Zhang et al. BMC Public Health 2012, 12:419 http://www.biomedcentral.com/1471-2458/12/419 adolescents [14], in an urban population in Turkey [15], and in many other populations. Particularly, the debate on whether UA should be viewed even as an additional com- ponent of MetS received intensive discussions [16]; and the relationship between UA and each MetS component was also controversial. In this paper, based on a large lon- gitudinal cohort study over 6 years, we confirmed that UA level is positively and significantly associated with risk of MetS among healthy male adults in Han Chinese of Shan- dong province, after adjusting other potential confounding factors using GEE regression analyses. This provides us a strong piece of evidence for developing risk assessment model for early screening of MetS. As an essential component of MetS, obesity was regarded as a main contributor of the increasing prevalence of MetS, because obesity was proved as a risk factor of hypertension, dyslipidemia and hyperuricemia [17]. The positive gradient of obesity with increasing UA level has been found among several recent studies [18, 19]. In this study, we found con- sistent results: in Chinese Han urban male population from middle to upper socioeconomic classes, UA levels of Q2, Q3, Q4 correspond to relative risks of 1.53, 2.04, and 2.51, respectively, in getting obesity (with Q1 as reference level; see Table 7. Additionally we found that the effect of UA on obesity become much larger, compared to MetS; see Table 3. In pathophysiology, it was explained in three ways for the fact that obesity causes higher level of UA in blood: (1) Page 6 of 8 obesity directly interferes with urate synthesis and excretion [20]; (2) obesity causes renal damage via glomerulus dys- function [21]; (3) obesity leads to dysfunction of the renin- angiotensin system, which would eventually results in frac- tional clearance of UA [22]. The association between hyperglycemia and UA, how- ever, still remained controversy. Most researches suggested that hyperglycemia and UA should be the pathophysio- logical underpinning of MetS a long time ago [23], and a number of prospective studies have provided evidence that individuals with higher UA are at a higher risk of diabetes [9, 24, 25]. Nonetheless, some studies claimed that UA is negatively associated with diabetes in Asian men [7, 12], and an inverse association between UA and fasting plasma glucose was also observed in adult residents of Taiwan [6]. In our study, also in Asian male population, Q2-Q4 of UA was found to have lower risk of hyperglycemia with adjusted OR from 0.58-0.74; see Table 5. This protective ef- fect can be explained in two ways: (1) UA-hyperglycemia association might be gender-dependent among Asian popu- lations (i.e., UA is a risk factor in females, but a protective factor in males); (2) the relationship might be nonlinear and hyperglycemia could impair tubular reabsorption of UA [6, 26]. UA was first demonstrated to be associated with hyper- tension by Mohamed in 1870 s [27], and in 2008, based on the large population in the Normative Aging Study. The Table 6 The results of multiple GEE analysis for UA levels and dyslipidemia after adjusting other potential confounding factors Intercept Q4 Q3 Q2 Q1 hyperglycemia hypertension obesity time baseage GGT ALB GLO CHOL Hb MCV MCH WBC Estimate −0.4838 0.4752 0.1815 0.0526 0 0.1725 −0.4309 0.2916 −0.23 −0.009 0.0106 0.0005 0.0101 −0.0465 0.0108 −0.097 0.2093 0.163 Error 0.8527 0.0713 0.067 0.0659 0 0.0795 0.0603 0.0485 0.0196 0.0023 0.0013 0.01 0.0063 0.027 0.0027 0.0114 0.0278 0.0166 Z −0.57 6.66 2.71 0.8 ref 2.17 −7.15 6.02 −11.75 −3.86 8.39 0.05 1.59 −1.72 3.96 −8.51 7.53 9.8 Pr > |Z| 0.5704 <.0001 0.0068 0.4247 ref 0.03 <.0001 <.0001 <.0001 0.0001 <.0001 0.9605 0.1109 0.085 <.0001 <.0001 <.0001 <.0001 RR 1.6083 1.1990 1.0540 ref 1.1883 0.6499 1.3386 0.7945 0.9910 1.0107 1.0005 1.0102 0.9546 1.0109 0.9076 1.2328 1.1770 lower 95 % Confidence Limits upper 95 % Confidence Limits 1.3985 1.0514 0.9264 ref 1.0168 0.5775 1.2173 0.7646 0.9865 1.0081 0.9810 0.9977 0.9054 1.0055 0.8875 1.1674 1.1393 1.8498 1.3672 1.1993 ref 1.3886 0.7315 1.4720 0.8256 0.9956 1.0131 1.0204 1.0229 1.0064 1.0163 0.9281 1.3017 1.2160