The relationship between the level of exercise and hemoglobin A1c in patients with type 2 diabetes mellitus: a systematic review and meta-analysis

Purpose The aim of the study was to evaluate the relationship between changes in hemoglobin A(1)c (HbA(1c)) and exercise levels in type 2 diabetes mellitus (T2DM) patients when performing various types of exercise. Methods The inclusion criteria were randomized controlled trials involving adults with T2DM, intervention involving exercise alone, the overall duration of intervention >= 12 weeks, and reporting HbA(1c). Weighted mean difference (WMD) was defined as the mean difference between the intervention group and the control group weighted by the inverse of the squared standard error for each study, and all WMDs were pooled as overall effects. A meta-regression analysis was performed to evaluate the relationship between the exercise level and the WMD in HbA(1c). Results Forty-eight studies (2395 subjects) were analyzed. The pooled WMD in HbA(1c) decreased significantly (-0.5% [95% confidence intervals: -0.6 to -0.4]) but contained significant heterogeneity (Q = 103.8, P < 0.01; I-2 = 36.6%). A meta-regression analysis showed that the intensity (metabolic equivalents [METs]), time (min/session), or frequency (sessions/week) of the exercise was not associated with the HbA(1c). However, the overall duration of exercise (weeks) was significantly associated with the WMD in HbA(1c) (meta-regression coefficient: 0.01 [95% confidence intervals: 0.002-0.016]; R-2 = 70.0%), and that result did not contain significant heterogeneity (P > 0.05; I-2 = 14.7%). Conclusions The exercise intervention decreases HbA(1c) in T2DM patients. In addition, exercise for an extended duration was associated with an increase in HbA(1c), so the effects of exercise may be evident early on, but results suggested that exercise for a prolonged period alone may increase HbA(1c).