ANN ARBOR, Mich. -- Becoming a big brother or big sister before first grade may lower a child's risk of becoming obese, a new study led by the University of Michigan suggests.
The birth of a sibling, especially when the child was between about 2 and 4 years old, was associated with a healthier body mass index (BMI) by first grade, according to the research. Children the same age who didn't have a sibling were nearly three times more likely to be obese by first grade.
The findings, which included 697 children across the U.S., appear in the April 2016 issue of Pediatrics .
"Research suggests that having younger siblings - compared with having older or no siblings - is associated with a lower risk of being overweight. However, we have very little information about how the birth of a sibling may shape obesity risk during childhood," says senior author Julie Lumeng, M.D., a developmental and behavioral pediatrician at U-M's C.S. Mott Children's Hospital.
"This study is believed to be the first to track subsequent increases in BMI after a child becomes a big brother or sister."
One possible explanation, the authors speculate, could be that parents may change the way they feed their child once a new sibling is born. With children developing long-lasting eating habits at around three years old, changing dietary habits may have a significant impact.
Authors also note that children may engage in more 'active play' or less sedentary time in front of screens once a younger sibling is born, contributing to healthier BMIs.
"We need to further study how having a sibling may impact even subtle changes such as mealtime behaviors and physical activity," says Lumeng, who is also with U-M's School of Public Health and Center for Human Growth and Development.
"Childhood obesity rates continue to be a great cause of concern. If the birth of a sibling changes behaviors within a family in ways that protect against obesity, these may be patterns other families can try to create in their own homes. Better understanding the potential connection between a sibling and weight may help health providers and families create new strategies for helping children grow up healthy."
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Additional Authors: Rana Mosil, Ph. D, of U-M and King Abdulaziz University in Jedda; Niko Kaciroti, Ph.D., of U-M; Robert Corwyn, Ph.D., of University of Arkansas at Little Rock; and Robert Bradley, Ph.D., of Arizona State University.
Funding: National Institutes of Health (Grant R01HD061356)
Disclosure: None
Reference: "Effect of Sibling Birth on BMI Trajectory in the First 6 Years of Life," Pediatrics , April, 2016. DOI: 10.1542/peds.2015-2456.
PEDIATRICS