Increased efficiency of calcium absorption during short periods of inadequate calcium intake in girls

Abstract

Adequate calcium intake is essential for skeletal integrity, particularly during the period of peak bone mass acquisition from 9 to 17 y 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 aged 11.6 +/- 2.4 y after 10 d on both a low-calcium (7.05 +/- 2.03 mmol/d) and a high-calcium (35.30 +/- 2.28 mmol/d) diet. Fractional calcium absorption was determined by using oral (46Ca) and intravenous (42Ca) stable isotopes of calcium. During a low calcium intake, fractional calcium absorption was significantly greater (0.582 +/- 0.087 compared with 0.260 +/- 0.068, P < 0.0001) and urinary calcium excretion was significantly lower (1.30 +/- 0.83 compared with 3.08 +/- 1.98 mmol/d, P < 0.004) than values obtained during a high calcium intake. Concentrations of 1,25-dihydroxyvitamin D (combination of cholecalciferol and ergocalciferol) were greater during the low calcium intake, although the difference was not significant (108.7 +/- 30.6 compared with 90.0 +/- 25.1 pmol/L, P < 0.1; n = 9). Excretion of N-telopeptide was significantly greater during the low calcium intake (761 +/- 508 compared with 413 +/- 341 nmol bone collagen equivalent (BCM)/mmol 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 to conserve calcium required for bone mineral acquisition.

Changes in Calcium Kinetics in Adolescent Girls Induced by High Calcium Intake1

“…The lack of change in bone formation markers and the decrease in a marker of resorption support our results, showing that bone formation does not change and that resorption suppresses with high calcium intake. O'Brien et al (22) also reported that urinary telopeptides were lower in girls on a calcium intake of 35 mmol/day than FIG. 3.…”

Bone Turnover Response to Changes in Calcium Intake Is Altered in Girls and Adult Women in Families with Histories of Osteoporosis

“…Although there was no significant linear relationship between age and calcium absorption during the high-calcium period, the average fractional absorption values at each extreme of calcium intake were substantially higher in the girls in comparison with values observed in the adults, an effect that we and others have previously reported. (16,28) Serum levels of 1,25-dihydroxyvitamin D and PTH were not significantly increased in response to acute periods of low-calcium intakes. Dawson-Hughes et al also observed that despite initial elevations in 1,25-dihydroxyvitamin D levels, these levels returned to baseline following 14 days of a low-calcium diet.…”

“…Fractional calcium absorption data from the girls participating in this study have been previously reported. (16) …”

Scientific Opinion on Dietary Reference Values for calcium

“…Similar levels of fractional 47 Ca retention were reported in black and white women adapted to low-and high-calcium diets, despite higher concentrations of 1,25(OH) 2 D in black people, indicating that black people may be less responsive to the action of 1,25(OH) 2 D (Dawson-Hughes et al, 1993). However, one study found that postmenarchal African American girls had a higher absorption efficiency of calcium than Caucasian girls (Abrams et al, 1996). Absorption is also influenced by genotype, for example polymorphisms of the vitamin D receptor gene Fok1 (Abrams et al, 2005).…”

“…Thus, after rounding, an AI of 330 mg/day was set. Calcium requirements of children were estimated factorially, assuming a calcium retention of 140 mg/day for children aged 1 to < 4 years (Lynch et al, 2007), 120 mg/day for children aged 4 to < 7 years (Ames et al, 1999) and 150 mg/day for those aged 7 to < 10 years (Ellis et al, 1996;Abrams et al, 1999;IOM, 2011). Urinary calcium losses were assumed to amount to 37, 45 and 55 mg/day for these three age groups, respectively (Weaver, 1994), and endogenous faecal losses were estimated as 37, 40 and 50 mg/day, respectively (Abrams et al, 1991;Weaver, 1994).…”