Impact of cardiorespiratory fitness on survival in men with low socioeconomic status

Aims: Although both low socioeconomic status (SES) and poor cardiorespiratory fitness (CRF) are associated with increased chronic disease and heightened mortality, it remains unclear whether moderate-to-high levels of CRF are associated with survival benefits in low SES populations. This study evaluated the hypothesis that SES and CRF predict all-cause mortality and cardiovascular disease mortality and that moderate-to-high levels of CRF may attenuate the association between low SES and increased mortality. Methods: This study included 2368 men, who were followed in the Kuopio Ischaemic Heart Disease Study cohort. CRF was directly measured by peak oxygen uptake during progressive exercise testing. SES was characterized using self-reported questionnaires. Results: During a 25-year median follow-up, 1116 all-cause mortality and 512 cardiovascular disease mortality events occurred. After adjusting for potential confounders, men with low SES were at increased risks for all-cause mortality (hazard ratio 1.49, 95% confidence interval: 1.30-1.71) and cardiovascular disease mortality (hazard ratio1.38, 1.13-1.69). Higher levels of CRF were associated with lower risks of all-cause mortality (hazard ratio 0.54, 0.45-0.64) and cardiovascular disease mortality (hazard ratio 0.53, 0.40-0.69). In joint associations of SES and CRF with mortality, low SES-unfit had significantly higher risks of all-cause mortality (hazard ratio 2.15, 1.78-2.59) and cardiovascular disease mortality (hazard ratio 1.95, 1.48-2.57), but low SES-fit was not associated with a heightened risk of cardiovascular disease mortality (hazard ratio 1.09, 0.80-1.48) as compared with their high SES-fit counterparts. Conclusion: Both SES and CRF were independently associated with subsequent mortality; however, moderate-to-high levels of CRF were not associated with an excess risk of cardiovascular disease mortality in men with low SES.