Determinants of Lung Function at Age 8.5 Years in a Birth Cohort of Thai Children

Background and aims: Early life factors have reported the associations with impaired lung function in later life. In the present study, the birth cohort was followed up longitudinally to investigate the determinants of lung function in Thai children. Methods: Cohort subjects were recruited from children born in Songkhla Province in southern Thailand. Data collections were obtained starting from antenatal, at birth, and at 1, 5 and 8.5 years of age. Spirometry was assessed at age 8.5 years. The variables investigated included birth weight, smoke exposure, respiratory diseases during the newborn period and during the first year of life, and asthma diagnosed at age 5 or 8.5 years. Results: Of 1056 subjects, 892 (84.5%) subjects completed the spirometric measurements. The presence of asthma was the only factor that was significantly associated with a lower forced expiratory volume in 1s (FEV1)/forced vital capacity (FVC) ratio, forced expiratory flow at 25-75% vital capacity (FEF25-75%VC) and peak expiratory flow rate (PEFR). The regression analysis found that asthma was significantly associated with a lower FEV1/FVC ratio, FEF25-75%VC, and PEFR value with estimated coefficients +/- standard error of -1.27 +/- 0.55%, p = 0.02; -131.8 +/- 48.2 ml/s, p = 0.006; and -166.2 +/- 65.0 ml/s, p = 0.01, respectively. Asthma diagnosed at age 5 or 8.5 years was more likely among children who had lower respiratory tract illness during the first year of life. The odds ratio for the association was 4.81 (95% confidence interval 2.14-10.83, p < 0.001). Conclusion: The main factor associated with lower lung function in Thai cohort subjects was the present of asthma by age 5 or 8.5 years and early respiratory illness was the risk factor for asthma in childhood period.