Lifetime Body Mass Index Trajectories and Contrasting Lung Function Abnormalities in Mid‐Adulthood: Data From the Tasmanian Longitudinal Health Study

ABSTRACT Background and Objective The impact of lifetime body mass index (BMI) trajectories on adult lung function abnormalities has not been investigated previously. We investigated associations of BMI trajectories from childhood to mid‐adulthood with lung function deficits and COPD in mid‐adulthood. Methods Five BMI trajectories ( n = 4194) from age 5 to 43 were identified in the Tasmanian Longitudinal Health Study. Lung function outcomes were defined using spirometry at 45 and 53 years. Associations between these BMI trajectories and lung function outcomes were investigated using multivariable regression. Results Compared to the average BMI trajectory, the child's average‐increasing BMI trajectory was associated with greater FVC decline from 45 to 53 years (β = −178 mL; 95% CI −300.6, −55.4), lower FRC, ERV and higher TLco at 45 years, lower FVC (−227 mL; −345.3, −109.1) and higher TLco at 53 years. The High BMI trajectory was also associated with lower FRC, ERV and higher TLco at 45 years, while spirometric restriction (OR = 6.9; 2.3, 21.1) and higher TLco at 53 years. The low BMI trajectory was associated with an obstructive picture: lower FEV 1 (−124 mL; −196.4, −51.4) and FVC (−91 mL; −173.4, −7.7), and FEV 1 /FVC (−1.2%; −2.2, −0.1) and higher ERV and lower TLco at 45 and 53 years. A similar pattern was found at 53 years. No associations were observed with spirometrically defined COPD. Conclusion Our findings revealed contrasting lung function abnormalities were associated with high, subsequently increasing, and low BMI trajectories. These results emphasise the importance of tracking changes in BMI over time and the need to maintain an average BMI trajectory (BMI‐Z‐score 0 at each time point) throughout life.