Cardiac autonomic neuropathy in type 2 diabetes mellitus (T2DM) patients is associated with high cardiovascular mortality. Heart rate variability (HRV) is the gold standard to measure cardiac autonomic neuropathy. We aimed to conduct a systematic review and meta-analysis to evaluate the impact of T2DM on HRV parameters.

Main databases were searched on 1st October 2017 using the keywords “diabetes” AND (“heart rate variability” OR “HRV”). Included articles reported HRV parameters in T2DM patients and healthy controls measured during 24hours. Measurements of HRV retrieved were: RR intervals, standard deviation of RR intervals (SDNN), percentage of adjacent NN intervals differing by more than 50 milliseconds (pNN50), square root of the mean squared difference of successive RR intervals (RMSSD), total power, low frequency (LF), high frequency (HF) and LF/HF ratio.

We included 1356 T2DM patients and 1576 healthy controls. T2DM patients had significantly (P<0.01) lower RR intervals (effect size=−0.61; 95 % CI [−1.21; −0.01]), lower SDNN (−0.65; [−0.83; −0.47]), lower RMSSD (−0.92; [−1.37; −0.47]), lower pNN50 (−0.46; [−0.84; −0.09]), lower total power (−1.52; [−2.13; −0.91]), lower LF (−1.08; [−1.46; −0.69]), and lower HF (−0.79; [−1.09; −0.50]). LF/HF did not differ. Levels of blood glucose, time from diagnosis of T2DM and HbA1c were associated with several HRV parameters.

T2DM was associated with an overall decrease in the HRV of T2DM patients. Both sympathetic and parasympathetic activity were decreased, which can be explained by the deleterious effects of altered glucose metabolism on HRV, leading to cardiac autonomic neuropathy.