Being a single child is a risk factor for overweight and obesity. Research has found that kids who don't have a sibling have a 50 percent higher chance of being overweight than kids who have a sibling and that the strength of the association between obesity and single child status increases if the child remains a single child in the house for long.

Researchers found that even after controlling other factors like parental weight, gender and birth weight, kids without any siblings still had a higher chance of being overweight or obese than their peers with siblings.

The study included more than 12,700 participants from 8 countries in Europe. According to the study's background information, more than 22 million children in Europe are overweight.

In the study, body mass index (BMI) of the participants was measured. Parents of participants were given questionnaire asking them about their child's lifestyle like eating habits, time spent watching television, playing, etc.

The study found that singletons or only children were more likely to play less and have a television in their rooms.

"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 siblings and obesity is strong. Indeed, being an only child appears to be a risk factor in and of itself," said Monica Hunsberger, researcher from Sahlgrenska Academy and one of the authors of the study.

Follow Up study

Overweight and obesity can be due to genetics or environmental factors. The study looked at how family structure influenced risk of obesity. Researchers say that they will now look for any causal links between obesity and family structures in follow up studies of the families who took part in the study.

"The fact that only children are more susceptible to obesity may be due to differences in individual family environment and family structure that we were not able to measure in sufficient detail. To better understand the causality, a follow-up study of these families will start next year," said Lauren Lissner, a researcher at the Sahlgrenska Academy and one of the study authors.

The study is published in the journal Nutrition and Diabetes.