Submitted to: Journal of Clinical Endocrinology and Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/1999
Publication Date: N/A
Citation: Interpretive Summary: During the pubertal growth spurt, youngsters' bones accumulate calcium much more quickly. Recent studies have demonstrated a sharp decrease in the rate of calcium absorption and skeletal calcium accretion after girls reach menarche. We wanted to find out whether calcium metabolism changes during the transition from prepubertal development to early puberty, and if so, whether these changes in calcium metabolism are related to hormonal changes of puberty. We tracked a multiethnic group of girls from 8 to 11 years of age as they matured through three stages: early prepuberty, late prepuberty, and finally puberty. At each time point, we measured their blood levels of various hormones, used calcium isotopes to measure their calcium metabolism, encouraged the girls to maintain a 1200 mg/day calcium dietary intake, and did bone scans. We found a significant increase in the use of calcium associated with the onset of puberty, indicated by increased calcium absorption, accretion and deposition in bones. These findings show why it is so important to emphasize that girls receive sufficient calcium nutrition during early puberty. Our data also demonstrate that recently revised guidelines recommending an increase in calcium intake starting at age 9 are appropriate.
Technical Abstract: To evaluate the changes in calcium and bone mineral metabolism associated with early pubertal development, we performed longitudinal measurements of calcium absorption, calcium kinetics, bone mineral content, and hormonal markers related to puberty in a multiethnic group of girls beginning when they were 7- or 8-yr-old. Girls were Tanner stage 1 (breast) at the start of the study. They were placed on 1200 mg/day dietary calcium intakes and studied at approximately 6-mo intervals until they reached Tanner stage 2 (breast). Results at that time point (PUB) were compared to values approximately 1 yr earlier (LatePRE) and those 1 yr prior (Early PRE) to that. We found an increase in calcium absorption comparing PUB to LatePRE (n=34, 36.6+/-8.7% vs 30.7+/- 9.9%, p=0.002). Using whole-body dual-energy x-ray absorptiometry scanning, we found an increase in calcium accretion during the LatePRE to PUB period compared with the EarlyPRE to LatePRE time period (135+/-53 vs 110+/-45 mg/d, p=0.04). Calcium kinetic studies showed a significant increase in the bone calcium deposition rate (V o+), during the PUB compared to the Late PRE period. Hormonal and biochemical markers of bone development were also significantly increased at PUB compared to Late PRE. Hormonal activity, as evidenced by the unstimulated LH level, was significantly correlated to calcium accretion between the Late PRE and PUB studies and bone calcium deposition rate at the PUB study. These data demonstrate, using multiple independent methods, an increase in calcium utilization associated with the earliest physical signs of puberty.