Firstborn Daughters More Likely To Be Overweight, Obese Than Younger Sisters

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Karen Lo|Aug. 28, 2015 8:00 am EST

A new study published in the Journal of Epidemiology & Community Health has found an unwelcome side effect to being the first in line — for the eldest daughter, the risk of being overweight is 29 percent greater than that of her younger sister or sisters, and the risk of obesity is a full 40 percent greater.

The paper's lead researcher, Dr. Wayne Cutfield, told U.S. News and World Report that the finding was the fourth such study to uncover certain health risks associated with being the firstborn, male or female.

Though the study is purely observational, Cutfield thinks that a possible reason for firstborns getting the short end of the stick may be due to a more restricted flow of the mother's blood to the placenta. Firstborns typically also weigh less than their siblings, which may be attributable to fewer nutrients reaching the fetus.

The study, which looked at over 13,000 pairs of sisters (approximately 27,000 women), corroborated with earlier studies that linked firstborn sons with greater height and weight.

"This study establishes an association in females, already seen in males, between the likelihood of obesity in adulthood and place in the birth order," Dr. David Katz, president of the American College of Lifestyle Medicine, confirmed to U.S. News.

"But by design, it cannot say for sure why such an association exists. Birth order is not a modifiable risk factor, but the obesogenic environment and a lifestyle at odds with weight control and health promotion certainly are. Our attention, as ever, should be directed there."