Firstborns Have Higher Risk Of Diabetes, High Blood Pressure

Date: Feb-13-2013A new study from New Zealand finds firstborn children have reduced insulin effectiveness, a known risk factor for diabetes, and higher
blood pressure, compared to children who have older siblings. More research is needed to find out how these relate to risks in adulthood, since
puberty and lifestyle also have an influence, say the researchers.

Wayne Cutfield, of the University of Auckland, and colleagues, write about their study, thought to be the first to find a 21% drop in insulin
sensitivity among firstborn children, in the 30 January issue of the Journal of Clinical Endocrinology & Metabolism.

Cutfield tells the press in a statement released on Monday:

"Although birth order alone is not a predictor of metabolic or cardiovascular disease, being the first-born child in a family can contribute to a
person's overall risk."

In many countries, women are having fewer children, which means a greater proportion of the population comprises firstborn children. This study
suggests there could be important public health implications for countries like China, where the one-child policy has resulted in a significantly higher proportion
of firstborns.

A study published online in Science in January 2013 suggests that China's one-child policy, which was brought in to control the country's
ever-increasing population problem, may also have had some serious effects
on people's behavior and attitude.

Evidence from other studies suggests firstborn children and adults are biologically different from their younger siblings.

So Cutfield and colleagues set out to "assess whether birth order would be associated with changes in metabolism in childhood".

Their study, which was conducted through the University of Auckland's Liggins Institute, examined data on 85 healthy children aged from 4 to 11,
including 32 firstborns.

The data included measures of fasting lipid and hormone profiles, weight, height and body composition.

The children also had their blood pressure monitored with a 24-hour ambulatory device, and had frequent blood tests for glucose.

The results show that firstborns had a 21% lower insulin sensitivity and a 4 mmHg higher blood pressure.

"Blood lipids were unaffected by birth order," write the researchers.

They suggest the differences in insulin sensitivity and blood pressure could be due to changes that take place in the uterus during a first pregnancy,
changes that increase the flow of nutrients to subsequent fetuses.

However, they urge caution in using these figures as an indication of lifetime risk, as Cutfield explains:

"Our results indicate first-born children have these risk factors, but more research is needed to determine how that translates into adult cases
of diabetes, hypertension and other conditions."

He and his colleagues focused on children because puberty and adult lifestyle can influence insulin sensitivity.

There was, however, some good news for firstborn children: they tended to be taller (by an average of about 3 cm) and slimmer than later-born
siblings, even after adjusting for their parents' height and body mass index.

Written by Catharine Paddock PhD

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