Objective: To investigate the association between sedentary bouts and cardiovascular disease (CVD) risk factors, and to provide a reference for controlling and reducing the incidence of CVD in children. Methods: Cluster random sampling was used to select 356 students from five primary schools in Guangzhou. Sedentary behavior and physical activity were assessed using ActiGraph GT3X accelerometers, which were worn for 7 consecutive days. According to the sedentary bout duration of each participant, sedentary time was classified into categories of 1-<5, 5-<10, 10-<15, 15-<20 and ≥20 min bouts. Physical examinations were carried out to identify cardiometabolic risk factors. Multivariate linear regression was performed to analyze the relationship between sedentary bouts and CVD risk factors. Results: After adjusting for confounding factors, the time accumulated in sedentary bouts of 5-<10, 10-<15, 15-<20 min in duration were positively associated with higher cardiometabolic risk scores ( B =1.24， 2.01 ，2.40), negatively associated with lower HDL ( B =-0.13，-0.21，-0.27). The time accumulated in sedentary bouts of 1-<5, 5-<10 , 10-<15, 15-<20 min in duration were positively associated with BMI levels ( B =1.07，1.89，2.86，3.65), and waist circumference ( B =2.79，4.81，8.04，10.14)( P <0.05). Conclusion These results suggested that sedentary bouts of 5-<20 min were associated with an unfavorable cardiometabolic risk profile. Our finding suggests no more than 20 min accumulated sedentary time for children.

Objective: To investigate the associations between early life factors and the incidence of overweight and obesity and to provide a reference for childhood overweight and obesity prevention. Methods: A total of 5 172 children aged 6-11 years from 5 primary schools in Guangzhou were enrolled using stratified random cluster sampling method. After two years follow up, 3 315 children were included in the final analysis. Questionnaire was used to collect children s early life factors. Height and weight were measured objectively at baseline and follow up. Results: The incidence of overweight and obesity was 8.7% in children. After adjustment for confounders, results from the Logistic regression analysis showed that maternal pre pregnancy underweight was negatively associated with the incidence of childhood overweight and obesity( OR=0.54, 95%CI =0.38-0.76)( P <0.05). While excessive gestational weight gain during pregnancy( OR=1.55, 95%CI =1.14-2.10) and caesarean section ( OR=1.30, 95%CI =1.00-1.68) were positively associated with the incidence of childhood overweight and obesity( P <0.05). Conclusion Both excess gestational weight gain and caesarean section would increase the risk of the overweight and obesity of their offspring, while maternal pre pregnancy underweight would reduce the risk of childhood overweight and obesity.

Objective: To examine the association of sedentary behaviors with visual acuity among primary school children, and to provide a reference basis for the prevention and control of poor vision. Methods: Using stratified random cluster sampling method, a total of 4 969 students in grade 1-4 were selected from 5 primary schools in Guangzhou in 2017, and then were followed up in 2019. A validated questionnaire was used to collect data on children s sedentary behaviors, including doing homework, watching TV, playing computer/video games, and taking the bus/car between home and school. Visual acuity was measured in the baseline and the follow up using a 5 m standard logarithmic visual acuity chart. Multiple linear regression and Logistic regression were conducted to analyze the relationship between sedentary behaviors and visual changes. Results: The two year cumulative incidence of poor vision was 48.74%. Homework time was inversely associated with visual acuity of left eye( β=-0.012, 95%CI =-0.023- -0.002 ). Homework time was positively correlated with poor vision( OR =1.16, 95% CI =1.05-1.27). However, total sedentary time, screen time and bus/car time were not statistically associated with changes in visual acuity( P >0.05). Conclusion Increased homework time was associated with poorer vision in primary school students. Interventions to reduce the academic burden should be taken.