Abstract
- Background
The common cold is an acute, self-limiting viral respiratory illness that imposes a heavy public health burden, leading to significant absenteeism from work and school. While no definitive interventions exist to prevent colds or shorten their duration, zinc supplements are widely used for this purpose. This Cochrane review systematically evaluated the effectiveness and safety of zinc supplementation for preventing and treating the common cold.
- Methods
Randomized controlled trials ($\text{RCTs}$) testing mono-zinc interventions against placebo in children or adults were identified across major databases (CENTRAL, MEDLINE, Embase, CINAHL, LILACS, Web of Science, and trials registries to June 2023). Trials evaluating zinc in combination with other minerals, vitamins, or herbs were excluded. Primary outcomes evaluated included cold incidence (prevention trials), cold duration in days, treatment-emergent non-serious and serious adverse events, and potential cold-related complications. Study quality and evidence certainty were evaluated using the Cochrane Risk of Bias tool and GRADE assessment, respectively.
- Results
A total of 34 studies (15 prevention, 19 treatment) involving 8,526 participants were included (22 adult studies, 12 pediatric studies). Most trials (17/34) evaluated zinc lozenges (acetate, gluconate, or orotate forms). Dosing for zinc gluconate ranged between 45 and 276 mg/day over 4.5 to 21 days.
Prevention: Zinc supplementation showed little to no effect on reducing the risk of developing a cold ({RR}: 0.93- 95\ CI}: $0.85, 1.01$; $I^2 = 20\%$; 9 studies; low-certainty evidence) or the mean number of colds over 5 to 18 months of follow-up {MD}-0.90days $95\{ CI}$: $-1.93, 0.12$; 2 studies; low-certainty evidence). When colds did occur during prevention trials, there was probably little to no difference in cold duration MD-0.63\days} 95\%\{ CI}$: $-1.29, 0.04$; 3 studies; moderate-certainty evidence) or global symptom severity SMD}$: $0.04$; $95 CI}$: $-0.35, 0.43$; 2 studies; low-certainty evidence).
Treatment: For cold treatment, zinc supplementation may reduce the mean duration of colds by approximately 2.37 days ({MD}$: $-2.37\{ days} 95\%\CI}$: $-4.21, -0.53$; $I^2 = 97\%$; 8 studies; low-certainty evidence). However, its effect on reducing the risk of an ongoing cold at follow-up (RR}$: $0.52$; $95\ CI}$: $0.21, 1.27$; 5 studies; very low-certainty evidence) or global symptom severity ({SMD}$: $-0.03$; $95\%CI}$: $-0.56, 0.50$; 2 studies; very low-certainty evidence) remains uncertain.
Safety: Non-serious adverse events were reported in 31 studies (2,422 participants). The risk of adverse events during prevention trials remains uncertain (RR}$: $1.11$; $95\%\CI}$: $0.84, 1.47$; very low-certainty evidence). However, using zinc for cold treatment probably increases the risk of non-serious adverse events ($R}$: $1.34$; $95\% CI}$: $1.15, 1.55$; $I^2 = 44\%$; 16 studies; moderate-certainty evidence). No treatment studies provided clear data on serious adverse events or cold-related complications.
- Conclusions
Zinc supplementation appears to offer little to no benefit for cold prevention. However, when used as a therapeutic intervention for acute illness, zinc may shorten the mean duration of cold symptoms by over two days, albeit with a higher incidence of non-serious adverse events. High heterogeneity and incomplete reporting across studies warrant cautious interpretation of these findings.
https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.cd014914.pub2/full