The effects of zinc supplementation on olfactory disorders: a systematic review with meta-analysis

OBJECTIVES: This systematic review aimed to evaluate the efficacy of zinc supplementation for treating olfactory disorders, including quantitative and qualitative symptoms, in adults. METHODS: We conducted a comprehensive search of the Cochrane Central Register of Controlled Trials, Pubmed, Embase, and other relevant databases for Randomized Controlled Trials (RCTs) and observational studies evaluating zinc supplementation for olfactory dysfunction. Studies published up to April 2025 were included. Improvement in olfactory function was assessed with validated olfactory tests or subjective questionnaires. Qualitative symptoms (parosmia, phantosmia), adverse effects, patient-reported outcomes, and quality of life measured by questionnaires were evaluated. RESULTS: A total of 6 studies, including 3 RCTs and 3 observational studies, were included in the review. Sample sizes varied between 25 and 606 participants, with follow-up durations ranging from 1 to 15 months. The meta-analysis showed no significant difference in olfactory function improvement between the zinc-treated group and the control group (OR = 1.78; 95% CI 0.63-5.03; p = 0.28). In addition, the analysis of subjective perception of improvement, also did not demonstrate a statistically significant effect (OR = 0.69; 95% CI 0.25-1.93; p = 0.48). However, an individual study reported improvement in specific subgroups, such as those with posttraumatic anosmia. Adverse events were generally mild and primarily gastrointestinal. CONCLUSION: Current evidence does not support a clear benefit of zinc supplementation for olfactory disorders. Further high-quality RCTs are necessary to determine its potential role, particularly in targeted subgroups. LEVEL OF EVIDENCE: Level 2a.