Evidence for Zinc Use in Upper Respiratory Tract Infections
Zinc administered as zinc gluconate lozenges at a dose of ≥75 mg/day and taken within 24 hours of symptom onset significantly reduces the duration of common cold symptoms by approximately 2.5-3 days. 1, 2
Efficacy of Zinc in URTIs
Mechanism and Evidence
- Zinc has demonstrated antiviral properties and plays a role in immune regulation in the respiratory tract 3
- According to the European Position Paper on Rhinosinusitis and Nasal Polyps 2020, zinc lozenges can significantly reduce the duration of common cold when:
- Administered as zinc acetate or zinc gluconate
- Given at doses of ≥75 mg/day
- Started within 24 hours of symptom onset 1
Formulation and Delivery Method
- Lozenges appear to be the most effective delivery method for treating common cold symptoms 2
- Recommended dosage: 13.3-23 mg per lozenge taken every 2 hours 2
- Other formulations show less consistent results:
Clinical Application
When to Use Zinc
- Start zinc supplementation within 24 hours of symptom onset for maximum benefit 1, 2
- Continue throughout the duration of the cold 1
- Most beneficial for adults with established common cold symptoms 2
Dosing Recommendations
- For treating common cold in adults: 75 mg/day of elemental zinc as zinc gluconate 2
- For children: 75 mg/day in three divided doses for those under 50 kg 2
Limitations and Contradictions in Evidence
- Evidence is conflicting regarding zinc's efficacy:
- The American College of Physicians and CDC note that "because of conflicting data, it is not clear whether zinc-containing compounds are beneficial in treating cough due to the common cold" 1
- The ACCP Evidence-Based Clinical Practice Guidelines also mention conflicting data on zinc's benefit 1
- Some studies show no clinically significant reduction in symptoms 7
Adverse Effects and Precautions
Common Side Effects
- Nausea and altered taste reported by up to 50% of subjects in some studies 7
- Gastric irritation is common 2
- These adverse effects are generally well-tolerated and self-limiting 2
Contraindications
- Zinc is not recommended for treating isolated sore throat as a standalone therapy (evidence rating B-2) 1
- Potential for zinc toxicity with excessive administration, which can lead to copper deficiency 2
Special Considerations
Preventive Use
- Currently, no firm recommendation can be made for prophylactic zinc supplementation due to insufficient data 1
- Some evidence suggests zinc combined with vitamin A may reduce URTI morbidity in children with marginal nutritional status 6
Combination Therapy
- Zinc is typically used as a standalone treatment for common cold symptoms
- No strong evidence supports combining zinc with other treatments for enhanced efficacy in URTIs
Bottom Line
Zinc gluconate lozenges at doses of ≥75 mg/day started within 24 hours of symptom onset can reduce the duration of common cold symptoms by 2.5-3 days. However, the benefits must be weighed against potential adverse effects like nausea and altered taste. The evidence is strongest for the lozenge formulation, while other delivery methods show less consistent results.