Percent True Calcium Absorption, Mineral Metabolism, And Bone Mass In Children With Arthritis

Objective. To assess whether percent true calcium absorption (a) is normal and whether supplementation with placebo, vitamin D-3 (2,000 IU/day), calcium (1,000 mg/day), or vitamin D-3 plus calcium improves a, mineral metabolism, or bone mass accrual in children with arthritis.Methods. Eighteen children received all 4 treatments, each for 6 months, in 4 different, randomly assigned orders. Changes in levels of 25-hydroxyvitamin D (25[OH]D), 1,25-dihydroxyvitamin D (1,25[OH](2)D), parathyroid hormone, bone turnover markers, and minerals and in bone mineral content were measured. Calcium absorption was determined with a dual stable isotope method using Ca-48 administered intravenously and Ca-46 administered orally, and measuring Ca-48, Ca-46, and Ca-42 in a 24-hour urine specimen by high-resolution inductively coupled plasma mass spectroscopy. Wilcoxon's signed rank test was used both to identify significant change over the treatment period with a given regimen and to compare change with an experimental treatment versus change with placebo.Results. Percent true calcium absorption was in the lower-normal range and did not differ by treatment (mean :+/- SD 28.3 +/- 20.2% with placebo, 26.1 +/- 12.1% with calcium, 19.2 +/- 11.7% with vitamin D-3, and 27.1 +/- 16.5% with vitamin D-3 plus calcium). With vitamin D-3 and vitamin D-3 plus calcium treatment, 25(OH)D levels were increased and 1,25(OH)(2)D levels were maintained. Serum calcium levels were increased only with vitamin D-3 and vitamin D-3 plus calcium treatment. Levels of bone turnover markers and increases in bone mineral content did not differ by treatment.Conclusion. The findings of this study indicate that percent true calcium absorption is low-normal in children with arthritis. Vitamin D-3 at 2,000 IU/day increases serum 25(OH)D and calcium levels but does not improve bone mass accretion. Calcium at 1,000 mg/day also failed to improve bone mass.