Lin et al. BMC Public Health 2010, 10:747 http://www.biomedcentral.com/1471-2458/10/747 many worksites in Taiwan, we have the opportunity to observe the development of MetS among middle-aged employees. Therefore, we conducted this workplace- based retrospective follow-up study to evaluate whether the readymade database from the MetS screening pro- gram is helpful in risk assessment for MetS development in middle-aged Taiwanese adults. Methods Study populations In accordance with the Labor Health Protection Regula- tion, 1648 employees from an electricity manufacturing company underwent compulsory health checkups in 2002 and 2007. The final analysis of this follow-up study included only the adults who did not fulfill the MetS criteria in 2002. Among the 1648 workers undergoing health examinations in both 2002 and 2007, 256 employees’ records were excluded from the present study because of having MetS in 2002. A total of 1384 adults (338 female and 996 male) constituted a cohort; and their records were used for endpoint analysis. This health examination was open to all registered employees during every working day, for one-month duration. The examinees were suggested to avoid strenuous physical exercise during the three-day span prior to undergoing the health examination. Subjects’ identities were anon- ymous and unlinked to the data. This analytical study followed the ethical criteria for human research; the study protocol (TYGH09702108) was reviewed and approved by the Ethics Committee of the Tao-Yuan General Hospital, Taiwan. Written informed consent was obtained from each participant. Demographics, lifestyle data, biological measurements and sonogram examinations In 2002, a questionnaire about baseline personal history, including physical exercise, smoking, drinking and diet- ary habits, was completed by the examinees. Physical examinations and blood tests were performed on all par- ticipants in both 2002 and 2007. The participants arrived at the health care unit of the factory in the morning between 07:30 and 09:30 AM, after an over- night 8 h fast. The physical examination records included measurements of waist circumference, weight, height, and blood pressure. Waist circumferences were measured midway between the lowest rib and the super- ior border of the iliac crest. After being seated for 5=min, sitting blood pressure was measured on the dominant arm using digital automatic sphygmoman- ometers (model HEM 907, Omron, Japan) two times at a 5 min interval; the mean of the reading was used for data analysis. After the physical examination, partici- pants were placed in a reclining position, and venous blood (20 ml) from an antecubital vein of the arm was Page 2 of 8 taken for subsequent tests. Blood specimens were centri- fuged immediately thereafter; and shipped frozen in dry ice to central clinical laboratory (certified by ISO 15189 and ISO 17025) in Tao-Yuan General Hospital. Glucose, triglyceride, high-density lipoprotein (HDL) cholesterol, alanine aminotransferase (ALT), g-glutamil transferase (g-GT) and uric acid analyses were conducted by a Hita- chi autoanalyzer, model 7150 (Hitachi, Tokyo, Japan). Hepatitis B virus (HBV) surface antigen (HBsAg) and anti-Hepatitis C virus (HCV) antibody were measured by the microparticle enzyme immunoassay using the Axsym System instrument (Abbott, Illinois, USA). Insu- lin was determined by radioimmunoassay using an Axsym autoanalyzer (Abbott, Illinois, USA). Since sonographic diagnosis for fatty liver has accepta- ble agreement among operators [8] and is widely accepted in many epidemiological surveys [9], this non- invasive method was used to diagnose fatty liver. In 2002, abdominal ultrasound examinations were per- formed for all examinees using convex-type real-time electronic scanners (Toshiba SSA-340 with 3.75 MHz convex-type transducer). Definitions We defined “having routine physical exercise” as answering, “Doing exercises more than three times every week.” To define “ever been a smoker”, the first ques- tion was “do you smoke? (1. Never, 2. Currently smoke, 3. Previously smoked, have since quit),” and this was fol- lowed by questions about frequency. We defined “ever been a smoker” as answering “yes” to question 2 or 3 and consuming at least 6 cigarettes daily for over one year. For defining “habitual drinker”, the first question was “do you usually consume alcohol? (1. No, 2. Yes),” and this was followed by questions regarding frequency and quantity; we defined “habitual drinker” in this study as saying “yes” to previous question and drinking at least one time weekly, over one year, with alcohol con- sumption more than 40 g/day for males or 20 g/day for females [10]. For defining “used to having snacks”, the first questions were “are you used to having snacks before sleeping?” and “are you used to having snacks between meals?” These were followed with questions regarding quantity. We defined snacking habits in the present study as more than three times per week. The standard portions of examples for snacks (fruit products, milk products, fried food, nuts, beans products, meat, and alternatives) were explained to examinees in questionnaires. MetS was diagnosed if the examinees had three or more of the following components: central obesity (COB) was identified as a waist circumference > 90 cm for male and > 80 cm for female; high blood pressure (HBP) was defined as systolic blood pressure (SBP) ≥