Objectives To study calcium homeostasis in 40 adolescent thalassaemic patients and the effect of an intramuscular injection of a megadose of vitamin D3 on serum 25-hydroxycholecalciferol (25-OH-D) concentration and other calcium homeostasis parameters in vitamin D-deficient (VDD) thalassaemic and non-thalassaemic adolescents.

Methods We measured some parameters of calcium homeostasis in 40 adolescents with thalassaemia and 40 non-thalassaemic adolescents. An intramuscular dose (10 000 IU/kg) of cholecalciferol was injected in those with VDD (40 thalassaemic and 26 non-thalassaemic adolescents) and their responses evaluated.

Results Out of 40 thalassaemic individuals, two had hypoparathyroidism and low 25-OH-D and two had hypocalcaemia with hypophosphatemia, high alkaline phosphatase (ALP), high parathyroid hormone (PTH) and low serum 25-OH-D (<20 ng/ml). The rest of the thalassaemic group (n  =  36) had low circulating 25-OH-D concentrations with normal serum calcium and PO₄ concentrations. Out of the 40 non-thalassaemic individuals, 26 had VDD (65%). Thalassaemic individuals with VDD had lower circulating PTH and ALP concentrations compared with non-thalassaemic individuals with VDD. An improvement of symptoms related to VDD had been reported in 18/26 of symptomatic thalassaemic and 12/16 of non-thalassaemic individuals at 1–3 months after therapy. After 3 months the serum 25-OH-D level was lower in the thalassaemic group versus the non-thalassaemic group but the majority of patients had 25-OH-D equal to or greater than 20 ng/ml.

Conclusion A high prevalence of VDD was detected in thalassaemic adolescents (100%). An intramuscular megadose of cholecalciferol is safe and effective for the treatment of hypovitaminosis D in thalassaemic and non-thalassaemic adolescents for 3 months but not for 6 months.