Lin et al. BMC Public Health 2010, 10:747 http://www.biomedcentral.com/1471-2458/10/747 130 mmHg or diastolic blood pressure (DBP) ≥ 85 mmHg. Hyperglycemia (Hyper-GL), hypertriglyceridemia (Hyper-TG) and low-HDL cholesterolemia (Low-HDL) were defined as fasting sugar ≥ 100 mg/dL, triglycerides ≥ 150.mg/dL and HDL < 40 mg/dL for males and < 50 for females (Bureau of Health Promotion in Department of Health, Taiwan) [11,12]. We specified the adults hav- ing MetS outcomes as those who did not fulfill MetS criteria in 2002 but did in 2007. Hyperinsulinemia(> 11.6 μU/ml) was arbitrarily defined as the top quartile level of our analyzed population as in other studies [13,14]. Elevated ALT (> 40 U/L), g-GT (> 50 U/L) and hyperuricemia (> 8 mg/dL) were defined as having a value greater than the normal range established by the Tao-Yuan General Hospital clinical laboratory [15]. Sonographic fatty liver was assessed using the follow- ing five parameters: liver-kidney contrast, gall bladder wall masking, blurring of wall of hepatic and portal veins, far attenuation of the diaphragm; and diagnosis was made according to previous reports [16]. Statistical analysis Baseline characteristics and abnormal rates were com- pared between subgroups with/without MetS outcome within five years using the t-test and the c2 test for cate- gorical and continual variables as appropriate. Three models of multivariate logistic regression were used to estimate the adjusted odds ratio (OR) and 95% confi- dence intervals (CI) of risk factors for predicting MetS development, under the adjustments for age, gender, previously documented predictors of MetS development (hyperinsulinemia, hyperuricemia, elevated liver enzymes, and sonographic fatty liver), lifestyle, each MetS compo- nent, the MetS component count and their combinations. A two-sided P-value < 0.05 was considered statistically significant. The synergistic index (SI) value of potential risk fac- tors A and B was therefore calculated by following the mathematical formula. A value of SI > 1.0 indicated that the interaction was more than an additive interaction, i.e., synergism [17]. SI = [OR (A plus B) − 1] [OR (A alone) + OR (alone) − 2] SAS version 8.0 (SAS Institute, Cary, NC, USA) was used for all statistical analyses. Results Within a five-year interval, 13% (175 out of 1384) of the participants met the criteria of MetS. Table 1 sum- marizes the overall baseline characteristics and abnorm- ality rates of the sample population in 2002. The initial mean age for this population was 32.3 years. Significant Page 3 of 8 differences were found when grouping baseline data according to the MetS outcome: as shown in the upper rows of Table 1, the adults having MetS outcome had significantly unfavorable initial measurements including baseline body mass index, waist, blood pressures, blood sugar, lipid profiles, liver enzymes, uric acid and insulin. Also shown in the lower rows of Table 1, this was a male-dominated (72.0%) working population; there were 58.6% participants initially having at least one MetS components; 26.1% smoked; 7.2% regularly consumed alcohol at least once a week and 32.1% did exercise at least three times per week. There were 27.4% of the par- ticipants having fatty liver. HBV and HCV carriers were 18.5% and 1.2% of sample population, respectively. With respect to MetS outcome, the adults initially having MetS components, the males, the habitual drinkers and the adults having fatty liver significantly prone to have MetS outcome within five years (Table 1). The initial prevalence rates of individual MetS compo- nents and their combinations are shown on Table 2. Upper rows demonstrate the prevalence of MetS com- ponents (not segregated from each other): COB, 3.9%; Hyper-GL, 20.5%; Low-HDL, 24.4%; HBP, 17.7%; and Hyper-TG, 13.7%. The initial abnormality rates of each component were significantly unfavorable for the adults having MetS outcome. Table 2 also shows that the base- line prevalence rate of single MetS component was 36.9%; and that 21.7% of sample population had two MetS components. Among the adults initially having only one MetS component, baseline distributions of each single MetS component were non-significantly dif- ferent between the groups with/without MetS outcome (Table 2, middle rows). In contrast, the adults initially having two MetS components predominated signifi- cantly in the group having MetS outcome (Table 2, lower rows). As shown in Table 3, 4 and 5 we constructed three models for the multivariate analyses. Utilizing a conven- tional model, after controlling for confounders, Table 3 demonstrates that MetS components, sonographic fatty liver, elevated g-GT and hyperinsulinemia were indepen- dent risk factors for MetS development among our early-middle-aged employees. Table 3 also indicates that the middle-aged adults getting central obesity had an OR of 7.5 (p < 0.01), which was far ahead of other indi- vidual risk factors (ORs ≤ 2.7). Taking MetS component count as a potential risk factor in model 2, Table 4 shows that adults having single and double MetS com- ponent had respectively a 2.8-fold (95% CI, 1.6-4.7) and 7.3-fold (95% CI, 4.3-12.6) increased risk of progression to MetS, compared with adults initially having zero MetS component count. In model 3 (Table 5), the entire single and two MetS component-carrying statuses, totally fifteen isolated assortments were introduced.