| Background(1)Current situation and harm of obesity in children and adolescents.Overweight/obesity has become a global public health problem,as well as in China.The occurrence of obesity influences both short-and long-term health including growth and development,related chronic disease and mental health and other issues.(2)Physical activity,sedentary behavior and sleep are three kinds of activity behavior in 24 hours a day.In the traditional public cognition and previous related research,these three behaviors are identified as independently carried out and independently affect the risk of obesity.(3)The reasonable allocation of 24 h activity time is an important measure to curb the risk of obesity in children and adolescents.The correlation and changes between 24-hour activities may have additional effects on the risk of obesity in children and adolescents.To examine the relationship between 24-hour activity behaviors and body mass index(BMI)in a representative sample of Shanghai children using compositional analyses.Methods A cross sectional study was conducted on 321 primary school students(158 boys and 163 girls)aged 6-13 years old in Shanghai.Time spent in 24-hour activity behaviors was determined from accelerometry and children’s height and weight were measured by standard instruments.All analyses were conducted using the R statistical system:(1)Standard and compositional descriptive statistics were computed for comparison instead,the dispersion in compositional data sets is properly estimated using the variation matrix.(2)Compositional linear regression models were used to synthetically analyze the associations of distribution of time spent 24-hour activity behaviors with BMI and to investigate the effect of compositional isotemporal substitution of 24-hour activity behaviors with BMI.(3)The regression model first predicted the outcome value based on the mean time-use composition and subsequently predicted the outcome for a composition where 15 minutes of time had been reallocated from one behavior(eg,sleep)to an alternative behavior(eg,MVPA),keeping the 2 other behaviors constant(eg,sedentary and LPA).(4)This model was repeated for all possible reallocations between sleep,sedentary behavior,LPA,and MVPA for increments of 5 minutes.Predictions were plotted for reallocations of-60 to 60 minutes to aid interpretation where appropriate.Results(1)There are differences in the description of concentration trend between the two methods.The most obvious difference is found with the mean relative amount of time spent in MVPA and LPA.(2)A value close to zero implies that the times spent in the two behaviors involved in the ratio(arranged by rows and columns)are highly proportional.The variance of log(sleep/Sedentary behavior;)is 0.155,which reflects the highest(proportional)relationship or co-dependence(not correlation in the usual sense)between two behaviors.On the other end,it can be observed that the highest log-ratio variances all involve LPA,which shows that time spent in LPA is the least codependent on the other behaviors(ln MVPA/LPA=1.247;ln sedentary behavior/LPA=1.497;ln sleep/LPA=0.908).(3)The results of liner regression analysis with compositional data show that after controlling the sex and age,time spent in moderate-to-vigorous physical activity(MVPA)(β=-0.64,P <0.00)and light physical activity(LPA)(β=-0.44,P<0.05)was negatively associated with BMI in children,while the time spent in sedentary behavior(β=2.03,P<0.00)and sleep(β=1.78,P<0.00)was positively correlated with BMI in children.(4)The compositional isotemporal substitution models revealed reductions in BMI when a 15-min reallocation from LPA,sedentary behavior and sleep to MVPA,and from sedentary behavior to LPA.On the contrary,a 15-min reallocation from MVPA to LPA,sedentary behavior and sleep,and from LPA to sedentary behavior was associated with higher BMI.(5)According to the “dose-response” curves.First,the mutual substitution of MVPA and other activities has an asymmetric effect on BMI and the substitution of LPA and sedentary behavior has a symmetrical effect on BMI.Secondly,the best BMI reduction effect is to replace sedentary behavior with MVPA,thirdly,With the time of MVPA isotemporal substitute other behaviors increases the rate of decrease in BMI slows down,otherwise it increases rapidly.Conclusion(1)To examine the relationships between 24-hour activity behaviors and body mass index(BMI)in a representative sample of Shanghai children,It can provide more theoretical basis for the intervention and prevention of overweight or obesity in adolescents and children in China.(2)The school improves the activity intensity of students during recess and physical education,makes the conversion between LPA and MVPA,and reduces children’s BMI level.(3)Based on the best weight loss effect of replacing sedentary behavior with MVPA,schools can achieve the conversion between sedentary behavior and MVPA by reducing subject courses and increasing physical education during school,while after school,parents need to replace it with MVPA activities by appropriately shortening children’s sedentary behavior,such as learning,screen behavior,musical instrument practice and so on.However,under the premise of facing restrictions in practical operation,the author suggests that it can also be followed by reducing students’ sedentary time between classes,and trying to complete the conversion between sedentary behavior and LPA through walking,going up and down stairs,playing table tennis,etc.(4)While determining the optimal recommended amount,i.e.60 minutes of MVPA activity per day,it is also necessary to determine the minimum recommended amount-convert other behaviors of 5 minutes per day to MVPA and maintain 35 minutes of MVPA activity per day.Parents and teachers should take 24-hour activities as a whole and attach great importance to the positive effects of MVPA and LPA,try to reallocate time from ST to MVPA and LPA of children,so as to obtain better health benefits. |
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