Primary aim: Compare change in estimated cardiorespiratory fitness (eCRF change) in rheumatoid arthritis (RA) patients with population-based age- and sex-matched controls during ~ 11-year follow-up and identify variables associated with eCRF change. Secondary aim: Compare eCRF level in RA patients and controls. eCRF change from the second (HUNT2 1995-1997) to the third (HUNT3 2006-2008) surveys of the Norwegian Trøndelag Health Study was compared between RA patients (n = 188) and controls (n = 26,202) attending both surveys. Predictors of eCRF change were identified by Lasso regression followed by multiple linear regression. Mean eCRF level in RA patients (n = 436) and controls (n = 67,910) was compared using age-adjusted linear regression stratified on sex, as well as two-sample t tests including RA patients (n = 432) and controls (n = 59,124) who attended either HUNT2, HUNT3 or both HUNT2 and HUNT3. The mean eCRF decline from HUNT2 to HUNT3 in RA patients was 8.3 mL min-1 kg-1 versus 6.7 mL min-1 kg-1 in controls (p < 0.001). The decline was faster in RA patients and larger with higher baseline age (standardized regression coefficient for RA patients: (- 0.482 × age + 0.044); controls: (- 0.367 × age, p < 0.001). The decline was also associated with smoking, cardiovascular disease, increasing body mass index, asthma, and hypertension. Mean differences in age-adjusted eCRF level for RA patients versus controls (p < 0.001): women HUNT2: - 3.2 mL min-1 kg-1; HUNT3: - 5.0 mL min-1 kg-1; men HUNT2: - 1.8 mL min-1 kg-1; HUNT3: - 4.0 mL min-1 kg-1. Higher age at baseline was associated with faster decline in eCRF. This change was more pronounced in RA patients than controls, indicating a larger negative effect on fitness of aging in RA. RA patients had lower eCRF compared to healthy individuals.
Keywords: Aging; Cardiorespiratory fitness; Population-based study; Rheumatoid arthritis.