Only children or siblings: Who has higher physical activity and healthier weight?

Background The influence of parents on physical activity (PA) and body weight of their children is confirmed by scientific studies and accepted by the professional community. However, it is not known whether only children or those with siblings have a higher level of PA and healthier body weight. Therefore, the aim of this study is to assess whether there are any differences in the daily step counts (SC) and the prevalence of obesity between only children and children with siblings, and whether the achievement of the daily SC recommendation by children/parents and parental obesity influence obesity in children with and without siblings. Methods The analysis included 566 families (10.6%/89.4% with single child/two or more children) with complete data of family members on weight status and ambulatory PA monitored with a Yamax pedometer during regular school/work week during spring and autumn between 2013–2019. The cut-point values of the daily SC recommendation amounted to ≥ 13,000/≥11,000 steps/day for 5–12 years old sons/daughters and ≥ 10,000 steps/day for 12–16-year-old adolescents and adults. The Chi-Square (χ2) test series was used to compare the achievement of the daily SC recommendation and the prevalence of normal body weight, overweight and obesity between only children and those with siblings. Logistic regression models (Enter method) were used to investigate whether the achievement of the daily SC recommendation by children/parents and parental obesity were associated with obesity in offspring in single-child families and families with more children. Results A significantly higher proportion of children with siblings (p < 0.01) achieved the recommended daily SC (51.8% vs. 31.7%) and showed a lower prevalence of overweight (16.2% vs. 20.0%) and obesity (7.1% vs. 20.0%) compared with only children. The achievement of the daily SC recommendation in children significantly (p < 0.05) decreased the odds ratio (OR) of obesity (OR = 0.22–0.34). Children with siblings had lower odds (OR = 0.41–0.54) of obesity than only children, but significantly (p < 0.05) only in mother-child dyads. Overweight/obesity of mothers significantly increased (p < 0.05) the odds of obesity (OR = 2.07) in their children. Conclusion Children from families with siblings have a higher amount of daily PA and healthier body weight than single-child families.