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

UNLABELLED: 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.