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We investigated the relationship between IGF-I, gender, height, weight, body composition and birth size in 260 healthy 7- and 8-year-old children (139 females). All children were born term at Nepean Hospital, Western Sydney. Body composition was measured using dual energy X-ray absorptiometry. IGF-I levels were determined by radioimmunoassay. Girls had higher IGF-I levels than boys (20.2 ± 6.5 nmol/l compared to 15.9 ± 6.1 nmol/l, p < 0.001) but there was no correlation between age and IGF-I. IGF-I was positively correlated with height SDS (R² = 0.12), weight SDS (R² = 0.19), BMI SDS (R² = 0.18), total body fat (%) (R² = 0.14), and fat-free tissue/cm (R² = 0.03). After adjusting for gender and current weight, IGF-I-levels were inversely related to birth size – children with the lowest birth size and heaviest current weight had the highest IGF-I levels. This correlation between birth weight and IGF-I supports the hypothesis that the IGF-I axis is altered in babies who are small for gestational age.

Twin and family studies suggest that up to 75% of the variance in bone mineral density (BMD) is determined genetically and several candidate genes have been identified that might be involved in this process.1 Polymorphisms of the vitamin D receptor (VDR) gene causing diVerences in bone density between the homozygous haplotypes, were first described by Morrison et al in twin studies in an older female population.2 Subsequently, over 50 studies have been reported, examining the relation between BMD and VDR genotypes at the polymorphism (Apa I, Bsm I, and Taq I) sites at intron 8/exon 9 and the Fok I site at exon 2. 3 Variable eVects have been reported: from no diVerence in BMD being attributable to the VDR alleles to a diVerence of ∼ 10% between the homozygous alleles. A meta-analysis of 16 published papers by Cooper and Umbach confirmed a small eVect of VDR alleles of ∼ 2-3% at the hip and lumbar spine, and less at the wrist. 4 Cooper and other researchers suggested that the eVect of the VDR allele might be more apparent in younger populations.

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