Sure, firstborns may be smarter and all, but according to a new study, they're not doing so well in the health department. At least, not when it comes to firstborn males. (So you can tell your big brother to take that.)
A small study out of the University of Auckland in New Zealand, published in the journal Scientific Reports, looked at 50 overweight men ranging from age 40 to 50, and recorded both their BMIs and insulin-sensitivity stats. Then they cross-referenced where each man stood in the birth order, and turned up a few interesting stats...
For one, firstborns tend to be heftier than their younger counterparts. On average, they weighed 15 pounds more than those born later in the family line-up. And when it came to BMIs, firstborns averaged 29, versus 27.5 for second-borns. But that doesn't just translate into a bigger beer gut: that puts firstborns at a higher risk for some pretty serious health problems, like heart disease.
Older siblings are also more vulnerable to Type 2 diabetes, since their insulin sensitivity is 33 percent lower than the norm and their pancreas has to work overtime to compensate.
While you may want to take this all with a grain of salt (considering that the study only looked at overweight men living in urban areas), this isn't the first time birth order has been linked with weight. Other studies have also suggested that it may influence metabolism and body composition in kids. In those cases, researchers found that firstborns actually weigh less at birth than other kids—they just grow a whole lot faster during infancy.