Type 2 diabetes is a global public health concern, with increasing incidence and financial burden. Improving glycaemic control (measured by glycated haemoglobin, HbA1c) reduces risks of microvascular complications and cardiovascular disease events. Previous systematic reviews indicated aerobic exercise improves glycaemic control, but the optimum dose of exercise was unknown. This systematic review aimed to estimate the dose-dependent effects of supervised aerobic exercise training of 12 weeks or longer compared to no intervention or usual activity (control group) on levels of HbA1c in people with type 2 diabetes.
Guided by a prospectively registered protocol, sensitive searches of three databases (including PubMed, Scopus and Web of Science) and citation tracking were performed to identify randomised controlled trials evaluating supervised aerobic training. The participants were people with type 2 diabetes aged 18 years and older. The intervention was supervised aerobic exercise training of any intensity, modality, frequency and session duration in a program for 12 weeks or longer. Trials were excluded that implemented combined aerobic and resistance exercise training or had an active control group (e.g. resistance training). The primary outcome was change in HbA1c (%). In addition to reporting HbA1c, included trials needed to report the duration and intensity of the aerobic training for the intervention group. Two reviewers independently selected trials, extracted data and evaluated trial quality. Disagreements were resolved through discussion or arbitration by a third reviewer. Trial quality was assessed using the Cochrane risk of bias tool. Certainty of the evidence was evaluated using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. Dose-response meta-analysis was used to calculate the mean between-group difference and 95% confidence interval (CI) to illustrate the dose-dependent effect of duration (min/week) of supervised aerobic exercise on HbA1c. Pre-defined subgroup analyses were based on baseline weight and health status, exercise modality and intensity, intervention duration, presence of dietary co-intervention, and risk of bias assessment.
Twenty-six trials (1,253 participants) published between 1994 and 2020 were included in this review. The trials were conducted in North and South America, Europe, Africa, Asia and Oceania. Nineteen trials included men and women, five included women only and two included men only. Participants were a mix of weight ranges (normal weight, overweight and obese) and varied incidence of comorbidities or diabetic complications. Intervention duration ranged from 12 to 52 weeks. Frequency of supervised aerobic exercise training was 1-4 sessions/week. Twelve trials implemented a moderate intensity aerobic exercise training program, 10 trials a moderate-to-vigorous intensity program, and four trials a vigorous intensity program. All trials implemented continuous aerobic exercise, except for one study which implemented high-intensity interval training. Fourteen trials implemented a non-progressive aerobic exercise program and the other 12 trials progressed training in terms of frequency, intensity or duration.
Each 30 min/week supervised aerobic exercise reduced HbA1c by -0.22 percentage point (95% CI -0.29 to -0.15; 26 trials; 1253 participants; strong certainty). The subgroup analyses produced similar results for the baseline participant characteristics, program design and risk of bias. Levels of HbA1c decreased proportionally with an increase in the duration of supervised aerobic exercise training up to 140 min/week (MD: -0.88 percentage point, 95% CI -1.22 to -0.53), though the continued improvements after 100 min/week were trivial.
Every 30 min/week supervised moderate-to-vigorous intensity aerobic exercise training reduced HbA1c by 0.22 percentage point. The greatest reduction was seen at 140 min/week, however durations above 100 min/week do not further decrease HbA1c. The certainty of the evidence was rated strong based on the GRADE approach.
Jayedi A, Emadi A, Shab-Bidar S. Dose-dependent effect of supervised aerobic exercise on hba1c in patients with type 2 diabetes: a meta-analysis of randomized controlled trials. Sports Medicine 2022 Apr 1:Epub ahead of print.