Calcium absorption and metabolism in children with juvenile rheumatoid arthritis assessed using stable isotopes.

Abstract

To assess calcium intake, absorption, urinary excretion and the fraction of urinary calcium originating from bone and diet in patients with juvenile rheumatoid arthritis (JRA). A dual tracer stable isotope technique was used to study 6 girls and 3 boys with JRA. Fractional absorption in the 6 girls, ages 4-9, with JRA was significantly lower than that in 10 similar, healthy girls (22.6 +/- 4.7% vs 30.4 +/- 8.4%, p = 0.033). Urinary calcium excretion tended to be higher in the girls with JRA than in controls, (2.9 +/- 1.5 vs 1.6 +/- 1.7, p = 0.15). The urinary calcium in patients with JRA was derived principally from bone, and there was no increase in diet derived urinary calcium. One of the boys with new onset JRA was markedly hypercalciuric and in negative calcium balance (-222 mg/day). Our data show that hypercalciuria in patients with JRA results from bone resorption, not hyperabsorption of dietary calcium and suggest that increases in calcium intake may benefit children with JRA.