Study population
Liaoning Province is located in Northeast China. Our previous study, used a cluster multistage sampling method, was also conducted in Liaoning province from October 2004 to June 2006 [11]. From January 2012 to August 2013, a representative sample of participants aged ≥ 35 years was selected to characterize the prevalence, incidence and natural history of cardiovascular risk factors in rural areas of Liaoning Province. Participants who were pregnant or had malignant tumors or mental disorders were excluded from the study. All the eligible permanent residents aged ≥ 35 years, living in their villages at least 6 months, from each village were invited to attend the study (a total of 14,016 participants). Of those, 11,956 participants agreed and completed the study to give a response rate of 85.3 %. The study was approved by the Ethics Committee of China Medical University (Shenyang, China). All procedures were performed in accordance with ethical standards. Written consent was obtained from all participants after they had been informed of the objectives, benefits, medical items and confidentiality agreement regarding their personal information. For participants who were illiterate, we obtained written informed consent from their proxies. In this report, we used only the data from participants who completed the study, which provided a final sample size of 5919 [4048 without antihypertension treatment (2152 men, 1896 women) and 1871 with antihypertension treatment (740 men and 1131women)].
Data collection and measurements
Data were collected during a single visit to the clinic by cardiologists and trained nurses using a standard questionnaire in a face-to-face interview. Before the survey was performed, we invited all eligible investigators to attend an organized training session. The training included the purpose of this study, how to administer the questionnaire, the standard method of measurement, the importance of standardization and the study procedures. A strict test was administered after this training, and only those who scored perfectly on the test were accepted as investigators in this study. During data collection, our inspectors had further instructions and support.
Data regarding the demographic characteristics, lifestyle risk factors, dietary habits, family income and family history of chronic diseases were obtained during the interview using the standardized questionnaire. The study was guided by a central steering committee with a subcommittee for quality control. Educational level was assessed as completion of primary school or less, middle school or high school and higher. Self-reported sleep duration (including nocturnal and nap duration) was obtained from the questionnaire. The responses were categorized into four groups: ≤7, 7–8, 8–9 and >9 h/d. Family income was classified as ≤5000, 5000–20,000 and >20,000 CNY/year.
According to American Heart Association protocol, blood pressure (BP) was measured three times at 2-min intervals after at least 5 min of rest using a standardized automatic electronic sphygmomanometer (HEM-907; Omron), which had been validated according to the British Hypertension Society protocol [12]. The participants were advised to avoid caffeinated beverages and exercise for at least 30 min before the measurement. During the measurement, the participants were seated with their arms supported at the level of the heart. The mean of three BP measurements was calculated and used in all analyses.
Weight and height were measured to the nearest 0.1 kg and 0.1 cm, respectively, with the participants wearing light-weight clothing and without shoes. Waist circumference (WC) was measured at the umbilicus using a non-elastic tape (to the nearest 0.1 cm), with the participants standing at the end of normal expiration. Body mass index (BMI) was calculated as the weight in kilograms divided by the square root of the height in meters.
Fasting blood samples were collected in the morning after at least 12 h of fasting. Blood samples were obtained from an antecubital vein into Vacutainer tubes containing ethylenediaminetetraacetic acid (EDTA). Fasting plasma glucose (FPG), total cholesterol (TC), LDL-C, HDL-C, TG and other routine blood biochemical indexes were analyzed enzymatically using an autoanalyzer. All laboratory equipment was calibrated, and blinded duplicate samples were used for these analyses.
Definitions
Hypertension was considered present if any of the following conditions were met: systolic blood pressure ≥ 140 mmHg, diastolic blood pressure ≥ 90 mmHg, or reported use of a medication for hypertension and the classification of BP in response to JNC8. Stage 1 hypertension Clinic blood pressure is 140/90 mmHg or higher. Stage 2 hypertension Clinic blood pressure is 160/100 mmHg or higher. Stage 3 hypertension hypertension Clinic blood pressure is 180 mmHg or higher [13]. TC, LDL-C. HDL-C and TG levels were classified on the basis of the National Cholesterol Education Program Adult Treatment Panel III [14]. Borderline high and high TC was defined as having TC levels of 5.17–6.20 mmol/L(200–239 mg/dL) and ≥6.21 mmol/L (≥240 mg/dL), respectively. Low HDL-C was defined as having HDL-C levels <1.03 mmol/L (<40 mg/dL). Borderline high, high and very high LDL-C was defined as having LDL-C levels of 3.38–4.15 mmol/L(130–159 mg/dL), 4.16–4.93 mmol/L(160–189 mg/dL), and ≥ 4.94 mmol/L (≥190 mg/dL), respectively. Borderline high, high and very high TG was defined as having triglyceride levels of 1.69–2.25 mmol/L (150–199 mg/dL), 2.26–5.64 mmol/L (200–499 mg/dL), and ≥5.65 mmol/L (≥500 mg/dL), respectively. Mixed hyperlipidemia was defined as TC ≥ 200 mg/dL plus TG ≥200 mg/dL. Severe hyperlipidemia was defined as TC ≥ 300 mg/dL and/or TG ≥ 500 mg/dL. Normotriglyceridemic hypoalphalipoproteinemia was defined as HDL-C <40 mg/dL and TG <200 mg/dL. According to the American Diabetes Association (ADA) criteria of 1997, impaired fasting blood glucose (IFG) was defined as FPG ≥6.1 mmol/L(<109.8 mg/dL) and <7.0 mmol/L (<126 mg/dL). According to the WHO criteria, the subjects with BMI ≥ 25 kg/m2 and <30 kg/m2 were diagnosed as overweight, and those with ≥30 kg/m2 as obese.
Physical activity included occupational and leisure-time physical activity. A detailed description of the methods for assessing physical activity has been presented elsewhere [15]. Occupational and leisure-time physical activity were merged and regrouped into the following three categories: 1) low—subjects who reported light levels of both occupational and leisure-time physical activity, 2) moderate—subjects who reported moderate or high levels of either occupational or leisure-time physical activity and 3) high—subjects who reported a moderate or high level of both occupational and leisure-time physical activity.
Statistical analysis
Descriptive statistics were calculated for all the variables, including continuous variables (reported as mean values and standard deviations) and categorical variables (reported as numbers and percentages). Differences between different dyslipidemia groups were evaluated using Student’s t-test, ANOVA, non-parametric test or the χ2-test as appropriate. Multivariate logistic regression analyses were used to identify independent factors of dyslipidemia among hypertensive adults with odds ratios (ORs) and corresponding 95 % confidence intervals (CIs) calculated. All the statistical analyses were performed using SPSS version 17.0 software, and P values less than 0.05 were considered to be statistically significant [7].
