Like the rest of the developed world, Europe is getting a lot fatter, and public health experts in Europe have found a correlation for the upward spike in youth obesity - the low birth rate. They say only children, singletons, have a more than 50 percent higher risk of being overweight or obese than children with siblings. Over 22 million children in Europe are estimated to be overweight.

They examined data of over 12,000 children in eight European countries. The results were controlled for other influential factors, such as gender, birth weight and parental weight. The children's measured BMI was linked to a parental questionnaire that included questions relating to 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,” says Monica Hunsberger, a researcher at the Sahlgrenska Academy, University of Gothenburg, who contributed to 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,” says Lauren Lissner, a researcher at the Sahlgrenska Academy, University of Gothenburg.

The study also shows that obesity among children in general is three times more common in southern countries such as Italy, Spain and Cyprus than in Sweden and other northern countries, which disputes some of the claims about the 'Mediterranean Diet'.

Citation: M Hunsberger, A Formisano, LA Reisch, K Bammann, L Moreno, S De Henauw, D Molnar, M Tornaritis, T Veidebaum, A Siani and L Lissner, 'Overweight in singletons compared to children with siblings: the IDEFICS study', Nutrition and Diabetes (2012) 2, e35; doi:10.1038/nutd.2012.8