Effect of Calcium Carbonate Particle Size on Calcium Absorption and Retention in Adolescent Girls

OBJECTIVE: Increasing calcium bioavailability by decreasing calcium salt particle size in the supplement may be one way to increase calcium absorption. The aim of the study was to compare (1) large versus small particle size CaCO3 supplements and (2) small particle size CaCO3 supplement versus placebo on calcium absorption and retention in adolescent girls. METHODS: Thirty-one adolescent girls, aged 11 to 14 years, participated in two 3-week calcium balance periods separated by a 1-week washout period. During both balance periods, the subjects consumed a controlled diet containing 804 mg/d calcium. Using a crossover design, one group (n = 19) received an additional ∼600 mg/d calcium of two ∼300-mg calcium doses as either large particle (18 µm; i.e., standard commercial form) or small particle (13.5 µm) CaCO3. A second group (n = 12) received ∼600 mg/d calcium from small-particle CaCO3 or placebo. RESULTS: The parathyroid hormone suppression curve, following a challenge, from the first arm of the study indicated that calcium absorption from the small particle size CaCO3 was less than that from the large particle size CaCO3. The parathyroid hormone suppression curve from the small particle versus placebo arm indicated that calcium absorption from small particle size CaCO3 was greater than placebo. Calcium balance (Ca intake – [urine Ca + fecal Ca]) demonstrated that the small particle size CaCO3 supplement increased Ca retention nearly 2-fold compared with placebo (p < 0.05; 496 ± 213 and 256 ± 94 mg/d, respectively). However, there was no significant difference in Ca retention due to small versus large particle size of CaCO3 (p > 0.05; 349.1 ± 131.6 and 322.0 ± 194.2 mg/d, respectively). CONCLUSIONS: Dietary supplementation with CaCO3 is effective in increasing calcium absorption and retention compared with placebo. But there is no advantage of small compared with large particle size CaCO3 on calcium absorption and retention.