To the editors,

We read with interest the position paper of the Spanish Society for Bone Research and Mineral Metabolism (SEIOMM) on COVID-19 and vitamin D, recently published in your journal¹. This document helps clarify the role of vitamin D in this infectious disease. One of its conclusions caught our attention. In the final section on the risk/benefit ratio of administering vitamin D, it stated that "it is considered that the administration of 10,000 IU/day of cholecalciferol or 4,000 IU/day of calcifediol is safe". This assertion is bibliographically referenced with a review on the benefit-risk balance of vitamin D by Bischoff-Ferrari et al.² In this paper, an evaluation of the effectiveness and safety of several clinical trials in which cholecalciferol (vitamin D3) [mostly] or ergocalciferol (vitamin D2). In no case does the review collect clinical data generated from calcifediol supplementation, so including calcifediol in the phrase seems to us to generate some confusion.

Actually, the authors' thesis of the cited article is that, based on the scientific evidence available at the date of publication, it could be concluded that 10,000 IU of cholecalciferol/day may be the maximum safety limit for supplementation with vitamin D (it is even said that there is no robust evidence that even higher doses cause severe hypercalcaemia and/or vascular calcifications) and that doses of up to 4,000 IU of cholecalciferol/day are safe, without mentioning anything about calcifediol as an alternative supplementation with vitamin D. We would like to show that we agree with the conclusions of Bischoff-Ferrari et al.² Therefore, we consider that the statement made in the SEIOMM document on vitamin D and COVID- 19 regarding the safety of vitamin D should refer only to cholecalciferol.

López-Medrano F, Costa-Segovia R, Díaz-Pedroche C

Internal Medicine Service. Research Institute i + 12.

University Hospital October 12. Madrid (Spain).

Medical Department. School of Medicine. Complutense University

of Madrid (Spain)