Separate and combined effect of visit-to-visit glycaemic variability and mean fasting blood glucose level on all-cause mortality in patients with type 2 diabetes: A population-based cohort study

Aims To assess the independent and combined impacts of visit-to-visit fasting blood glucose variability (VVV-FBG) and mean fasting blood glucose level (M-FBG) on all-cause mortality. Materials and methods This prospective cohort study included 48 843 Chinese patients with type 2 diabetes. Cox proportional hazards regression models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) to evaluate the association of VVV-FBG and M-FBG with all-cause mortality. The potential nonlinear associations were examined using restricted cubic splines, and additive interaction was evaluated using relative excess risk due to interaction (RERI). Cox generalized additive models (CGAMs) and bivariate response surface models were further used to assess the combined effects of VVV-FBG and M-FBG. Results A total of 4087 deaths were observed during a median follow-up of 6.99 years. Compared with patients with values at the 5th percentile of average real variability (ARV) and M-FBG, we observed a 23% and 38% increased risk of premature deaths among those with values at the 95th percentile of ARV (HR 1.23, 95% CI 1.10, 1.37) and M-FBG (HR 1.38, 95% CI 1.26, 1.51), respectively. The interaction between glycaemic variability (ARV) and M-FBG was significant on both the additive scale (RERI 0.80 [0.29, 1.32]) and the multiplicative scale (HR 1.90 [1.10, 3.28]). High VVV-FBG and high M-FBG conferred the highest risk of all-cause mortality (HR 1.89, 95% CI 1.64, 2.17), compared to low VVV-FBG and low M-FBG. The CGAMs showed significant synergistic effects between glycaemic variability and M-FBG (P < 0.05). Moreover, a bivariate surface plot showed that risk of death increased more rapidly in type 2 diabetes patients with lower M-FBG combined with lower VVV-FBG. Conclusions The coexistence of high glycaemic variability and high glucose level might exacerbate the independent risk of premature mortality in type 2 diabetes patients, highlighting the importance of achieving normal and stable glucose levels simultaneously in the management of glucose.