In healthy adolescents, cross-sectional studies show either no or negative relationships between serum 25-hydroxyvitamin D [25(OH)D] and calcium (Ca) absorption. Using a 2-period metabolic balance study, the effect of vitamin D supplementation on Ca absorption and retention in adolescent girls was investigated. Eleven girls aged 12-14 y with a mean entry serum 25(OH)D of 35.1 nmol/L consumed a controlled intake (providing 5 μg vitamin D and 1117 mg Ca/d) for two 3-wk metabolic balance periods separated by a 1-wk washout period. Sunlight exposure was minimized by sunscreen with a sun protection factor ≥ 15. After the first metabolic balance period, participants received 25 μg/d cholecalciferol supplementation for 4 wk. Fractional Ca absorption was measured in each metabolic balance period using a stable Ca isotope method. All urine and fecal samples were collected and analyzed to measure net Ca absorption and Ca retention. Paired t tests and correlations were used to analyze the data. Daily supplementation with 25 μg vitamin D resulted in a mean increase in serum 25(OH)D of 13.3 nmol/L (P < 0.01) but a decrease in fractional Ca absorption of 8.3% (P < 0.05) and no significant change in fasting serum 1,25-dihydroxyvitamin D, parathyroid hormone, net Ca absorption, or Ca skeletal retention. In pubertal girls with vitamin D status considered insufficient in adults, vitamin D supplementation of 25 μg/d for 4 wk did not improve fractional Ca absorption, net Ca absorption, or Ca retention.

Dietary supplementation with CaCO(3) is effective in increasing calcium absorption and retention compared with placebo. But there is no advantage of small compared with large particle size CaCO(3) on calcium absorption and retention.

In adolescents, cross‐sectional studies show either no or negative relationship between vitamin D status and calcium absorption. Through a crossover‐design metabolic balance study, we investigated the effect of vitamin D supplementation on calcium absorption and retention in adolescent girls (mean serum 25(OH)D: 19.83 ng/ml). Sixteen girls age 11‐14 yrs consumed a controlled diet (providing 400 IU vitamin D and 1136 mg Ca/d) for two 3‐week metabolic balance periods separated by a 1‐week washout period. Sunlight exposure was minimized by sunscreen with a sun protection factor = 15. After the first metabolic balance period, subjects received 1000 IU vitamin D3/d supplementation for 4 weeks. Calcium absorption was measured each metabolic balance period using a stable calcium isotope method and indirectly through a 5‐hr PTH suppression profile. All urine and fecal samples were collected and analyzed to measure calcium retention. Statistical analysis was done by repeated measures ANOVA. Vitamin D supplementation resulted in a mean increase in serum 25(OH)D of 4.65 ng/ml (p=0.0007), but it had no effect on serum fasting 1,25(OH)2D (p=0.72), calcium absorption (p=0.33), PTH suppression (p=0.92), or calcium retention (p=0.10). Vitamin D supplementation at 1000 IU/d did not affect calcium homeostasis in pubertal girls with vitamin D status levels considered suboptimal in adults.Grant Funding SourceDelavau, LLC