The associations of serum C3 levels with the risk of diabetes. Data were fitted using Cox regression models of the restricted cubic spline with 3 knots at 25th, 50th, and 75th percentiles of serum C3. The reference point was the 10th of the C3 (1.08 g/L). The values outside the 1st and 99th percentiles were excluded in the plots. The solid line represents point estimation on the association of C3 with the risk of diabetes, and the dashed line represents 95% CI estimation. Covariates in the models were collected at baseline, included age, sex, BMI, serum C4 level, eGFR, smoking status, drinking status, family history of diabetes, hypertension, hyperlipidemia, education level, and physical activity.