Researchers at the University of Auckland found that birth order may affect the risk of cardiovascular disease and type 2 diabetes. (Agencies)
The study of middle-aged men living in New Zealand found that kids born first into their family were about 7kg heavier and had a bigger BMI than second-borns, a news channel reported.
They also had more insulin resistance, which can lead to health problems, researchers said.
There is some evidence to suggest birth order may influence the body's fat make-up and metabolism, from infancy to the teenage years. However, the potential impact in mid-life is unknown, researchers said.
Dr Wayne Cutfield and colleagues studied 50 overweight but otherwise healthy men between the ages of 40 and 50.
"First-born men were heavier and had lower insulin sensitivity than second-borns," researchers said. "Thus, first-born adults may be at a greater risk of metabolic and cardiovascular diseases," they added.
Researchers cautioned that larger studies are needed to fully evaluate this link.
The study was published in journal Scientific Reports.
Researchers at the University of Auckland found that birth order may affect the risk of cardiovascular disease and type 2 diabetes.