The Guangdong Nutrition and Health Survey (GNHS) 2002 was conducted by the Guangdong Province Center for Disease Control and Prevention (CDC) and the Health Bureau of Guangdong Province in 2002. The GNHS 2002 corresponded with the China National Nutrition and Health Survey (CNNHS) 2002 [9
], which covered 31 provinces, autonomous regions, and municipalities nationwide. Based on the CNNHS 2002 sampling protocols, eight urban areas or rural villages in Guangdong province were required to be sampled as a part of the CNNHS 2002. In order to have sufficient statistical power to analyze the provincial data independently and to obtain more reliable health information for the provincial population as a whole, five additional urban areas or rural villages were sampled in the GNHS 2002. Therefore, the GNHS 2002 has a representative provincial population sample from a total of 13 urban areas or rural villages (six urban city districts and seven rural villages) [8
]. Ethics approval was obtained from the Ethics Committee of China Centre for Disease Control. All participants gave informed consent prior to the survey.
The sampling methods and survey protocols as well as the quality control for the GNHS 2002 were similar to those for the CNNHS 2002 [9
]. The stratified multistage cluster sampling with probability proportional to size method was used. Briefly, the cities and counties of the province were classified into four strata (large cities; small to medium cities; class 1 and class 2 rural areas) based on their economic development levels identified by the central government of China. The first stage systemic sampling was conducted in each stratum: three districts from the large cities, three districts from the small to medium cities, four counties from the class 1 rural areas and three counties from the class 2 rural counties were randomly selected based on the population size. The second stage sampling was subsequently conducted in each selected districts or counties: three neighborhoods (urban) or townships (rural) were sampled from each selected districts or counties using the same systematic random sampling methods as that in the first stage. In the third stage, two residential committees (urban) or villages (rural) were sampled from each selected neighborhood or townships using the same systematic random sampling methods as those in the first and second stages. In the fourth stage, around 90 households with a record in the household registration system from each residential committees or villages were randomly sampled (the households in the registration system generally do not include migrant workers). All members of the selected household were invited to participate in the health survey, including a questionnaire interview and a general health examination. The overall response rate for the health survey was 89.45%. A total of 78 residential committees or villages and 7,180 households were finally included in the GNHS 2002 with 25,459 participants, representing the Guangdong provincial permanent residential population of 85,221,747 in 2000 [12
]. In addition to the general questionnaire interview and health examination, a third of the sampled households (2,424 households with 9,509 all age residents) were randomly selected for dietary intake examination, as well as blood sample laboratory test including fasting glucose and lipids profiles. Therefore, a total of 6,468 participants aged 20 years or above were included in the present analysis.
A central survey site was set up in each residential committee or village and the participants were required to be interviewed and receive the health examination on-site. All interviews and examinations following standardized protocols were conducted by physicians who received training specifically for the GNHS 2002. The questionnaire interview collected a wide range of information including demographic characteristics, life style and family and personal disease histories. Weight and height were measured with light indoor clothing and without shoes. Waist circumference measurement was made at minimal inspiration to the nearest 0.1 cm, midway between the lowest rib and the superior border of the iliac crest. Both weight and waist were measured in the morning before breakfast.
The blood pressure measurement was based on the 1999 World Health Organization/International Society of Hypertension guidelines on hypertension [13
]. Two consecutive readings of the blood pressure on right arms were taken after the participant in a seated position for 5 minutes rest. The average of the two readings was used for analysis.
Blood samples were drawn in the morning after an overnight fast using vacutainer tubes. Plasma glucose was measured within three hours after obtaining the blood sample using a spectrophotometer 721/722. For those participants with a plasma glucose level of 5.50 mmol/l or above, an Oral Glucose Tolerance Test (OGTT) was performed on the subsequent sixth day. Additional plasma samples were stored in airtight tubes at -80°C prior to shipment on dry ice to the CDC for the measurement of the lipids. Total cholesterol, triglyceride and HDL-cholesterol were determined using a Hitachi 7060 Automatic Chemical Analyzer in the CDC laboratory.
The International Diabetes Federation criteria (IDF) were used to define MetSyn in the present study because this definition considers the ethnic difference for central obesity. According to the IDF criteria, participants are classified as having MetSyn if they have central obesity (waist circumference > 90 cm for men and > 80 cm for women) plus any other two abnormalities of those shown below:
1. Hypertension: systolic blood pressure
130 mmHg, Or diastolic blood pressure
85 mmHg, or treatment of previously diagnosed hypertension;
1.7 mmol/l or specific medical treatment for this lipid abnormality;
3. Hypo-HDL-cholesterol: < 1.03 mmol/l for males or < 1.29 mmol/l for females;
4. Raised fasting glucose: overnight
The present study included all men and women aged 20 years or older. All data analyses were performed using SAS software, version 9.2 (SAS Institute, Cary, NC, USA). In a manner, similar to our previous survey analysis for the U.S. National Health and Nutrition Examination Survey (NHANES) [14
], the GNHS 2002 adopted a stratified multistage cluster sampling design. As such, the survey design parameters including weight, stratum and cluster were incorporated into all analyses. The weight was derived based on the provincial 2000 census data and associated administrative data. These weights account for the stratified multistage and the unequal selection probability survey design. The non-response information was also incorporated into the weight. PROC SURVEYMEANS and PROC SURVEYFREQ were used for the calculation of means and prevalence. All means and prevalence calculated in this study represented the overall estimates for the corresponding population aged 20 years or above in Guangdong province. PROC SURVEYREG and PROC SURVEYLOGISTIC were used to assess the differences between categories. Two sided p
values of less than 0.05 were considered statistically significant. 95% confidence intervals were calculated and presented in the present study. Domain statement was used for the subpopulation analyses.