Efficacy of Normalising Serum Zinc Level for Patients with Olfactory Dysfunction and Zinc Deficiency

Abstract

<b><i>Introduction:</i></b> Zinc deficiency may worsen the severity of olfactory dysfunction; however, the relationship between serum zinc levels and therapeutic effects on olfactory dysfunction remains uncertain. This study investigated the relationship between normalising serum zinc levels and the therapeutic effects on olfactory dysfunction. <b><i>Methods:</i></b> Forty-two patients diagnosed with post-infectious, post-traumatic, and idiopathic olfactory dysfunction, with serum zinc levels &lt;70 μg/dL, were included in the study. All patients were treated with mecobalamin, tokishakuyakusan, and polaprezinc. The patients were divided into 2 groups: the zinc-normalised (≥70 μg/dL) and zinc-deficient (&lt;70 μg/dL) groups, based on their post-treatment serum zinc levels. Olfactory test results were compared in each of the 2 groups. <b><i>Results:</i></b> The patients were treated for a median of 133 days. The zinc-normalised group had significantly better results in all olfactory tests (detection/recognition thresholds of the T&amp;T olfactometer, odour identification test (Open Essence), Visual Analogue Scale for olfactory dysfunction, and self-administered odour questionnaire). In contrast, only the self-administered odour questionnaire showed a significant improvement in the zinc-deficient group, with no significant differences observed in the other olfactory tests. When comparing the changes in the olfactory test scores between the 2 groups, significant differences were observed in the detection/recognition thresholds of the T&amp;T olfactometer test and Open Essence results. <b><i>Conclusion:</i></b> These findings suggest that patients with olfactory dysfunction may have difficulty improving their olfactory function if they also have zinc deficiency. Furthermore, normalisation of zinc deficiency may contribute to the improvement of olfactory dysfunction with general treatment.