Zinc for the common cold

 

Abstract

Background

The common cold is one of the most widespread illnesses and is a leading cause of visits to the doctor and absenteeism from school and work. Trials conducted since 1984 investigating the role of zinc for the common cold symptoms have had mixed results. Inadequate treatment masking and reduced bioavailability of zinc from some formulations have been cited as influencing results.

Objectives

To assess the effect of zinc on common cold symptoms.

Search strategy

We searched CENTRAL (2010, Issue 2) which contains the Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to May week 3, 2010) and EMBASE (1974 to June 2010).

Selection criteria

Randomised, double-blind, placebo-controlled trials using zinc for at least five consecutive days to treat, or for at least five months to prevent the common cold.

Data collection and analysis

Two review authors independently extracted data and assessed trial quality.

Main results

We included 13 therapeutic trials (966 participants) and two preventive trials (394 participants). Intake of zinc is associated with a significant reduction in the duration (standardised mean difference (SMD) -0.97; 95% confidence interval (CI) -1.56 to -0.38) (P = 0.001), and severity of common cold symptoms (SMD -0.39; 95% CI -0.77 to -0.02) (P = 0.04). There was a significant difference between the zinc and control group for the proportion of participants symptomatic after seven days of treatment (OR 0.45; 95% CI 0.2 to 1.00) (P = 0.05). The incidence rate ratio (IRR) of developing a cold (IRR 0.64; 95% CI 0.47 to 0.88) (P = 0.006), school absence (P = 0.0003) and prescription of antibiotics (P < 0.00001) was lower in the zinc group. Overall adverse events (OR 1.59; 95% CI 0.97 to 2.58) (P = 0.06), bad taste (OR 2.64; 95% CI 1.91 to 3.64) (P < 0.00001) and nausea (OR 2.15; 95% CI 1.44 to 3.23) (P = 0.002) were higher in the zinc group.

Authors' conclusions

Zinc administered within 24 hours of onset of symptoms reduces the duration and severity of the common cold in healthy people. When supplemented for at least five months, it reduces cold incidence, school absenteeism and prescription of antibiotics in children. There is potential for zinc lozenges to produce side effects. In view of this and the differences in study populations, dosages, formulations and duration of treatment, it is difficult to make firm recommendations about the dose, formulation and duration that should be used.

 

Plain language summary

Zinc for the common cold

The common cold is often caused by the rhinovirus. It is one of the most widespread illnesses and is a leading cause of visits to the doctor and absenteeism from school and work. Complications of the common cold include otitis media (middle ear infection), sinusitis and exacerbations of reactive airway diseases. There is no proven treatment for the common cold. However, a medication that is even partially effective in the treatment and prevention of the common cold could markedly reduce morbidity and economic losses due to this illness.

Zinc inhibits rhinoviral replication and has been tested in trials for treatment of the common cold. This review identified 15 randomized controlled trials, enrolling 1360 participants of all age groups, comparing zinc with placebo (no zinc). We found that zinc (lozenges or syrup) is beneficial in reducing the duration and severity of the common cold in healthy people, when taken within 24 hours of onset of symptoms. People taking zinc are also less likely to have persistence of their cold symptoms beyond seven days of treatment. Zinc supplementation for at least five months reduces incidence, school absenteeism and prescription of antibiotics for children with the common cold. People taking zinc lozenges (not syrup or tablet form) are more likely to experience adverse events, including bad taste and nausea. As there are no studies in participants in whom common cold symptoms might be troublesome (for example, those with underlying chronic illness, immunodeficiency, asthma, etc.), the use of zinc currently cannot be recommended for them. Given the variability in the populations studied (no studies from low- or middle-income countries), dose, formulation and duration of zinc used in the included studies, more research is needed to address these variabilities and determine the optimal duration of treatment as well as the dosage and formulations of zinc that will produce clinical benefits without increasing adverse effects, before making a general recommendation for zinc in treatment of the common cold.

 

Resumen

Antecedentes

Zinc para el resfriado común

El resfriado común es una de las enfermedades más difundidas, y es una causa principal de consultas médicas y absentismo escolar y laboral. Los ensayos realizados desde 1984 que investigan la función del zinc en cuanto a los síntomas de resfriado común han tenido resultados contradictorios. Se ha planteado que en los resultados presentados han influido el enmascaramiento inadecuado del tratamiento y la escasa biodisponibilidad del zinc de algunas formulaciones.

Objetivos

Evaluar el efecto del zinc sobre los síntomas de resfriado común.

Estrategia de búsqueda

Se hicieron búsquedas en CENTRAL (2010, número 2) que incluye el Registro Especializado de Ensayos Controlados del Grupo Cochrane de Infecciones Respiratorias Agudas (Acute Respiratory Infections Group), MEDLINE (1966 hasta mayo, semana 3, 2010) y EMBASE (1974 hasta junio 2010).

Criterios de selección

Ensayos con asignación aleatoria, doble ciego, controlados con placebo que utilizaran zinc durante al menos cinco días consecutivos para el tratamiento, o durante al menos cinco meses para la prevención del resfriado común.

Obtención y análisis de los datos

Dos autores de la revisión extrajeron los datos de forma independiente y evaluaron la calidad de los ensayos.

Resultados principales

Se incluyeron 13 ensayos terapéuticos (966 participantes) y dos ensayos preventivos (394 participantes). La ingesta de zinc se asocia con una reducción significativa de la duración (diferencia de medias estandarizada [DME] −0,97; intervalo de confianza [IC] del 95%: −1,56 a −0,38) (p = 0,001) y la gravedad de los síntomas de resfriado común (DME −0,39; IC del 95%: −0,77 a −0,02) (p = 0,04). Hubo una diferencia significativa entre el grupo de zinc y de control en cuanto a la proporción de participantes sintomáticos después de siete días de tratamiento (OR 0,45; IC del 95%: 0,2 a 1,00) (p = 0,05). El cociente de tasas de incidencia (CTI) de la aparición de un resfriado (CTI 0,64; IC del 95%: 0,47 a 0,88) (p = 0,006), del absentismo escolar (p = 0,0003) y de la prescripción de antibióticos (p < 0,00001) fue inferior en el grupo de zinc. Los eventos adversos generales (OR: 1,59; IC del 95%: 0,97 a 2,58) (p = 0,06), sabor desagradable (OR 2,64; IC del 95%: 1,91 a 3,64) (p < 0,00001) y náuseas (OR 2,15; IC del 95%: 1,44 a 3,23) (p = 0,002) fueron mayores en el grupo de zinc.

Conclusiones de los autores

El zinc administrado en el plazo de las 24 horas posteriores a la aparición de los síntomas reduce la duración y la gravedad del resfriado común en las personas sanas. Cuando se administra durante al menos cinco meses, reduce la incidencia del resfriado, el absentismo escolar y la prescripción de antibióticos en los niños. Existe la posibilidad de efectos secundarios con las tabletas de zinc. Al considerar este hecho y las diferencias en las poblaciones de estudio, las dosificaciones, las formulaciones y la duración del tratamiento, es difícil realizar recomendaciones firmes acerca de la dosis, la formulación y la duración que deben utilizarse.

Traducción

Traducción realizada por el Centro Cochrane Iberoamericano