Quartiles Intercept Q4 Q3 Q2 Q1 hypertension dyslipidemia obesity time baseage GGT ALB GLO CHOL Hb MCV MCH WBC Estimate −3.9156 −0.3752 −0.5427 −0.3063 0 0.3269 0.1672 0.007 0.2352 0.0327 0.0056 0.0218 −0.0014 0.2507 −0.0101 −0.0935 0.2233 0.0753 Error 1.2888 0.1069 0.1084 0.1026 0 0.0875 0.0799 0.0774 0.0279 0.0033 0.001 0.016 0.0093 0.0405 0.0041 0.0186 0.0436 0.0236 Z −3.04 −3.51 −5.01 −2.98 ref 3.74 2.09 0.09 8.43 10.03 5.59 1.36 −0.15 6.19 −2.47 −5.04 5.12 3.1900 Pr > |Z| 0.0024 0.0004 <.0001 0.0028 ref 0.0002 0.0363 0.9277 <.0001 <.0001 <.0001 0.1735 0.8834 <.0001 0.0136 <.0001 <.0001 0.0014 RR 0.6872 0.5812 0.7362 ref 1.3867 1.1820 1.0070 1.2652 1.0332 1.0056 1.0220 0.9986 1.2849 0.9900 0.9107 1.2502 1.0782 0.5573 0.4700 0.6021 ref 1.1681 1.0108 0.8652 1.1978 1.0266 1.0036 0.9904 0.9805 1.1868 0.9820 0.8782 1.1476 1.0294 0.8473 0.7188 0.9002 ref 1.6461 1.3822 1.1721 1.3363 1.0399 1.0076 1.0545 1.0170 1.3911 0.9979 0.9445 1.3618 1.1293 Zhang et al. BMC Public Health 2012, 12:419 http://www.biomedcentral.com/1471-2458/12/419 Page 7 of 8 Table 7 The results of multiple GEE analysis for UA levels and hyperglycemia after adjusting other potential confounding factors lower 95 % Confidence Limits upper 95 % Confidence Limits baseline UA was reported as a durable marker of risk of hypertension [28]. In our longitudinal cohort study with 6 years of follow up, the GEE analyses confirmed that UA is an independent risk factor of hypertension in Chinese Han urban males; see Table 6. As found by Watanabe et al. [29], once elevated UA level causes sufficient renal injury, human body would develop salt-sensitive hypertension. Elevated UA also associates with increased amount of free radicals [30] and an oxidative stress, which may further abolish endothelium-dependent vasodilatation [31]. Finally, it has been well received that elevated UA level would increase the risk of dyslipidemia [12, 30]. Our longi- tudinal study also suggests a positive association between UA dyslipidemia; see Table 4. Although the role of UA in the metabolism of triglycerides and other lipids still remains unclear, it was believed that UA might be involved in either the overproduction or the reduction of clearance of lipids [32]. Conclusions Association between UA and cardiovascular diseases has been reported frequently recent years. Many research con- firmed that UA was a strong risk factor for cardiovascular diseases, especially MetS [33-35]. Our longitudinal study further verified that UA is an independent risk factor of MetS, higher level of UA leading to higher risk of MetS. All the analyses were based on GEE regression models with data from the longitudinal cohort study with Han Chinese urban male participants who were from middle to upper socioeconomic classes. Additionally, our study suggested that UA level be an independent risk factor to obesity, hypertension and dyslipidemia, but a protective factor to hyperglycemia. These findings are concordant with results from other studies on Asian populations, and jointly provide a basis to further develop a risk assessment model for predicting MetS using UA levels and other fac- tors in China. There were several limitations in the present study. Due to the fact that participants of the study who came to the hospitals mainly for physical examinations, they were man- datorily asked to report histories on medication for treating MetS or related medical disorders (e.g., hypertension). Thus we did not have data on medication in our GEE regression analyses in studying the UA–MetS association. Also consid- ering that our study contains only local males from rela- tively rich and educated families in Shandong province, and the fact that our analyses only covered a follow-up period of 6 years and no genetic information was included, it is expected a large scale longitudinal study is expected for a better and fully understanding of the target relationships. Additional file Additional file 1: Table S1. The distribution of UA levels and other potential confounding factors. Table S2 Numbers Participants at Each Year of the Study