Being a firstborn son may carry some social and cultural advantages, but that status also comes with some significant disadvantages when it comes to health, new research suggests. A small study of middle-age men in New Zealand has found that firstborns are more likely to be overweight and at risk for diabetes.
According to a Medical Xpress report on the study, researchers from the University of Auckland who tracked several groups of brothers found the oldest men in the family tended to weigh more (averaging more than 200 pounds) than their younger siblings (average weight: 185), even when the men were the same height.
The older brothers also had higher BMIs — 29.1 for the firstborns and 27.5 for the seconds. In addition, they tended to have higher amounts of body fat (older brothers averaged 32.2 percent body fat, compared with 29.9 percent for the younger).
There were also differences in insulin sensitivity, which was 33 percent lower in the firstborn men than the younger brothers. (When the body doesn't properly respond to insulin, it can lead to diabetes, heart disease and obesity.)
The researchers speculated that something may happen in the womb that makes firstborns more vulnerable to metabolic problems. First pregnancies cause changes in certain arteries in the uterus that may affect blood flow to the fetus, and those changes are permanent. That means firstborns don't get the benefit of these changes, but second children do.
The findings were published in the journal Scientific Reports.
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