Objectives: To examine if sibling absence is associated with higher BMI and to identify potential lifestyle factors underlying this effect; to determine if sibling effects on BMI persist into adulthood.
Methods: We used data from all five waves of the National Longitudinal Study of Adolescent to Adult Health to study the sibling factors and BMI of 3,563 participants who were in grades 7-12 at first wave (1994-95). These participants were measured again in the second wave (1996), the third wave (2001-2002), the fourth wave (2008-2009), and most recently, the fifth wave (2016-2018). We identified categories of siblings, comparing the BMI of those without siblings either to birth order or sibship size. BMI was calculated based on direct measurements of height and weight; underlying mechanisms were self-reported.
Results: Participants without siblings had significantly higher BMI than those with siblings, across waves, regardless of sibship size. Those without siblings had consistently higher BMI than middle-born, but not last-born participants. Adolescents without siblings reported eating fast food more frequently and spending more screen time.
Conclusions: Sibling absence is associated with higher BMI in adolescence and this difference persists into adulthood.
Keywords: BMI; adolescent; birth order; fast food; longitudinal; siblings; sibship size.
© 2022 World Obesity Federation.