Changes in the effects of living with no siblings or living with grandparents on overweight and obesity in children: Results from a national cohort study in Japan.

Effects of living without siblings and living with grandparents on overweight and obesity may change with child's age. We aimed to examine these effects from early childhood to school age at the national level in Japan. Subjects were 43,046 children born in Japan during two weeks in 2001 who were followed annually from 2.5 to 13 years of age in the Longitudinal Survey of Newborns in the 21st Century. We used measured body height and weight reported by participants at each survey and followed the criteria of the International Obesity Task Force to define overweight and obesity. Random-effects logit models by sex, adjusted for time-varying and time-invariant covariates, assessed odds ratios of overweight and obesity for living without siblings and for living with grandparents at each age. The likelihood of overweight and obesity was significantly higher at 8 years and older among children living without siblings, compared with those living with siblings, and odds ratios were highest at 11 years of age in boys (1.87, 95% confidence interval [CI]: 1.49, 2.33) and at 10 and 13 years of age in girls (1.75 [95% CI: 1.36, 2.23] and 1.73 [95% CI: 1.30, 2.31], respectively). It was also significantly higher at 5.5 years and older among children living with grandparents, compared with those living without grandparents, and odds ratios were highest at 10 and 13 years of age in boys (1.53 [95% CI: 1.30, 1.80] and 1.54 [95% CI: 1.27, 1.86], respectively) and at 11 years of age in girls (1.51, 95% CI: 1.24, 1.84). In Japan, living without siblings and living with grandparents may increase the likelihood of overweight and obesity at 8 and 5.5 years and older, respectively. Child's age should be considered during formulation of strategies for prevention of overweight and obesity in these groups.