Interactive effects of serum ferritin and high sensitivity C-reactive protein on diabetes in hypertensive patients.

Zhou, Juan; Wang, Ning; Wang, Dongxia; Zhao, Rui; Zhao, Dan; Ouyang, Binfa; Peng, Xiaolin; Hao, Liping

BACKGROUND Hypertensive patients, often characterized by chronic inflammation, are susceptible to diabetes. Evidence suggests that the positive association between serum ferritin (SF) and diabetes was affected by high-sensitivity C-reactive protein (hs-CRP), an inflammation marker. We investigate whether there was an interaction between SF and hs-CRP on diabetes in hypertensive patients. METHODS We analysed data of 1,735 hypertensive people in this cross-sectional study. Diabetes was diagnosed when fasting blood glucose ≥ 7.0 mmol/L and/or a previous clinical diagnosis of diabetes. Logistic regression models were used to estimate the association of the SF and hs-CRP with diabetes. Multiplicative interaction was evaluated by incorporating a cross-product term for SF and hs-CRP to the logistic regression model. Additive interaction was assessed by calculating the relative excess risk of interaction (RERI) and attributed proportion due to interaction (AP). RESULTS In the adjusted analysis, SF (highest vs lowest tertile: odds ratio [OR], 1.61; 95 % confidence interval [CI], 1.20-2.16) was positively associated with diabetes. There was no multiplicative interaction between SF and hs-CRP, but evidence of additive interaction in regard to diabetes (RERI: 0.86; 95 % CI: 0.06-1.67). Compared to the patients with low SF (lower two thirds) and low hs-CRP (≤ 2 mg/L), those with high SF (upper one third) and high hs-CRP (> 2 mg/L) had increased OR for diabetes (adjusted OR: 2.33 [1.65-3.30]), with 37.0 % of the effects attributed to the additive interaction (AP: 0.37; 95 % CI: 0.09-0.65). CONCLUSIONS Within a cross-sectional study consisting of hypertensive patients, co-exposure to high SF and high hs-CRP was synergistically associated with diabetes. Dietary intervention or pharmacological treatment to lowering SF concentration may help to reduce diabetes morbidity in hypertensive patient with chronic inflammation.