We would like to thank Dr. Bardini and colleagues for their comment on the clinically important distinction between vitamin D formulations (Vitamin D therapy in adults with diabetes mellitus Nat. Rev. Endocrinol. 7, doi:10.1038/nrendo.2010.107-c1). In the Practice point box in the News and Views article (Shining a light: the role of vitamin D in diabetes mellitus Nat. Rev. Endocrinol. 6, 478–480; 2010),1 the dose of vitamin D supplementation refers to the inactive formulations of vitamin D, cholecalciferol (vitamin D3) or ergocalciferol (vitamin D2). These formulations, which require sequential hydroxylations in the liver and kidney to become active, are used for supplementation in the general population. The active formulation of vitamin D, 1,25-dihydroxyvitamin D2, is not recommended for usual vitamin D replacement except in special circumstances (for example, kidney failure, hypoparathyroidism).