<b>Impact of Glycemic Control on Asthma Exacerbation, Asthma Control, and Lung Function in Diabetic Patients: A Systematic Review</b>

Background: Asthma and diabetes mellitus frequently coexist and may interact through metabolic and inflammatory pathways that influence exacerbation risk and pulmonary function. Glycemic dysregulation has been proposed as a contributor to poorer asthma outcomes, yet the clinical evidence has not been consistently synthesized across outcome domains. Objective: To systematically evaluate the impact of glycemic control on asthma exacerbations, asthma control, asthma-related healthcare utilization, and lung function in individuals with asthma and diabetes mellitus or glycemic dysfunction. Methods: A PRISMA-compliant systematic review was conducted using PubMed/MEDLINE, Scopus, Web of Science, and Google Scholar to identify original observational and interventional studies published through March 2025. Eligible studies assessed glycemic status using HbA1c and/or blood glucose indices and reported asthma-related outcomes including exacerbations, emergency department visits, hospitalization, asthma control measures, and spirometric parameters (FEV₁, FVC, vital capacity). Methodological quality was assessed using the Newcastle–Ottawa Scale. Due to heterogeneity in exposure definitions, outcomes, and effect reporting, findings were synthesized narratively. Results: Five studies met inclusion criteria. Across studies, poorer glycemic control was generally associated with lower lung function and increased risk of asthma-related hospitalization. Higher HbA1c correlated inversely with spirometric indices, including FEV₁ and FVC. Population-based evidence indicated elevated HbA1c, including levels in prediabetes and diabetes ranges, was associated with higher odds of asthma-related hospitalization. Metformin exposure was associated with reduced hazards of asthma-related emergency department visits and hospitalization in a large retrospective cohort. Conclusion: Poor glycemic status is associated with increased asthma morbidity and reduced lung function. Optimizing glycemic control may be clinically relevant in integrated asthma–diabetes management, although higher-quality prospective studies and trials are needed to establish causality.