Exercise Intolerance in Type 2 Diabetes: A Systematic Review and Meta‐Analysis

Background To analyze the effect of type 2 diabetes (T2D) on cardiorespiratory fitness. Methods A multilevel model using restricted maximum likelihood method was used to analyze pooled data. Inclusion criteria included adults aged >18 years, one group of individuals needed to have been diagnosed with T2D, the control group must not have had insulin resistance, the study must report peak oxygen uptake, there was no exercise training before tests of functional capacity, and subjects may not have had overt cardiovascular disease, cancer, transplant surgery, or bariatric surgery. Moderators assessed were sample demographics (age, body mass index, sex, and time since T2D diagnosis) and cardiovascular outcomes (eg, echocardiographic variables, blood pressure). Results Absolute (cohorts n=30; subjects n=1152; mean difference, −0.29 L/min [95% CI, −0.37 to −0.22 L/min]; P <0.0001) and relative peak oxygen uptake (cohorts n=11; subjects n=1191; mean difference, −4.68 mL/kg per min; 95% CI, −6.94 to −2.42 mL/kg per min; P =0.001) were significantly reduced in the T2D group compared with control. Time since T2D diagnosis (β coefficient=−0.04, P =0.05) was a significant moderator of the absolute peak oxygen uptake pooled outcome. Early mitral inflow velocity/early mitral annulus velocity (β coefficient=−1.72, P =0.004) and left atrial volume index (β coefficient=−1.41, P =0.02) were significant moderators of the relative peak oxygen uptake model. Conclusions Markers of cardiac diastolic function (early mitral inflow velocity/early mitral annulus velocity and left atrial volume index) and time since diabetes diagnosis may contribute to exercise intolerance in T2D, although there is a lack of data in young/older adults and newly diagnosed individuals. As cardiorespiratory fitness predicts both all‐cause mortality and cardiovascular morbidity and mortality, these data have important implications for risk reduction in individuals with T2D.