Determinants of vitamin D levels in children and adolescents with Down syndrome.

Background. Poor studies have evaluated 25-hydroxycholecalciferol (25(OH)D) levels in Down syndrome (DS). Objective. To assess in DS subjects serum 25(OH)D value, to identify risk factors for vitamin D deficiency, and to evaluate whether a normal 25(OH)D value can be restored with a 400 I.U. daily supplement of cholecalciferol in respect to controls. Methods. We have longitudinally evaluated 31 DS patients (aged 4.5-18.9 years old) and 99 age- and sex-matched healthy controls. In these subjects, we analysed calcium, phosphate, parathyroid hormone (PTH), 25(OH)D concentrations, and calcium and 25(OH)D dietary intakes, and we quantified outdoor exposure. After 12.3 months (range 8.1-14.7 months) of 25(OH)D supplementation, we reevaluated these subjects. Results. DS subjects showed reduced 25(OH)D levels compared to controls (P < 0.0001), in particular DS subjects with obesity (P < 0.05) and autoimmune diseases history (P < 0.005). PTH levels were significantly higher in DS subjects than controls (P < 0.0001). After cholecalciferol supplementation, 25(OH)D levels were significantly ameliorated (P < 0.05), even if reduced compared to controls (P < 0.0001), in particular in DS subjects with obesity (P < 0.05) and autoimmune diseases (P < 0.001). Conclusions. Hypovitaminosis D is very frequent in DS subjects, in particular in presence of obesity and autoimmune diseases. In these subjects, there could be a need for higher cholecalciferol supplementation.