First-born Children Have Reduced Insulin Sensitivity and Higher Daytime Blood Pressure Compared to Later-Born Children

First-born Children Have Reduced Insulin Sensitivity and Higher Daytime Blood Pressure Compared to Later-Born Children

1. Ahila Ayyavoo*,
2. Tim Savage*,
3. José G. B. Derraik,
4. Paul L. Hofman and
5. Wayne S. Cutfield

- Author Affiliations

1. Liggins Institute (A.A.,T.S., J.G.B.D., P.L.H., W.S.C.), University of Auckland, Auckland, New Zealand; and Gravida: National Centre for Growth and Development (A.A., T.S., P.L.H., W.S.C.), Auckland, New Zealand

1. Address all correspondence and requests for reprints to: Wayne Cutfield, Liggins Institute, University of Auckland, Private Bag 92019, Auckland, New Zealand. E-mail: w.cutfield@auckland.ac.nz.

1. ↵* A.A. and T.S. contributed equally as first authors to the study.

Abstract

Background: Evidence suggests that first-born children and adults are phenotypically different to later-born children. Therefore, we aimed to assess whether birth order would be associated with changes in metabolism in childhood.

Methods: We studied 85 healthy prepubertal children aged 4 to 11 years, born 38 to 40 weeks’ gestation, and birth weight appropriate for gestational age: 32 first-born and 53 later-born children. Clinical assessments included measurement of children’s height, weight, fasting lipid and hormonal profiles, and dual-energy x-ray absorptiometry–derived body composition. Children also underwent 24-hour ambulatory blood pressure monitoring, and frequently sampled intravenous glucose tests with Bergman’s minimal model.

Results: First-born children were approximately 3 cm taller (height SD scores 0.88 vs 0.39; P = .009) and were slimmer (body mass index SD scores −0.05 vs 0.39; P = .048) than later-born children. Consistent with their taller stature, first-born children also had a 27% increase in IGF-I concentrations (227 vs 173 ng/mL; P = .002). Insulin sensitivity was reduced by 21% among first-borns compared to later-borns (8.4 vs 10.6 × 10⁻⁴/min/[mU/L]; P = .019). Further, 24-hour ambulatory blood pressure monitoring showed that first-borns had higher daytime systolic (+5 mm Hg; P = .032) and diastolic (+4 mm Hg; P = .029) blood pressure. Blood lipids were unaffected by birth order.

Conclusions: Although first-borns were taller and slimmer, these children had reduced insulin sensitivity and increased daytime blood pressure compared to later-borns. Thus, first-borns may be at a greater risk of metabolic and cardiovascular diseases in adult life. This finding may have important public health implications, in light of a worldwide trend toward smaller families.

• Received October 4, 2012.
• Accepted December 10, 2012.

• Copyright © 2013 by The Endocrine Society