Evaluation of bone mass and growth in young diabetics

To determine the relationships among bone mass, bone growth and serum glucose control in young, insulin-dependent diabetics, we performed photon absorptiometry and radiogrammetry on a clinically well-characterized group of 78 diabetics (mean age 15.2 yr, mean duration of diabetes 6.7 yr). Total and ionized calcium (TCa, ICa), magnesium (Mg), immunoreactive parathyroid hormone (iPTH) and phosphorus (P) were measured in fasting serum. Bone age was calculated from hand x-rays; and bone measurements, heights, and weights were standardized against normal groups of corresponding age, sex, and race. Mean deviation of bone mass measurement score was 1.24 SD below the normal mean (p less than .001); mean cortical area score was .22 SD and percent cortical area .25 SD below the normal means (both p less than .05). Radical width and metacarpal width for the diabetics were not less than normal. Mean percentiles for height and weight were 52.3 and 57.1 respectively, the latter significantly elevated (p less than .02). Bone mass and cortical area were inversely related to duration of disease (r = -.228, p less than .05; r = -.216, p less than .05). They were not correlated with serum parameters of mineral metabolism or of glucose control. Bone age was not significantly different from chronological age in those who had not achieved maturity (14.4 versus 14.5 yr). Mean age of menarche was 12.9 yr. When compared to normals the diabetic sample had diminished serum ICa (p less than .001), and Mg (p less than .001), though P and iPTH were not significantly different. We have demonstrated: (1) bone mass in this sample of juvenile diabetics is depressed, without evidence of impaired overall growth or delayed maturation, (2) this reduced bone mass probably results from a failure to gain the normal component of endosteal bone expected at this age, (3) this abnormality in bone growth progresses with disease but does not appear to vary with serum glucose control, and (4) in this population of diabetics there is a minimal but significant reduction in serum total and ionized calcium and serum magnesium without compensatory elevation of parathyroid hormone. The relationship of this metabolic abnormality of impaired bone growth in unknown.