Subclinical Respiratory Impairment and Quality of Life Among Non-Smoking Adults in Rural Chiang Mai, Thailand

<b>Background</b>: Subclinical respiratory impairment among non-smokers in regions with haze-affected regions is still under-recognized, particularly in low- and middle-income countries (LMICs). This study assessed the prevalence of subclinical respiratory impairment among non-smoking adults and examined its determinants and associations with health-related quality of life (HRQoL) in Chiang Mai, Thailand. <b>Methods</b>: In this cross-sectional study, 244 non-smoking adults (18-65 years) from three rural districts underwent standardized spirometry and completed the Thai WHOQOL-BREF-26. Subclinical impairment was defined as an FEV₁/FVC < 0.70 or FVC < 80% predicted in the absence of symptoms. Demographic, occupational, and environmental information was obtained through structured questionnaires. Statistical analyses included non-parametric tests, univariate linear regression, and logistic regression. <b>Results</b>: A total of 37 participants (15.2%) had subclinical respiratory impairment. No demographic, occupational, or environmental factors such as sex, age, BMI category, agricultural work, marital status, and self-reported pollution exposure were found to be independently linked to impaired lung function. There was no correlation between spirometry indices and any WHOQOL-BREF domain. Elderly participants (>50 years) reported a higher level of physical and psychological HRQoL. Those with a higher Body Mass Index (BMI) were more likely to have a lower environmental quality of life. Farmers reported a better QoL, while women reported a lower QoL than men. <b>Conclusions</b>: Subclinical respiratory impairment occurs frequently in non-smoking rural adults exposed to haze pollution in Chiang Mai, and isn't presently assessed by general HRQoL instruments. These findings support early spirometry screening for asymptomatic adults in polluted regions, as well as more stringent air cleanliness strategies to prevent the evolution towards overt respiratory pathology.