Gaining a younger sibling can reduce a child's obesity risk before reaching first grade, a study has found. Children who gained a younger sibling when they were between the ages of 2 and 4 had better BMI (body mass index) when they reached first grade.

By contrast, same-aged children who didn't gain a younger sibling during the same time period had almost three times increased obesity risk by first grade.

"Research suggests that having younger siblings – compared with having older or no siblings - is associated with a lower risk of being overweight," says Julie Lumeng, M.D., the study's senior author. Lumeng is a behavioral and developmental pediatrician at the C.S. Mott Children's Hospital in the University of Michigan.

Lumeng notes that, at present, they have little data on how the younger sibling's birth affected the childhood obesity risk. In their study published in Pediatrics, researchers analyzed the data of 697 children from across the nation. It is the first one to examine the link between becoming a big sister or brother to succeeding escalations in BMI.

There could be changes in the way the older child is fed when a younger sibling is born, the researchers hypothesized. It is believed that children cultivate life-long eating habits at the age of 3. The change in this time period could have significant influences in the dietary habits at a later age.

Another speculation is that the older child can develop lesser sedentary time now that a younger sibling is in the picture. The older child could become more engaged in "active play." These lifestyle habits can contribute to the development of a healthier BMI.

"When a new child is introduced, parents may relax their preoccupation with the older child's eating behaviors," says University of Minnesota researcher Jerica Berge, who was not involved in the research. This change allows the older children self-regulate whenever they ear and respond to their internal satiety signals.

Lumeng adds that further research is needed to analyze the association. There are growing concerns about the increasing rates of childhood obesity. If having younger siblings early in life can reduce a child's obesity risk and set the tone for dietary habits later in life, it could become a pattern that some families can recreate to help children lead healthier lives.