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Your position in your family has been linked to a variety of outcomes later in life. It has been found that firstborn kids often grow taller, have a higher IQ and tend to be more conventional leaders. But not everything goes their way. They also tend to be more allergy-prone – and now, it seems – fatter too.
A study of more than 13,000 female sibling pairs in Sweden has found that although eldest girls are born slightly lighter than their second born sisters, they are about 30 percent more likely to be overweight – and 40 percent more likely to be obese – by their mid-twenties.
Because researchers can’t intervene and change someone’s birth order to see how that affects their weight, it’s difficult to confidently draw conclusions about the causes, says co-author Wayne Cutfield from the University of Auckland in New Zealand.
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But the findings back up earlier work that found similar effects among men, and a smaller study by Cutfield looking at risk factors in boys and girls that might predispose them to metabolic problems as adults.
He thinks the effect is likely to be biological, and could be down to the inexperienced uteri of the women’s mothers. The blood vessels that supply nutrients to the fetus seem to be slightly thinner in first pregnancies, and that seems to cause firstborns to be slightly lighter than second-born babies, on average. That could mean those babies then overcompensate for their experience in the uterus by eating more.
Read full, original post: Fatter than your siblings? It could be because you’re older
