WELLINGTON -- First-born children are more inclined to become overweight adults than their younger siblings, according to a New Zealand study published Monday.

Researchers at the University of Auckland studied 50 overweight, but otherwise healthy men between the ages of 35 and 55.

They found that first-borns were on average 6.9 kg heavier than second-borns and had a greater body mass index (BMI), while insulin sensitivity was also 33 percent lower in first-born men.

Both BMI and lower insulin sensitivity were considered risk factors for type 2 diabetes, hypertension and coronary heart disease, said a statement from the university.

The research, led by Professor Wayne Cutfield, added to understanding of the potential long-term health effects of birth order, following evidence suggesting that birth order could influence metabolism and body composition from infancy to early adulthood.