Cohort profile: Ho Chi Minh City Youth Cohort-changes in diet, physical activity, sedentary behaviour and relationship with overweight/obesity in adolescents

Objectives: The Ho Chi Minh Youth cohort study aimed to assess the change in nutritional status; indicators of adiposity; diet; physical activity and sedentary behaviours; home, neighbourhood and school microenvironments and their complex relationships in adolescents in urban areas of Ho Chi Minh City. Design: Prospective 5-year cohort. Setting: Systematic random sampling was used to select 18 schools in urban districts. Participants: Children were followed up over 5 years with an assessment in each year. Consent, from both adolescents and their parents, was required. At baseline, 759 students were recruited into the cohort, and of these students, 740 remained in the cohort for the first round, 712 for the second round, 630 for the third round and 585 for the last round of follow-up. Primary and secondary outcome measures: Anthropometric measurements were taken using established guidelines. Six main groups of exposure factors including dietary intake and behaviours, physical activity and sedentary behaviours, family social and physical environment, school environment, socioeconomic status and parental characteristics were measured. Results: Retention rate was high (77%). Within 5-year period, the prevalence of combined overweight and obesity using International Obesity Task Force cut-off values increased from 14.2% to 21.8%. Time spent on physical activity decreased significantly in the 5-year period from 87 to 50 min/day. Time spent on sedentary behaviours increased in the 5-year period from 512 to 600 min/day. Conclusions: The complete data analysis of this cohort study will allow a full exploration of the role of environmental and lifestyle behaviours on adolescent overweight and obesity and also identify the factors most strongly associated with excess weight gain and the appearance of overweight and obesity in different age groups of adolescents from this large city in Vietnam.