Researchers Uncover Link Between Birth Order And Being Overweight

redOrbit Staff & Wire Reports – Your Universe Online

First-born children could be more likely than their younger siblings to be overweight later on in life, researchers from the University of Auckland in New Zealand claim in research appearing in Thursday’s edition of the journal Scientific Reports.

The study found that children who were born first into a family were approximately 7 kilograms heavier and had a higher BMI than those born second, according to Helen Briggs of BBC News. Furthermore, they were found to be more resistant to insulin, which could lead to other health issues.

In the study, Dr. Wayne Cutfield, director of the university’s Liggins Institute and a professor of pediatric endocrinology, and his colleagues studied 50 overweight but otherwise healthy men between the ages of 39 to 51. They found that first-born men weighed more than second-born men, tended to be heavier for their height and were also roughly one-third less sensitive to insulin.

“The study… is the first of its kind in mid-life,” said New Zealand Herald reporter Martin Johnston. “It follows Liggins’ findings last year in children that those born first had higher blood pressure and 21 per cent lower insulin sensitivity than those with older siblings.”

Dr. Cutfield and his associates recruited 26 first-borns and 24 second-borns as part of their research, and used an oral glucose tolerance test in order to assess each subject’s insulin sensitivity. In addition, they report using other assessment methods, including DXA-derived body composition, lipid profiles and 24-hour ambulatory blood pressure in order to gauge the overall fitness levels of each study participant.

Despite the weight and insulin resistance differences, the investigators found no significant difference between first and second-born men in terms of ambulatory blood pressure, lipid profile or carotid intima-media thickness. Even so, the results suggest that first-born adults could face an increased risk of metabolic and cardiovascular diseases.

According to Christopher Allen, senior cardiac nurse at the British Heart Foundation, lower insulin sensitivity increases a person’s risk of developing type 2 diabetes. In addition, he said that it was important to “note where you carry your weight,” as those who carry extra fat in their middle are more likely to be insulin resistant.

“The significance of the latest study, although it is only a snapshot of one age group, is that it may reflect the metabolic effects of the shrinking of the typical New Zealand family since the 1960s,” Johnson added. “The fertility rate shrank from a peak of 4.3 births per woman in 1961, to 3.2 in 1971 – and was 2 in 2012. Smaller families mean a higher proportion of first-born people in a society.”