Bone mineral metabolism in adolescents, as assessed by metabolic balance studies.

摘要

Maximization of peak bone mass during the adolescent growth spurt is recognized as protection against the development of osteoporosis later in life. The basis for setting calcium recommendations for adolescents is to identify the calcium intake at which maximal skeletal calcium retention occurs. The current calcium recommendation of 1300 mg/day was set based on data obtained in Caucasian girls. The purpose of this collection of work was to determine factors that influence calcium retention, including diet, gender, race, and hormone regulators, i.e. vitamin D, parathyroid hormone, and insulin-like growth factor (IGF-1).;Calcium balance studies were conducted in American white and black girls and boys, aged 11--15 years, matched for sexual maturity. A range of calcium intakes were tested in 3-week controlled feeding studies. Diet composites and all urine and feces were collected and analyzed for mineral content. For gender comparisons, 31 boys were studied on a range of calcium intakes. Hormonal regulators of growth, IGF-1 and IGF-BP3, were the most important biochemical determinants of calcium retention in boys. At any intake level, boys achieved higher calcium retention than girls on the same calcium intake. To compare calcium retention in black and white adolescent girls, subjects matched for weight and sexual maturity were tested on a range of calcium intakes. At any intake, calcium retention was significantly higher in black than white girls and sexual maturity influenced calcium retention. In 236 adolescent black and white boys and girls, serum 1,25D increased in response to a low calcium intake and apparent calcium absorption increased as 1,25D increased. Serum parathyroid hormone (PTH) levels and 1,25D were positively related. Serum 25D was inversely related to PTH, however, the relationship varied with race.;Magnesium retention in black and white girls acclimated to a low, medium or high calcium intake was compared when girls received a high or low sodium diet. Black girls retained more magnesium than whites, regardless of dietary sodium or calcium levels.;Higher calcium retention during adolescence may play a role in the development of higher bone mineral content in adulthood and in the prevention of the onset of osteoporosis.