First-Born Males Are at Higher Risk of Obesity: Study

A latest study shows that firstborn males are at greater risk of obesity.

Researchers at the University of Auckland in New Zealand compared the health of older and younger brothers. The participants were aged between 35 and 55 with a body mass index (BMI) ranging from 25 to 30, classifying them as overweight.

However, the researchers did not conduct the study on those with medical problems such as diabetes, high cholesterol, hypertension, or those who were taking any kind of medications that could affect those health conditions. They also exempted smokers and other tobacco users.

The researchers conducted the small study on 26 firstborns and 24 second-born male siblings.

The authors stated that the firstborns had an average height of five feet 10 inches and the younger brothers were slightly shorter with an average height of five feet nine inches. The study results showed much larger difference in weight between the two groups.

The study results found that the older brothers weighed around 200 pounds average whereas the younger brothers weighed an average of 185 pounds. This difference was seen in their  BMIs as well. The firstborns had an average BMI of 29.1 and the second-borns had an average BMI of 27.5. The researchers reported a slight but not significantly significant difference in body fat between the groups, reports MedicalXpress.

They also found one major difference between the two groups - insulin sensitivity. The firstborns had a 33 percent lower insulin sensitivity, which means their bodies had a tough time responding correctly to insulin. Poor insulin sensitivity can lead to diabetes, heart disease and obesity.

The researchers stated that placental blood flow might be the reason for such differences. It likely affects the firstborn's metabolism. During a woman's first pregnancy, arteries in the uterus undergo permanent changes. This alters the womb for all children born after the first child.

The findings were published in Scientific Reports.