Metabolic effects of interventions to increase exercise in adults with type 2 diabetes

Aims/hypothesis: The aim of this meta-analysis was to integrate the results of primary research testing the effect of diabetes self-management interventions that included recommendations to increase exercise on metabolic outcomes among adults with type 2 diabetes. Materials and methods: Extensive literature searching strategies were used to identify published and unpublished intervention studies that measured glycated haemoglobin outcomes. Primary study results were coded. Fixed- and random-effects meta-analytic procedures included moderator analyses. Results: Data were synthesised across 10,455 subjects from 103 research reports. The overall mean weighted effect size for two-group comparisons was 0.29 (higher mean for treatment than control). This effect size is consistent with a difference in HbA(1c) means of 0.45% (e.g. 7.38% for treatment subjects vs 7.83% for control subjects). For single-group studies, the overall mean weighted effect size was 0.32-0.34. Control group subjects experienced no improvement in metabolic control during participation in the studies. Interventions that targeted multiple health behaviours resulted in smaller effect size estimates (0.22) than interventions that focused only on exercise behaviours (0.45). Funded studies reported greater improvements in metabolic controls. Studies with a greater proportion of female subjects reported lower effect sizes. Baseline HbA(1c) and BMI were unrelated to metabolic outcomes. Conclusions/ interpretation: These findings suggest that self-management interventions that include exercise recommendations improve metabolic control, despite considerable heterogeneity in the magnitude of the intervention effect. Interventions that emphasise exercise may be especially effective in improving metabolic control. Primary research testing interventions in randomised trials to confirm causal relationships would be constructive.