Joint Effect of Central Obesity and Family History on Hypertension in Type 2 Diabetes: A Cross-Sectional Study in China

Purpose: This study aimed to examine the joint effect of central obesity (CO) and family history of hypertension (FHH) on hypertension in Chinese patients with type 2 diabetes mellitus (T2DM). Methods: A total of 1756 T2DM patients were enrolled from a cross-sectional study conducted in Zhejiang Province, China (March November 2018). Multivariate logistic regression models were used to analyze factors associated with hypertension and to assess COFHH interactions on both additive and multiplicative scales. Associations between waist circumference (WC) and systolic/diastolic blood pressure (SBP/DBP) were evaluated using generalized additive models (GAM) and Spearman correlation. The relationship between WC and hypertension was further explored using restricted cubic splines (RCS). Results: The prevalence of hypertension was 64.52%. WC was positively correlated with SBP (r = 0.25, P<0.001) and DBP (r=0.27, P<0.001), and showed a linear association with hypertension in both sexes (P for non-linearity>0.05). After adjusting for potential covariates, T2DM patients with both CO and FHH had a 4.64-fold higher risk of hypertension (95% CI: 3.22-6.67) compared to the reference group. A statistically significant additive interaction between CO and FHH was observed, with a relative excess risk due to interaction (RERI) of 1.59 (95% CI: 0.39-3.19), an attributable proportion (AP) of 0.34 (95% CI: 0.08-0.51), and a synergy index (SI) of 1.78 (95% CI: 1.13-2.79). No statistically significant multiplicative interaction was found. Conclusion: CO and FHH may jointly contribute to hypertension in Chinese T2DM patients through an additive effect beyond their individual associations. Maintaining a healthy WC is especially important for T2DM patients with a family history of hypertension.