Becoming a big brother or big sister before first grade may lower a child’s risk of becoming overweight or obese.
Research already suggested family structure may play a role in shaping weight, but a new study in the April 2016 issue of Pediatrics, “Effects of Sibling Birth on BMI Trajectory in the First Six Years of Life”, is the first to show how children’s body mass index (BMI) changes over time in relation to the birth of a younger sibling.
The study analyzed data from 697 children across the United States and found the birth of a younger sibling, particularly between 24 and 54 months of age, was linked to healthier BMIs from the time of the sibling’s birth until the older child reached first grade. Children who did not experience the birth of a sibling by first grade had nearly three times greater odds of obesity by first grade compared to children who experienced the birth of a sibling when they were roughly 2- to 4-years old.
The study’s authors said one possible explanation could be that parents may change the way they feed their child once a new sibling is born. Since children develop long-lasting eating habits at around 3 years old, changing dietary habits when a child is about that age could have a significant impact. Another explanation might be that children assume a caregiver or “teacher” role once a younger sibling is born, which often involves more active play and movement, contributing to healthier BMIs.