 Type 1 diabetes T1D is associated with increased urinary calcium loss, which may contribute to the low bone mineral density and increased fracture risk observed in patients with this condition. Chlorthalidone is a thiazide-like diuretic that is commonly used to reduce urinary calcium excretion in other conditions such as idiopathic hypercalciuria. Its safety and efficacy has not been specifically tested in an adolescent type 1 diabetes population. 