Glycated Hemoglobin A_1c, Lung Function, and Hospitalizations Among Adults with Asthma

Insulin resistance and metabolic dysfunction have been associated with asthma risk and asthma severity.

To examine the association between glycated hemoglobin A_1c (HbA_1c), asthma-related hospitalizations, and lung function measures among adults in the United Kingdom.

A cross-sectional study was conducted of 47,606 adults aged 40 to 69 years who participated in the UK Biobank and had asthma but no diagnosis of diabetes mellitus. HbA_1c level was analyzed as a continuous measure and also categorized as normal (<42 mmol/mol) or as consistent with prediabetes/diabetes (≥42 mmol/mol). An asthma-related hospitalization was defined as ever having had a hospitalization with an International Classification of Diseases, Ninth/Tenth Revision, Clinical Modification code of a main diagnosis compatible with asthma (International Classification of Diseases, Ninth Revision, Clinical Modification code 493.x or International Classification of Diseases, Tenth Revision, Clinical Modification codes J45.x and J46.x). Logistic or linear regression was used for the multivariable analysis of asthma hospitalizations and lung function measures (FEV₁, forced vital capacity [FVC], and FEV₁/FVC). All models were adjusted for age, sex, ethnic background, body mass index, average annual household income, current smoking status, pack-years of smoking, fasting time, and C-reactive protein level.

Both HbA_1c level (odds ratio, 1.03; 95% CI, 1.01-1.04) and an HbA_1c level in the prediabetes/diabetes range (odds ratio, 1.68; 95% CI, 1.18-2.41) were associated with 1 or more asthma hospitalizations. Moreover, both HbA_1c level and an HbA_1c level in the prediabetes/diabetes range were significantly and inversely associated with FEV₁ and FVC.

HbA_1c is linked to asthma-related hospitalizations and small decrements in FEV₁ and FVC among British adults with asthma but no diagnosis of diabetes mellitus.