Preserved cardiac vagal tone is associated with nocturnal glycaemic stability.

AIMS/HYPOTHESIS: Parasympathetic dysfunction is implicated in the pathogenesis of type 2 diabetes; however, its relationship with glucose regulation remains poorly understood. Thus, the aim of this study was to investigate the association between central parasympathetic function assessed as cardiac vagal tone (CVT) and continuous glucose monitoring (CGM) outcomes during sleep in individuals with and without type 2 diabetes. METHODS: This cross-sectional study included 20 individuals without diabetes and 40 individuals with type 2 diabetes, aged 45-75 years. They were home-monitored for 72 h, comprising nocturnal recordings of ECG-derived CVT measured using the ProCVT SmartSheet and Dexcom G6 CGM blinded to participants. Mean CVT was dichotomised into 'normal' CVT (≥5.0) and 'poor' CVT (<5.0). Only individuals for whom ≥70% of the total recording was classified as valid noise-free ECG data were analysed (N=50). RESULTS: Across all individuals, higher nocturnal CVT predicted a lower coefficient of variation in glucose (β=-0.8, p=0.030) and greater time in tight range (β=5.2, p=0.001). In individuals without diabetes, higher CVT was associated with reduced risk of hyperglycaemia (-10.2%, p=0.015), time above range (-11.8%, p=0.015) and time in moderate hyperglycaemia (-11.8%, p=0.015), and increased glucose mobility (β=0.014, p=0.029). In all individuals, poor CVT at the 15 min segment level was associated with a 1.9% increase in glucose in the subsequent period (p=0.049). CONCLUSIONS/INTERPRETATION: Preserved CVT, indicating normal central parasympathetic tone, is associated with a stable and dynamically regulated glucose profile with reduced adverse glucose mobilisation during sleep. This may have implications for glycaemic regulation in individuals with autonomic neuropathy.