Prevalence of Asymptomatic Bronchial Hyperresponsiveness in Indian Adolescents: Insights From the APEAL Study.

Background: Bronchial hyperresponsiveness (BHR), often undetected in asymptomatic individuals, may represent an early marker of airway inflammation and a precursor to chronic respiratory disease (CRD). Despite its established role in asthma and COPD, BHR remains under-recognised in epidemiologic screenings, particularly in low- and middle-income countries like India, where environmental exposures are high.

Objective: This study assessed the prevalence and burden of asymptomatic BHR in adolescents across four Indian cities: Mysuru, Bengaluru, Mumbai and Delhi, using objective airway reversibility measures.

Methods: This secondary analysis of the APEAL study (Air Pollution Exposure on Adolescents' Lungs) included 4141 randomly selected adolescents (11-14 years) with no reported respiratory symptoms or prior physician diagnosis of asthma. Pulmonary function tests (PFTs) assessed forced expiratory volume in 1 s (FEV₁) pre- and post-bronchodilator. BHR was defined as post-bronchodilator increase in FEV₁ of ≥ 12% and ≥ 200 mL. Anthropometric, socioeconomic and environmental factors were analysed.

Results: A total of 165 adolescents (4.0%) met criteria for asymptomatic BHR, with site-wise variation: Mumbai (5.6%), Delhi (4.5%), Bengaluru (4.2%) and Mysuru (2.3%). Males predominated except in Delhi. Younger age was significantly associated with BHR (OR = 1.48; p = 0.035). A dose-dependent association with PM_2.5 was observed: 64.1-124.8 μg/m³ increased BHR risk (OR = 1.83; p = 0.033), with higher risk above 124.8 μg/m³ (OR = 2.56; p = 0.003). In GLM analysis, Mumbai residents had lower odds of moderate (Estimate = -1.757, p = 0.048) and severe airflow limitation (Estimate = -3.200, p = 0.022) than Bengaluru. Underweight status was associated with increased risk of severe airflow limitation (Estimate =2.073, p = 0.048), while overweight appeared protective (Estimate = -14.357; p < 0.001). Obesity had similar estimates (2.075) as underweight but was non-significant due to a smaller number of subjects.

Conclusion: Asymptomatic BHR affects a substantial proportion of urban Indian adolescents and is associated with age, undernutrition and PM_2.5 exposure. Symptom-based screening may miss early airway abnormalities. School-based spirometry screening could aid in early identification of BHR and reduce long-term CRD risk.