The bone mineral density (BMD) of the lumbar spine (L1-L4) was measured by dual energy x-ray absorptiometry (Hologic QDR 1000) in 135 healthy caucasian children, aged 1-15 yr, and values were correlated with age, height, weight, body surface, bone age, pubertal status, calcium intake, vitamin D supplementation, and serum bone gla protein. BMD increased with age in children of both sexes (r = 0.88; P less than 0.001) from 0.446 +/- 0.048 g/cm2 at 1 yr to 0.625 +/- 0.068 g/cm2 at 10 yr and 0.891 +/- 0.123 g/cm2 at 15 yr of age. The increase was steeper at the time of puberty, reaching values above 0.80 g/cm2 after puberty was achieved. There were no significant differences between boys and girls, except at the age of 12 yr when BMD was higher in girls than in boys (P = 0.007), probably because of the earlier onset of puberty in females. BMD was also highly correlated with height, weight, body surface, and bone age. BMD was not correlated with calcium intake when age was held constant, nor with vitamin D supplementation. Serum bone gla protein showed a steady increase during childhood, with peak values at 11-12 yr of age, and was weakly but significantly correlated with BMD (r = 0.27; P = 0.007). Because of low irradiation exposure, rapid scanning, and high precision, dual energy x-ray absorptiometry is a noninvasive method which is well adapted to the child. It should be helpful in the investigation and follow-up of children with diseases impairing bone metabolism.

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The body composition of 70 appropriate for gestational age newborn infants whose gestational age ranged from 32 to 41 weeks was determined by dual-energy X-ray absorptiometry during the first 48 h of life. The evolution of the bone mineral content, fat and lean mass was well correlated with gestational age (r = 0.66, r = 0.66 and r = 0.82, respectively) but even more closely with birthweight (r = 0.85, r = 0.91 and r = 0.97, respectively). The body composition of 20 symmetric small for gestational age infants (mean gestational age +/- SD = 38.1 +/- 1.2 weeks; mean birthweight +/- SD = 2117 +/- 183 g) was also studied. The total body fat, the lean mass and the bone mineral content of small for gestational age infants were decreased significantly in comparison with those of appropriate for gestational age infants with the same gestational age (p < or = 0.05, p < or = 0.0001 and p < or = 0.05) but was not significantly different from those observed in appropriate for gestational age infants of the same birthweight.

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