Purpose: Cardiorespiratory fitness (CRF) is a strong predictor of future health, but measurements of CRF are time consuming and involve costly test procedures. We assessed whether a simple, non-exercise-based test of CRF predicted long-term all-cause and cardiovascular disease (CVD) mortality.
Methods: In this prospective cohort study, we used a previously published nonexercise test to estimate CRF in healthy men (n = 18,348) and women (n = 18,764) from the first HUNT study (1984-1986) in Norway. We used Cox regression to obtain HR for mortality during a mean follow-up of 24 yr. Assessment of model validity was performed by standard procedures of discrimination and calibration.
Results: CRF was inversely associated with all-cause and CVD mortality in men and women below 60 yr of age at baseline, after adjustment for confounders. For each MET-higher CRF (MET, approximately 3.5 mL·kg·min), HR for CVD mortality was 21% lower in both men (95% confidence interval (CI), 17%-26%) and women (95% CI, 12%-29%). HR for all-cause mortality was 15% (95% CI, 12%-17%) lower in men and 8% (95% CI, 3%-3%) lower in women for each MET-higher CRF. The ability of the model to discriminate mortality risk among participants below 60 yr was better for CRF (area under the curve (AUC), 0.70-0.77) compared with that for each variable that constituted the model (AUC, 0.55-0.63) and an aggregated sum of z-scores for each variable (AUC, 0.61-0.65). Comparison of observed and predicted risk indicated good model calibration.
Conclusions: This method of assessing CRF is feasible and practically useful in primary care for identification of apparently healthy individuals at increased risk of premature CVD disease and all-cause mortality.