Table 1:

Interventions for the prevention of the common cold

InterventionFormulation and doseEvidenceRisk of biasOutcomeHarmsComment
Physical intervention30Various 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 masksN95 masks offered no advantage over normal surgical masks, were uncomfortable and irritated the skinLikely beneficial
Zinc supplement3133Zinc sulfate tablets, 10 mg and 15 mgMeta-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” months3 children in the intervention group in one RCT had mild gastrointestinal discomfort; no other significant differences notedLikely beneficial
Probiotics3436Different 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 qualityModerate (≤ 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 notedMay be beneficial
Gargling37Tap water or diluted povidone–iodine (7%) solution, 20 mL gargled for 15 s 3 times per session; repeated at least 3 times dailyRCT (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 reportedUnclear benefit from water gargling; no benefit from gargling of iodine solution
Ginseng3840North American ginseng as COLD-FX brand in 5 of 6 RCTs (400 mg generally); Asian ginseng as Ginsana G115 brandSystematic 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 differenceUnclear benefit
Exercise4145 min of moderate-intensity exercise 5 d/wkRCT (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 reportedUnclear benefit
Garlic supplement42,43Allicin powder 180 mgMeta-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 coldsNot reported (other than 4 taking garlic and 1 taking placebo having a smell when burping)Unclear benefit
Homeopathy4446Multiple different treatments3 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 ill1 of 3 RCTs reported adverse events; 22% had mild and transient adverse effects, but control group not mentionedUnclear (likely no) benefit
Vitamin C47Vitamin 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 reportedNo benefit (no meaningful benefit in the average patient)
Vitamin D48,49Vitamin D 400 IU daily; 200 000 IU monthly for 2 mo, then 100 000 monthly2 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 benefitLikely noneNo benefit
Echinacea50Echinacea purpurea, E. angustifolia (pressed juice or extract in different dilutions and volumes)Systematic review (2 RCTs; n = 519)Low3 comparisons, not pooled: none showed statistical difference from placebo in preventing coldsNo significant difference from placeboNo benefit
  • Note: CI = confidence interval, OR = odds ratio, RCT = randomized control trial, RR = rate ratio, URTI = upper respiratory tract infection.