Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/1995
Publication Date: N/A
Citation: Interpretive Summary: Getting enough calcium is critical for young people, whose bones are growing rapidly and forming the foundation for the rest of their lives. However, the current dietary calcium intake of many girls is below the recommended daily allowance. We wanted to find out how well young girls' bodies can make use of low amounts of calcium in terms of absorbing it and excreting it in urine. We studied girls between 8-16 years old, using stable isotopes of calcium and found out that when they got minimal calcium, they absorbed it a lot better and excreted much less of it than when they got a lot of calcium. Therefore, during short periods (10 days) of very low calcium intake, young girls are able to significantly increase how well they absorb calcium and decrease their urinary calcium losses in order to save calcium for bone mineral buildup.
Technical Abstract: Adequate calcium intake is essential for skeletal integrity, particularly during the period of peak bone mass acquisition from 9-17 years of age. Currently, the calcium intake of many adolescent girls is below the recommended dietary allowance. The purpose of this study was to evaluate the ability of girls to respond to acute periods of inadequate dietary calcium intake. Calcium absorption was evaluated in 11 girls (11.6 +/- 2.4 y) after 10 d on both a low- (7.05 +/- 2.03 mmol/d) and a high- (35.30 +/- 2.28 mmol/d) calcium diet. Fractional calcium absorption was determined using oral (46Ca) and intravenous (42Ca) stable isotopes of calcium. During low-calcium intake, fractional calcium absorption was significantly greater (0.582 +/- 0.087 vs. 0.260 +/- 0.068, P<0.0001) and urinary calcium excretion was significantly lower (1.30 +/- 0.83 vs. 3.8 +/- 1.98 mmol/d, P<0.004) than values obtained during high-calcium intake. Concentration of 1,25-dihydroxyvitamin D were greater during low-calcium intake, although the difference was not statistically significant (108.7 +/- 30.6 vs. 90.0 +/- 25.1 pmol/L, P<0.1, n=9). Excretion of N-telopeptide was significantly greater during low-calcium intake (761 +/- 508 vs. 413 +/- 341 nM BCE/mM creatinine, P<0.02, n=9), indicating that bone resorption was increased. These results suggest that during short periods of inadequate calcium intake, girls are able to significantly increase the efficiency of calcium absorption and decrease urinary calcium losses in order to conserve calcium required for bone mineral acquisition.