Cardiorespiratory Fitness Is Impaired in Type 1 and Type 2 Diabetes: A Systematic Review, Meta-Analysis, and Meta-Regression

ABSTRACT Introduction Low cardiorespiratory fitness (CRF) increases the risk of cardiovascular disease by up to 8-fold, and is one of the strongest predictors of mortality. Some studies demonstrate impaired CRF in people living with type 1 and type 2 diabetes compared to those without diabetes, while others demonstrate no diabetes-associated impairment in CRF. Purpose We aimed to determine whether diabetes can influence CRF, and if so, identify clinical associations underlying diabetes-associated exercise impairments. Methods 68 studies were included in the quantitative analysis. Standardized mean difference (SMD) was calculated and meta-analyses and meta-regressions were performed by using a random-effects model. Results Diabetes is associated with a large negative effect on CRF (SMD = -0.80; p < 0.001)- an effect that is partially mitigated, but still significant, in those with high physical activity levels (SMD = -0.50; p = 0.007). A sedentary lifestyle (SMD = -0.83; p = 0.007), and the presence of clinical complications related to diabetes (SMD = -1.66; p < 0.001) predict a greater magnitude of CRF reduction in people with diabetes compared to controls without diabetes. Both type 1 and type 2 diabetes are independently associated with impaired CRF compared to controls without diabetes; however, the effect is significantly greater in those type 2 diabetes (SMD = -0.97; p < 0.001). Meta-regression analysis demonstrates the effects of diabetes on CRF are primarily associated with HbA1c levels for type 1 diabetes (B = -0.07; p < 0.001) and body mass index for type 2 diabetes (B = -0.17; p = 0.005). Conclusions These data demonstrate a negative influence of diabetes on the key risk factor of low CRF and provide critical insight into specific clinical markers of low CRF associated with diabetes.