Midlife cardiorespiratory fitness and the long-term risk of chronic obstructive pulmonary disease
Hansen GM, Marott JL, Holtermann A, et al.
Chronic obstructive pulmonary disease (COPD) is caused by gradual destruction of the airways and alveoli, typically due to the inhalation of harmful gases and particles. Regular physical activity is associated with a reduced risk of COPD, however, due to the progressive nature of COPD, very long follow-up is required when studying the links between physical activity and COPD to minimise bias from reverse causation (i.e. the measured physical fitness parameter is affected by subclinical disease present at the start of follow-up). In addition to short follow-up timescales, previous studies have relied on self-report measures of physical activity, which can be subjective and prone to overreporting.
Hansen and colleagues set out to examine the association between midlife cardiorespiratory fitness (CRF) and long-term risk of COPD and COPD-related mortality.
In this study, employed middle-aged men (n=4730) were recruited in 1970–71 from the Copenhagen Male Study, a large nationwide observational cohort study. CRF was measured at a single timepoint at baseline by measuring VO2 max during exercise on a bicycle ergometer. Study participants were then classified into to three groups based on their scores (low, normal or high – defined as ± 1 SD above or below the age-adjusted mean). Patients who reported pre-existing COPD were excluded. Follow-up took place over 46 years following the baseline assessment of CRF, with endpoints identified through national registers.
Risk of incident COPD was corelated with CRF at baseline, and was 21% lower in participants with normal CRF (hazard ratio [HR] 0.79, 95% confidence interval [CI] 0.63 to 0.99) and 31% lower in participants with high CRF (HR 0.69, 95% CI 0.52 to 0.91), compared to the low CRF group. The risk of death from COPD was also correlated with baseline CRF. Compared with the low CRF group, the estimated risk of death was 35% lower in participants with normal CRF (HR 0.65, 95% CI 0.46 to 0.91) and 62% lower in participants with high CRF (HR 0.38, 95% CI 0.23 to 0.61). Restricted mean survival times (RMST) analysis showed that, compared to the low CRF group, the normal and high CRF groups experienced a delay to incident COPD and death from COPD of 1.3–1.8 years. Crucially, testing for reverse causation had no significant effect on the results.
These study results suggest a long-term protective effect of good midlife CRF on risk of developing COPD and dying from COPD, which could have implications for how middle-aged men can reduce their risk of COPD.