Effect of vitamin D supplementation on calcium absorption and retention in adolescent girls

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 D 3 /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) 2 D (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 Source Delavau, LLC