Diabetes Duration, Cholesterol Levels, and Risk of Cardiovascular Diseases in Individuals With Type 2 Diabetes

Objective: To investigate the association of diabetes duration with cardiovascular disease (CVD) risk and to examine the relationship between lipid levels and CVD risk over the duration. Methods: Using the Korean National Health Insurance Service Cohort database, we identified 2 359 243 subjects with type 2 diabetes aged >= 20 years in 2015 to 2016. Baseline lipid levels and diabetes duration were evaluated and followed up until December 2020 (mean follow-up, 3.9 years). Subjects were categorized according to diabetes duration (new-onset, < 5 years, 5-9 years, or >= 10 years). We analyzed the new-onset diabetes group with low-density lipoprotein cholesterol (LDL-C) < 70 mg/dL as the reference group. The hazard ratios (HRs) and 95% CIs of myocardial infarction (MI) and ischemic stroke (IS) were estimated using a Cox proportional hazards model adjusted for potential confounders. Results: During follow-up, 45 883 cases of MI and 53 538 cases of IS were identified. The risk of MI or IS began to increase at LDL-C >= 160 mg/dL in the new-onset diabetes group, and at LDL-C >= 130 mg/dL in the group with diabetes duration < 5 years. Among subjects with diabetes duration of 5 to 9 years, LDL-C levels of 100-129 mg/dL, 130-159 mg/dL, and >= 160 mg/dL were significantly associated with the risk of MI (HR [95% CI] 1.13 [1.04-1.22], 1.28 [1.17-1.39], and 1.58 [1.42-1.76], respectively). MI risk in the diabetes duration >= 10 years group was increased by 16%, even in the LDL-C 70-99 mg/dL population (HR [95% CI] 1.16 [1.08-1.25]). Conclusion: This population-based longitudinal study revealed that the LDL-C cutoff level for increasing the risk of CVD varied with diabetes duration and that the target LDL-C level should depend on the duration.