Family structure in relation to body mass index and metabolic score in European children and adolescents.

Background: Living in single parent and blended families or as an only child-compared to living in two-parent biological families or with siblings, respectively-is associated with a higher body mass index (BMI) in cross-sectional studies. However, longitudinal research addressing the children's BMI in this context is scarce. Further, little is known about the association between family structure and metabolic health.

Objectives: This study aimed at investigating the association between both aspects of family structure with BMI and a metabolic score (MetS).

Methods: Cross-sectional data from 7804 children participating in the European multi-center I.Family study (2013/2014) and longitudinal data from 5621 children who also participated previously in the IDEFICS study (2007-2010) were used. Family structure was assessed by a detailed interview. BMI z-score and the MetS were based on measured anthropometry, blood pressure, high-density lipoprotein, blood glucose, and triglycerides. Linear regressions were performed to model associations between family structure with BMI and MetS.

Results: Children from single-parent families had higher BMI z-scores in the cross-sectional (β = 0.09, 95% confidence interval [CI]: 0.001 to 0.18) and longitudinal analyses compared to those from two-parent families. Cross-sectionally, the number of siblings was associated with lower BMI z-scores (β = -0.07, 95% CI: -0.10 to -0.03) and lower MetS (β = -0.14, 95% CI: -0.26 to -0.01). Longitudinally, only children between baseline and follow-up had higher BMI z-scores at follow-up (β = 0.07, 95% CI: 0.01 to 0.14) compared to stable siblings.

Conclusion: Obesity prevention measures should focus on single-parent households and families with an only child.