Bone mineral density: correlation with body weight, height, bone age and insulin-like growth factor

Abstract

To evaluate bone mineral density and bone mineral content of skeleton and lumbar spine of pre-pubertal children and to correlate results thus found with sex, bone age, body weight, height and insulin-like growth factor 1 serum level. 26 boys and 12 girls aged between 7 and 8 years old, students from a São Paulo public school, were studied. They all presented weight and height between 2.5 and 97.5 percentiles of the Brazilian childreńs curve, lack of secondary sex characteristics, no reports on chronic diseases and normal physical examination. Bone age was determined from radiograms of the left hand and wrist. Serum levels of insulin-like growth factor 1 were measured by radioimmunoassay. Bone mineral density and bone mineral content were measured in skeleton and lumbar spine using a dual X-ray absorptiometry equipment. The mean values of skeleton bone mineral density found were 0.812 -/+ 0.057 g/cm(2) in the girls and 0.839 -/+0.053 g/cm(2) in the boys, while the respective mean lumbar values were 0.649 -/+ 0.092 g/cm(2) and 0.657 -/+ 0.062 g/cm(2). The mean values of skeleton bone mineral content found were 840 -/+ 181g in the girls and 919 -/+ 133 g in the boys, while the respective lumbar values were 13.3 -/+ 3,0g and 14.5 -/+ 2,4. It was found that the bone mass of children at this age corresponds to about 50% of the bone mass pick found in the young adult. No significant bone mass differences between sexes were found. No correlation was found between bone mass and insulin-like growth factor 1 serum levels. Positive correlations between bone mass and body weight and bone age were found. In pre-pubertal children (1) the analysis of bone mass should be interpreted mainly as a function of body weight and (2) bone mineral density of the lumbar spine and skeleton correlate with bone age and may represent an additional parameter of skeleton maturation.