Sibling absence and body mass index: From adolescence to adulthood

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.

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.

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.

Sibling absence is associated with higher BMI in adolescence and this difference persists into adulthood.