Influences on skeletal mineralization in children and adolescents: evidence for varying effects of sexual maturation and physical activity.

Objective: To establish rates of skeletal mineralization in children and adolescents, and to identify factors that influence these rates.

Design: Three-year observational study.

Setting: University hospital.

Subjects: Ninety white children, aged 6 to 14 years.

Measurements: Bone mineral density of the radius, spine, and hip was measured at baseline and 3 years later. Physical activity was assessed by questionnaires at 6-month intervals and dietary calcium intake by diet diary 1 day per month for 36 months. Sexual maturation (Tanner stage) was determined by an endocrinologist at 6-month intervals, as necessary to classify children as prepubertal, peripubertal, or postpubertal.

Results: Skeletal mineralization accelerated markedly at puberty in the spine (0.077 vs 0.027 gm/cm2 per year, peripubertal vs prepubertal) and greater trochanter (0.050 vs 0.027 gm/cm2 per year), less markedly in the femoral neck (0.047 vs 0.030 gm/cm2 per year), and only slightly in the radius. Nearly one third (15 gm) of the total skeletal mineral in the lumbar spine of adult women (approximately 52 gm) was accumulated in the 3 years around the onset of puberty. Increases in height and weight were the strongest correlates of skeletal mineralization: weight changes were more strongly correlated with trabecular bone sites and changes in height with cortical bone sites. Increases in calf muscle area were strongly associated with mineralization, particularly in peripubertal children, and physical activity was associated with more rapid mineralization in prepubertal children.

Conclusions: Puberty has varying effects on skeletal mineralization depending on skeletal site; trabecular bone is apparently more sensitive to changing hormone concentrations. Physical activity and normal growth are also positively associated with skeletal mineralization, also depending on skeletal site and sexual maturation.