Bac Giang city, located 60 kilometers far from Hanoi in the north. This is the provincial city and the socioeconomic and administrative hub of Bac Giang province. The city has over 102 thousand people; live in 7 inner communes and 9 suburban communes. Each commune has one primary school, one secondary school and all children of relevant age, who have permanent living status at this commune, are all enrolled in these schools.
The study population is secondary students enrolled in grade 6 to grade 9 with age ranging from 11 years old (grade 6) to 14 years old (grade 9) and a few with older age from total 16 secondary schools across the city.
From January to September of 2011.
This is a nested case control study in a cross sectional study. The first phase is a cross-sectional study when all study subjects were measured height and weight to identify the point prevalence of overweight and obesity. In the second phase, all subjects who were identified as overweight or obesity were paired with other none-cases subjects in the study to explore the associated factors of overweight and obesity.
Phase 1: Multi-stage cluster was applied to recruit study’s subjects. First, the list of 7 secondary schools in the inner communes and the list of other 9 schools in the suburban communes in Bac Giang city were collected from the City’s Department of education. Next, 2 schools in the inner communes and 2 schools in the suburban communes were randomly selected from these lists. Then, in each school, each grade is regarded as a cluster and 3 classes from each cluster were randomly selected into the study. All students in these classes were recruited into study and were measured their height and weight.
The calculation of sample size for this phase based on the prevalence of overweight, obesity of 8.3% from a recent study in an area in Vietnam that has similar socioeconomic status as compared to Bac Giang city [
Phase 2: All overweight, obesity students detected in the first phase will be recruited as cases and were paired with one control. The controls were students with the same age, gender and study at the same schools of cases and have normal BMI for age. Controls were selected from study subjects. Subjects in the phase 2 will be interviewed about their demographic information, eating habit, 24 h dietary, frequency of food consumption during the last week, physical activities and static activities. Parents or direct caregivers of these students were interviewed about their family’s socio-economic status.
Student’s height was measured by Microtoise height meter with the precision of 0, 1 centimeter. The meter was tested and placed in a stable location and adjusted to 0 value before each measument; students were asked to take out shoes and hat and were instructed to stand straightly in the meter. Height was recorded as meter with one decimal digit. Weight was measured by electronic SECA weighter with the precision of 0, 1 kilogram. The weighter was tested and placed in a stable location; students were asked to take out all of their shoes and coats and were instructed to straightly stand in the middle of weighter. Weight was recorded as kilogram with one decimal digit. Demographic, eating behaviors and other information of students were collected by a predesigned, piloted questionnaire via face-to-face interviews. Questions regarding eating habit, 24 h-dietary and frequency of food consumption in the last week were adapted from conventional questions which are used widely in other studies in Vietnam. Socio-economic status of students’ family was gathered via telephone-based interviews with their parents.
Anthrometric measurement and interviews were performed by experienced interviewers from Hanoi Medical University. Before fieldwork, all interviewers were well trained about the standard operation procedures to measure weight, height and administer interviews.
All children and their parents were carefully explained about the purpose of the study and orally accepted to participated to the study before data collection.
Obesity and overweight identification. Overweight and obesity was determined using body mass index per age per gender (BMI) (a measure of weight adjusted for height, calculated as weight in kilogram divided by the square of height in meter (kg/m2) and WHO Reference 2007 for 5 - 19 years to monitor the growth of school-age children and adolescents [
Nutrition need and diet’s balance assessment and analysis were calculated based on the Recommended Nutrition Need for Vietnamese, published by Vietnam National Institute of Nutrition [
The data then was cleaned before entering into EPIDATA software version 2.0. We used Stata software version 11 to analyze the data. Descriptive statistic was performed. c2 tests were done to test the differences of proportions of obesity and overweight among different age groups and gender. Logistic regression was performed to examine the relation between overweight, obesity and associated factors. All independent variables were first tested with univariate analysis. All important independent variables with P < 0.2 in the univariate analysis were put into multivariate logistic regression model. Multivariate logistic model was refitted, tested until the final model with the best fit was achieved.