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Hyperuricemia and metabolic syndrome (MetS) have been shown to increase the risk of hypertension, type 2 diabetes mellitus, and cardiovascular disease (CVD) and increase the risk of total and CVD mortality.1 2 Insulin resistance (IR) and central obesity have been recognised as the common underlying mechanism.3 4 The association between hyperuricemia and MetS has been studied, but most of these studies focused on Caucasians.5 In this study, we examined this relationship using five different definitions (proposed by the World Health Organization (WHO), the National Cholesterol Education Program Third Adult Treatment Panel (NCEP-ATPIII), the modified NCEP-ATPIII, the International Diabetes Federation (IDF), and the American Heart Association/National Heart, Lung, and Blood Institute (AHA/NHLBI)) in Taiwan.6
A total of 1305 subjects aged 40 years and over (633 men and 672 women; mean (SD) ages 57.7 (12.2) and 54.4 (10.0) years) were recruited in 2004 from a metropolitan city with a two-stage sampling design. Ethics committee approval was obtained from the Institutional Review Board of the China Medical University Hospital.
Subjects with hyperuricemia were older and heavier, and had higher body mass index (BMI), waist circumference (WC), fat percentage, blood pressure (BP), total cholesterol (TCHOL), low-density lipoprotein cholesterol (LDL-C), triglycerides, insulin, and homeostasis model assessment of insulin resistance (HOMA-IR) as well as lower high-density lipoprotein cholesterol (HDL-C) than subjects with normouricemia. After adjusting for age and BMI, hyperuricemia was significantly associated with all components of MetS except for central obesity, elevated fasting glucose and microalbuminuria.
The prevalence of hyperuricemia rose in proportion with increasing HOMA-IR, BMI, and age (fig 1). Using multivariate logistic regression with MetS as the outcome variable, we found that hyperuricemia and HOMA-IR were independent variables associated with MetS in each model after adjusting for age, gender, and BMI (table 1). By comparing hyperuricemic with normouricemic subjects, after adjusting for age, gender, BMI, and HOMA-IR, we found that the adjusted odds rations (ORs) of having MetS were 1.73 (1.24–2.34), 1.72 (1.20–2.47), 1.51 (1.02–2.24), 1.63 (1.17–2.27), and 1.70 (1.23–2.37) in models 1–5, respectively (table 1).
In this study, we found that the variables of obesity, IR, age, and hyperuricemia were independently associated with the prevalence of MetS using all definitions. Furthermore, even after adjusting for obesity and IR, we found that hyperuricemia was significantly associated with the prevalence and the individual components of MetS, using all definitions. Therefore, there was a positive correlation between hyperuricemia and MetS; however, this correlation could not be fully explained by obesity and IR. Several possible explanations have been proposed to explain the correlation. The endothelial dysfunction had been linked between MetS and hyperuricemia through oxidative-redox stress.7 Systemic inflammation and adipocytokines may also play a role between hyperuricemia and MetS. For example, studies have found that elevated C-reactive protein (CRP) or leptin levels are closely related to MetS and hyperuricemia.8 9 Inappropriate nutrition and physical inactivity could also contribute to this relationship. Studies found that diets rich in high fat, seafood and alcohol not only increase the levels of serum uric acid but also the incidence of MetS.10 Physical inactivity had been shown to increase the serum uric acid levels, stimulate the inflammatory process and increase the risk of MetS.
We demonstrated that the prevalence of MetS was independently associated with hyperuricemia after adjusting for age, gender, BMI, and HOMA-IR using five different definitions of MetS in Taiwan. Therefore, hyperuricemia should be treated as a major metabolic abnormality and should be included in the definition of MetS.
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Footnotes
Funding: This study is supported by grants from the National Science Council of Taiwan (NSC93-2314-B-039-025- and NSC94-2314-B-039-024-).
Competing interests: None declared.