Type 2 Diabetes is Associated with Lower Cardiorespiratory Fitness Independent of Pulmonary Function in Severe Obesity

Aims Both severe obesity and type 2 diabetes (T2DM) are associated with reduced pulmonary function and reduced cardiorespiratory fitness. We investigated whether T2DM further aggravates the impaired pulmonary function and cardiorespiratory fitness in subjects with severe obesity. Methods In this cross-sectional study pulmonary function (forced expiratory volume within 1 s, FEV ₁; vital capacity, VC) was assessed in 65 severely obese subjects with T2DM (T2DM group) and 65 severely obese subjects without T2DM (non-T2DM group), pairwise matched for sex, age, weight, and height. In 30 of the matched pairs, cardiorespiratory fitness was assessed by an incremental bicycle test (peak workload, W _peak, oxygen uptake, VO _2,peak). Results FEV ₁ and VC did not differ between the T2DM and non-T2DM group (all p≥0.110), whereas W _peak and VO _2,peak - absolute values as well as relative to body mass - were significantly lower in subjects with T2DM compared to those without T2DM (all p≤0.030). Objective markers of maximal exertion, i. e., maximal heart rate and respiratory exchange ratio, did not differ between the 2 groups (both p≥0.245). Conclusions The presence of T2DM in subjects with severe obesity is associated with lower cardiorespiratory fitness but with no further reduction in pulmonary function compared to subjects with severe obesity but without T2DM. While the cause-effect relationship of this association is not yet clear, these findings highlight the interplay between cardiorespiratory fitness and metabolic health, even in subjects with severe obesity.