Kids without siblings are significantly more likely to be overweight or obese than kids who grow up with brothers and sisters, new research has found.

The study, by Swedish researchers at the University of Gothenberg, is based on an analysis of 12,700 children in eight European countries.

The results, published in the journal Nutrition and Diabetes, found kids aged 2 to 9 years were 50 percent more likely to be overweight if they did not have brothers and sisters compared to their pairs with siblings – largely due to lifestyle factors. The findings are based on a parental questionnaire about the children's eating habits, television viewing habits and amount of outdoor play time.

"Our study shows that only children play outside less often, live in households with lower levels of education more often, and are more likely to have televisions in their bedrooms. But even when we take these factors into account, the correlation between singleton status and overweight is strong. Being an only child appears to be a risk factor for overweight independent of the factors we thought might explain the difference," said researcher Monica Hunsberger.

Researchers said they now plan to take a closer look at factors that contribute to obesity in children with no siblings.