(HealthDay News) – Birth order may influence metabolic and cardiovascular disease risk factors, including insulin sensitivity and daytime blood pressure, according to a study published online Jan. 30 in the Journal of Clinical Endocrinology & Metabolism.

Ahila Ayyavoo, MBBS, from the University of Auckland in New Zealand, and colleagues examined whether birth order correlates with changes in metabolism in childhood in a study involving 85 healthy prepubertal children (ages 4–11 years, born at appropriate birth weight at 38–40 weeks of gestation). Of the participants, 32 were first-born and 53 were later-born children. The children underwent clinical assessments, 24-hour ambulatory blood pressure monitoring, and intravenous glucose tests with Bergman’s minimal model.

The researchers found that, compared with later-born children, first-born children were significantly taller, by approximately 3cm, and were significantly slimmer. First-born children also had a 27% increase in insulin-like growth factor-1 concentrations, consistent with their taller stature. First-borns had a 21% reduction in insulin sensitivity compared with later-borns and had significantly higher daytime systolic and diastolic blood pressure upon 24-hour ambulatory blood pressure monitoring. Birth order was not associated with blood lipids.

“First-borns may be at a greater risk of metabolic and cardiovascular diseases in adult life,” the authors write. “This finding may have important public health implications, in light of a worldwide trend toward smaller families.”

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