Prevalence of Triglyceride–Glucose Index-Defined Insulin Resistance and Its Association with Recorded Cardiovascular Disease Among Adults in the Municipality of Naples: A Cross-Sectional Primary-Care Study

Objectives: Assess the prevalence of insulin resistance (IR) in the adult population of the municipality of Naples in Italy and its association with cardiovascular diseases. Methods: We performed a cross-sectional analysis of adults aged 18–60 years without recorded diabetes who were followed by general practitioners affiliated with the COMEGEN cooperative, ASL Napoli 1 Centro. Participants were included if concurrent fasting glucose and triglyceride values from the preceding six months were available to calculate the triglyceride–glucose index (TyG), as a surrogate index of IR. IR was defined using an operational cut-off of TyG ≥ 8.5. Results: Of 17,510 selected records, 17,481 had calculable TyG; 5707 met the IR criterion (32.65%; 95% CI 31.96–33.35%). Recorded cardiovascular conditions were present in 44.98% with IR and 28.90% without IR. The adjusted odds ratio (OR) for IR was 1.252 (95% CI 1.137–1.379; n = 9866), and the adjusted prevalence ratio (PR) was 1.133 (95% CI 1.079–1.190). Adding IR to a model containing age, sex, and BMI increased the ROC AUC from 0.7438 to 0.7452 (p = 0.0477), a negligible absolute gain. Conclusions: TyG-defined IR was common and associated with recorded cardiovascular conditions, but offered little incremental discrimination; causality cannot be inferred from these cross-sectional data. However, the high prevalence of IR, associated with cardiometabolic risk, should prompt health institutions to inform the public about the existence of IR, a condition associated with an increased cardiometabolic risk that could be counteracted through healthier lifestyles, and encourage the scientific community to conduct prospective randomized controlled trials to determine whether early screening for IR, and subsequent intervention to counteract it, can yield benefits for cardiovascular outcomes.