Fatter than your siblings? It could be because you're older

When you’re born influences many things in life (Image: Christina Kilgour/Getty)

Read more: Click here to read the original, longer version of this story.

EVER argued with your little sister? Now you can blame her for your weight problems too.

Birth order is linked to a variety of outcomes later in life – firstborn kids are often taller and have a higher IQ, for example. But they are also more allergy-prone and now, it seems, fatter. A study of more than 13,000 pairs of sisters in Sweden found that although eldest girls are born slightly lighter than their younger sisters, they are about 30 per cent more likely to be overweight by their mid-twenties (Journal of Epidemiology and Community Health, doi.org/65j). The findings back up earlier work in men.

Co-author Wayne Cutfield from the University of Auckland, New Zealand, thinks the effect could be down to a first-time mum’s inexperienced uterus. Blood vessels that nourish the fetus seem to be slightly thinner in first pregnancies, causing firstborns to be lighter and then overcompensate by eating more.

Gary Sacks of Deakin University in Melbourne, Australia, suspects social factors too. Maybe firstborns compete harder for food or get more money spent on them, he says.

This article appeared in print under the headline “She ain’t heavy, she’s my sister”