Parents, take note! If you want to keep your children healthy and away from obesity, then give them a younger sibling.
The University of Michigan research, which included 697 children across the U.S., found that 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.
Children the same age who didn't have a sibling were nearly three times more likely to be obese by first grade.
Senior author Julie Lumeng said that the research suggests that having younger siblings, compared with having older or no siblings, is associated with a lower risk of being overweight. However, they have very little information about how the birth of a sibling may shape obesity risk during childhood.
Lumeng added that 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.
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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.
Lumeng concluded that 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.
The findings are published in Pediatrics.