A 3-year longitudinal study of the association of physical activity and sedentary behaviours with childhood obesity in China: The childhood obesity study in China mega-cities

Objectives: Examine school children's physical activity (PA) and sedentary behaviours (SB) during 2015 to 2017 in China, and study their associations with children's weight status and relevant gender differences. Methods: This open cohort study included students from five major cities (Beijing, Shanghai, Xi'an, Nanjing, and Chengdu) across China. Data were collected from students in 2015, 2016, and 2017 (n = 5535) and from their parents and school personnel. Children's weight, height, and waist circumference were measured. SB and PA factors were evaluated using questionnaires. Mixed-effects models examined the relationship between weight status and PA-/SB-associated factors using this longitudinal data. Results: These children had high rates of obesity (12.4%, 95% CI 11.6%-13.3%) and central obesity (28.1%, 95% CI 26.9%-29.3%) during 2015 to 2017. Boys were more likely to have obesity than girls (16.5% vs 8.4%, respectively) as well as centrally obesity (36.3% vs 19.8%, respectively) and spent more time in screen viewing than girls (hours/week ± SD: 2015, 1.8 ± 2.5 vs 1.5 ± 2.0; 2016, 2.0 ± 2.4 vs 1.8 ± 2.5; 2017, 1.7 ± 2.3 vs 1.4 ± 2.1 hours/week). Those who walked <5 minutes on their average daily walk to school were more likely to have obesity (OR: 1.96, 95% CI 1.03-3.73) than those who spent ≥15 minutes on walking to school. When stratified by gender, this higher risk was only observed in girls (OR: 3.01, 95% CI 1.09-8.35). Children who spent more time in screen viewing were more likely to have obesity (OR: 1.13, 95% CI 1.06-1.21) and have central obesity (OR: 1.05, 95% CI 1.02-1.09). The association for obesity was consistent in boys and girls (boys, OR: 1.15, 95% CI 1.05-1.25; girls, OR: 1.12, 95% CI 1.00-1.24). Conclusions: More screen time and less walking time were risk factors for developing obesity in urban Chinese children. The associations varied by gender.