Calcium homeostasis in 40 adolescents with beta-thalassemia major: a case-control study of the effects of intramuscular injection of a megadose of cholecalciferol

Abstract

The prevalence of disturbed calcium homeostasis in adolescents with beta thalassemia major (T) varies among different populations. Moreover, the cholecalciferol uptake required to achieve or maintain any given serum 25-hydroxycholecalciferol level is not well known, particularly within ranges of the probable physiologic supply of the vitamin.

Objectives: The objectives of the study were to estimate the prevalence of abnormal calcium homeostasis in 40 adolescent thalassemic patients, and to investigate the effect of an IM injection of a mega dose of vitamin D3 on serum 25-hydroxycholecalciferol (25-OH D) concentration and other calcium homeostasis parameters in vitamin D deficient (VDD) thalassemic adolescents, and to compare these results with those for non-thalassemic adolescents with VDD.

Design: In this prospective study we measured parameters of calcium homeostasis in 40 adolescents with T and 40 matched non-thalassemic (NT) controls. An IM dose (10,000 IU/kg, max 600,000 IU) of cholecalciferol was injected in those with VDD (38 adolescents with thalassemia and 26 non-thalassemic adolescents). Parameters of calcium homeostasis were measured at intervals of 3 months during the course of the study.

Results: Of the 40 adolescents with T, 2 had hypoparathyroidism and low 25-OH D, and 2 had hypocalcemia with hypophosphatemia, high alkaline phosphatase (ALP), high PTH and serum 25-OH D below ng/ml. The rest of the patients (n=36) had low circulating 25-OH D concentrations with normal serum Ca and PO4 concentrations. Of the 40 non-thalassemic adolescents, 26 had 25-OH D levels below 20 ng/ml (65%). Patients with T and VDD had lower circulating PTH and ALP concentrations compared to non-thalassemic patients with VDD. Significant improvement of symptoms related to vitamin D deficiency was reported in 18 out of 26 of symptomatic T and 12 out of 16 of NT adolescents at 1 to 3 months after the injection. Three months after injecting vitamin D the mean serum 25-OH D concentration was lower in the T group as compared to the NT group but the majority of patients had 25-OH D levels equal to or greater than 20 ng/ml.

Conclusion: Vitamin D deficiency was detected in 100 % of our thalassemic adolescents. An IM injection of a mega dose of cholecalciferol is an effective therapy for treatment of hypovitaminosis D in thalassemic and non-thalassemic adolescents for 3 months but its effects do not persist for 6 months.