intervention group v. 65 in control group (p < 0.001); unclear how many had no colds | Not reported (other than 4 taking garlic and 1 taking placebo having a smell when burping) | Unclear benefit |
| Homeopathy44–46 | Multiple different treatments | 3 RCTs (n = 170, 142 and 199 children, respectively, aged ≤ 10 yr) | Moderate (2 trials had 15%–23% drop out before first dose; 1 was nonblinded) | 2 placebo-controlled RCTs: no significant effect; 1 RCT with wait-list control showed reduced symptoms and days ill | 1 of 3 RCTs reported adverse events; 22% had mild and transient adverse effects, but control group not mentioned | Unclear (likely no) benefit |
| Vitamin C47 | Vitamin C 0.2–3 g/d (1 g/d most common) | Meta-analysis (29 RCTs; n = 11 306) | Unclear (reviewers used blinding as surrogate of allocation concealment) | Community participants: no effect (RR 0.97, 95% CI 0.94 to 1.00); participants exposed to cold or heavy physical stress: fewer colds (RR 0.48, 95% CI 0.35 to 0.64). Duration shorter than with placebo (mean difference −9.1%, 95% CI −12.6% to −5.6%). Effect not better with higher dose |
None reported | No benefit (no meaningful benefit in the average patient) |
| Vitamin D48,49 | Vitamin D 400 IU daily; 200 000 IU monthly for 2 mo, then 100 000 monthly | 2 RCTs (n = 164 male military recruits, 322 health workers or students) | Moderate (high risk of bias in one trial, low risk in the other trial) | No consistent benefit | Likely none | No benefit |
| Echinacea50 | Echinacea purpurea, E. angustifolia (pressed juice or extract in different dilutions and volumes) | Systematic review (2 RCTs; n = 519) | Low | 3 comparisons, not pooled: none showed statistical difference from placebo in preventing colds | No significant difference from placebo | No benefit |
Note: CI = confidence interval, OR = odds ratio, RCT = randomized control trial, RR = rate ratio, URTI = upper respiratory tract infection.