Associations of Cardiorespiratory Fitness and Body Mass Index with Incident Restrictive Spirometry Pattern

OBJECTIVES: Restrictive spirometry pattern suggests an impairment of lung function associated with a significantly increased risk of premature mortality. We evaluated the independent and joint associations of cardiorespiratory fitness and body mass index with incident restrictive spirometry pattern. METHODS: Data from the Aerobics Center Longitudinal Study included 12,360 participants (18–82 years). CRF was assessed by maximal treadmill test and categorized into five groups. Body mass index was categorized into normal weight (<25.0 kg/m(2)), overweight (25.0–29.9 kg/m(2)), or obesity (≥30.0 kg/m(2)). Restrictive spirometry pattern was defined as the simultaneous occurrence of forced expiratory volume in 1-second/force vital capacity ≥ lower limit of normal and forced vital capacity < lower limit of normal. RESULTS: There were 900 (7.3%) cases of restrictive spirometry pattern (mean follow-up: 6.9 years). Compared to ‘category 1 (least fit),’ hazard ratios (HRs) (95% confidence intervals *CIs+) of RSP were 0.78 (0.63–0.96), 0.68 (0.54–0.86), 0.70 (0.55–0.88), and 0.59 (0.45–0.77) in categories 2, 3, 4, and 5 (most fit), respectively, after adjusting for confounders including body mass index. Compared to normal weight, HRs (95% CIs) of RSP were 1.06 (0.91–1.23) and 1.30 (1.03–1.64) in overweight and obese, respectively. However, the association between obesity and restrictive spirometry pattern was attenuated when additionally adjusting for cardiorespiratory fitness (HR: 1.08, 95% CI: 0.84–1.39). Compared to the ‘unfit and overweight/obese’ group, HRs (95% CIs) for restrictive spirometry pattern were 1.35 (0.98–1.85), 0.77 (0.63–0.96), and 0.70 (0.56–0.87) in the ‘unfit and normal weight,’ ‘fit and overweight/obese,’ and ‘fit and normal weight’ groups, respectively. CONCLUSIONS: Low cardiorespiratory fitness was associated with a greater incidence of restrictive spirometry pattern, irrespective of body mass index. Future studies are needed to explore potential underlying mechanisms of this association and to prospectively evaluate if improving cardiorespiratory fitness reduces the risk of developing restrictive spirometry pattern.