Differences in calcium metabolism between adolescent and adult females

A 3-wk metabolic study measured calcium balance in 14 white adolescent girls and 11 young adult women. Subjects were housed in a sorority to simulate a free-living environment. A 6-d menu cycle consisted of foods typically eaten by teenagers and averaged 1332 mg Ca/d. Adolescents had a significantly higher calcium balance of 326 +/- 107 mg/d (mean +/- SD) than adults, who averaged 73 +/- 104 mg/d (P < 0.001). No adult > age 21 y was in positive calcium balance. Adolescents had lower urinary calcium excretion values (P < 0.001), lower fecal calcium excretion (P < 0.01), and greater net absorption (P < 0.001) than adults. Calcium balance was negatively correlated with years postmenarche (r = -0.788, P = 0.0001) and height (r = -0.650, P = 0.001). Net calcium absorption was positively correlated with parathyroid hormone concentrations (r = 0.537, P = < 0.01). Thus, the growth demands of adolescents are met by more efficient net absorption and retention of calcium compared with young adults.