Purpose: The aim of the study was to evaluate the relationship between changes in hemoglobin A1c (HbA1c) 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 HbA1c. 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 HbA1c. Results: Forty-eight studies (2395 subjects) were analyzed. The pooled WMD in HbA1c decreased significantly (−0.5% [95% confidence intervals: −0.6 to −0.4]) but contained significant heterogeneity (Q = 103.8, P < 0.01; I2 = 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 HbA1c. However, the overall duration of exercise (weeks) was significantly associated with the WMD in HbA1c (meta-regression coefficient: 0.01 [95% confidence intervals: 0.002−0.016]; R2 = 70.0%), and that result did not contain significant heterogeneity (P > 0.05; I2 = 14.7%). Conclusions: The exercise intervention decreases HbA1c in T2DM patients. In addition, exercise for an extended duration was associated with an increase in HbA1c, so the effects of exercise may be evident early on, but results suggested that exercise for a prolonged period alone may increase HbA1c.
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