Association between screen time, including that for smartphones, and overweight/obesity among children in Japan: NICE EVIDENCE Study 4

The association between screen time (ST), including that for smartphones, and overweight/obesity in children was examined separately for boys and girls, considering the influence of lifestyle factors. A cross-sectional study was conducted in 2,242 Japanese children (1,278 girls) aged 10-14 years. Overweight/obesity was defined by the International Obesity Task Force. Logistic regression analysis showed that only for girls, total ST (>= 4 h), smartphone ST (>= 3 h), and non-smartphone ST (>= 2 h) were all independently and significantly associated with overweight/obesity compared to <2 h total ST, non-use of smartphones, and <1 h non-smartphone ST. Thus, smartphone ST >= 3 h and non-smartphone ST >= 2 h were additively associated with overweight/obesity in girls only. Girls having smartphone ST >= 3 h and non-smartphone ST >= 2 h were 6.79 times (95% CI: 3.11-14.81) more likely to have overweight/obesity than girls with less usage of both. In girls, when total ST was >= 4 < 5 h or smartphone ST was >= 2 h, the significant association with overweight/obesity disappeared when physical activity was >= 60 min/day and sleep time was >= 8.5 h. In addition, none of these associations was significant in boys. In Japanese girls, smartphone ST, non-smartphone ST, and total ST were all significantly associated with overweight/obesity. To avoid overweight/obesity, it is suggested to keep smartphone ST, non-smartphone ST, and total ST to <3 h, <2 h, and <4 h, respectively, and to engage in sufficient physical activity and sleep time.