The study, a collaboration between the University of Auckland’s Liggins Institute and a group of Swedish scientists, found firstborns were nearly 30 per cent more likely to be overweight than their secondborn sisters and 40 per cent more likely to be obese.
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They were also 29% more likely to be overweight and 40% more likely to be obese than their second born sisters.
The data showed that at birth, the firstborn sisters weighed a little less than their second-born sisters, on average.
The researchers wanted to find out if birth order affected adult women’s height and weight as it appears to among adult men. Weighed when they were between ten and 12 weeks pregnant, firstborn women were 1lb 4oz heavier on average than second-born sisters. A lot, according to a new study.
The researchers found that at birth, firstborns were actually much lighter than their second born.
A new study examines a phenomenon that perhaps we have subconsciously noted but never deeply examined: Firstborn women are more likely to be overweight or obese than their younger sisters.
Together, the four studies show an increased risk of obesity in firstborn men and women, Cutfield said.
“The steady decrease in family size over the last century has created a higher proportion of firstborns”, he said.
This study, published today (Aug. 26) in the Journal of Epidemiology and Community Health, is the largest of its kind carried out exclusively in adult female sibling pairs, the researchers said.
Just why isn’t yet known, but Prof Cutfield says it could have something to do with differences in antenatal blood supply from the mother to the placenta. “This reduces the nutrient supply, thus reprogramming the regulation of fat and glucose, so that in later life the individual is at risk of storing more fat and having insulin that works less effectively,”he writes”.
The researchers claim that the smaller the family size, the more likely the children are to be overweight – simply because more firstborns who are only children means more obese people.
“The differences of about 20 to 25 per cent in obesity and insulin sensitivity between firstborns and those born later are not large enough to be a major determining factor”.
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However, knowing your disease risk should always motivate you to make better decisions about your health, says Cutfield.
