Scientists believe that the birth order of females may affect their weight over time, with first-borns having a higher body mass index and a larger chance of being overweight or obese than their younger siblings.
A new study, published in the latest edition of the
Journal of Epidemiology & Community Health, included data from 13,406 pairs of sister in Sweden — the largest study of its kind.
"The researchers wanted to find out if birth order affected adult women's height and weight as it appears to among adult men," a statement accompanying the research read. "They therefore drew on data from the Swedish Birth Register, which was started in 1973, and which contains information dating back to the first antenatal visit on virtually all (99 percent) births in Sweden."
The data found that first-borns often actually have a lighter birth weight than their second-born sisters but, as they each grow to become adults, the first-borns are 29 percent more likely to become overweight and 40 percent more likely to become obese than their second-born sisters. First-borns were also found to be slightly taller as well, according to the journal's statement.
"This is an observational study so no definitive conclusions can be drawn about cause and effect, and only young women were included in the study," the scientists said in a statement. "And [researchers] point to mounting evidence which suggests that first-borns may be more at risk of health problems, such as diabetes and high blood pressure, in later life than their siblings, although the potential underlying triggers for these differences are far from clear."
Dr. Maria Peña, director of New York City's Center for Weight Management at Lenox Hill Hospital,
told CBS News that the differences could be environmental.
"In many cultures, moms are more meticulous with their first-borns," she said. "With the very first-born, everyone's helping out and over-feeding the baby, making sure it's at a 'healthy weight.' But with second children, parents know what to expect and they're not so overprotective so maybe they feed them a little less."
The Swedish study's findings r
eportedly matched a similar study done on male birth order.
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