Serum Zinc Concentration in Relation to Asthma Control and Treatment-Step-Based Severity in Adults: A Retrospective Cross-Sectional Study

Background: Zinc supports immune homeostasis and participates in antioxidant defense and the regulation of inflammatory responses. Lower circulating zinc has been reported in asthma, mostly in children; its relation to disease control in adults is unclear. Objective: We examined serum zinc concentrations in relation to symptom control and treatment-defined disease severity in adults with asthma and whether any association with control was independent of potential confounders. Methods: In this retrospective cross-sectional study of 145 adults with asthma, serum zinc was compared between controlled (Asthma Control Test [ACT] > 19) and uncontrolled asthma and across treatment-step categories, using regression models adjusted for age, sex, C-reactive protein (CRP), smoking, and treatment step. Results: In the crude analysis, zinc was higher in controlled than in uncontrolled asthma (mean difference 6.7 µg/dL, 95% confidence interval [CI] 1.0 to 12.3), and zinc < 70 µg/dL was more frequent in uncontrolled asthma (18.6% vs. 5.8%). After full adjustment, these associations were attenuated and no longer statistically significant (mean difference 3.1 µg/dL, 95% CI −2.6 to 8.8). Zinc was lower at higher treatment steps in the unadjusted comparison (p = 0.0497), but this difference was not significant after adjustment for age (p = 0.277), and exploratory comparisons were imprecise. Conclusions: Higher serum zinc was associated with controlled asthma only in unadjusted analyses. These findings do not establish an independent or causal relationship, and whether zinc supplementation improves asthma control requires further study.