Vitamin D supplementation and COVID-19 disease: safety but unproven efficacy-reply to Dr Helga Rhein.

To the editor:

We read with interest the letter from Dr Helga Rhein, responding to our rapid evidence review around vitamin D and COVID-19 disease [1]. Dr Rhein suggests that the “evidence for the benefits of avoiding vitamin D deficiency during the pandemic far outweighs the theoretical risk of overdose” [2]. Thus, “on the balance of probabilities”, should we routinely supplement the population with higher dose vitamin D than the 400 IU/day suggested in the UK as the (dietary) RNI [3]? We completely agree with Dr Rhein that 400 IU/day will not effectively ameliorate overt vitamin D deficiency. If an individual presents with symptoms and signs consistent with the metabolic consequences of vitamin D deficiency, then clearly they should be treated appropriately with more rapid replenishment [4, 5]. This is a fundamentally different scenario to that of population health. The UK Scientific Advisory Committee on Nutrition (SACN) recommendation is aimed at ensuring that 97.5% of the population have 25(OH)D > 25 nmol/l [3]. Whilst one can argue that the therapeutic window for vitamin D supplementation is wide and risks of overdose low, we are not convinced (see our response to the letter of Dr William Grant [6, 7] that this is sufficient reason to introduce population-level higher dose supplementation for prevention of COVID-19 disease when the observational evidence provides very limited support and the best conducted intervention study to date suggests no benefit [8]). Whether such an approach might be warranted for other outcomes, or to prevent metabolic bone disease in high risk demographics, are separate questions.