Vitamin D and COVID-19: evidence and recommendations for supplementation

Evidence linking vitamin D deficiency with COVID-19 severity is circumstantial but considerable—links with ethnicity, obesity, age and institutionalization; latitude association; evidence from experimental models of respiratory pathogens; preliminary reports of associations with COVID-19 severity in hospitalized patients; basic biology studies showing extensive vitamin D impacts on the immune system underlying various anti-viral and anti-inflammatory responses; vitamin D responsive genes altered in lung lymphocytes from COVID-19 patients.

Vitamin D deficiency is common; particularly, but not solely, in people living well away from the equator and can persist throughout the year in individuals who have little sunlight exposure.

Vitamin D deficiency is readily preventable by supplementation that is very safe and cheap.

The current UK definition of vitamin D deficiency (less than 25 nmol l−1) is low by international standards and evidence from parathyroid hormone status (which rises with vitamin D deficiency) as well as large population studies of all-cause mortality suggests that a target blood level of at least 50 nmol l−1, as indicated by the American Institute of Medicine and by the European Food Safety Authority, is more appropriate. This would require supplementation with 800 IU/day (not 400 IU/day as currently recommended in UK) to bring most individuals up to the normal range. Growing evidence suggests that regular daily supplementation is more effective than intermittent high-dose bolus.

Vitamin D supplementation at levels needed to avoid deficiency—e.g. 800–1000 international units (25 μg) vitamin D3/day—is extremely safe and typically costs no more than 10p per day.

Randomized placebo-controlled trials of vitamin D in the community in vitamin D-deficient individuals will be difficult to conduct and will not complete until spring 2021 at earliest—although we note the positive results from Cordoba, Spain of an open-labelled randomized trial of 25(OH)D3 (calcifediol) in hospitalized patients.

There seems nothing to lose and potentially much to gain by recommending vitamin D supplementation for all, e.g. at 800–1000 IU/day, making it clear that this is to help ensure immune health and not solely for bone and muscle health.

This should be mandated for prescription in care homes, prisons and other institutions where people are likely to have been indoors for much of the time during the summer.

People likely to be currently deficient should consider taking a higher dose, e.g. 4000 IU/day for the first four weeks before reducing to 800 IU–1000 IU/day

People admitted to hospital with COVID-19 should have their vitamin D status checked and/or supplemented and consideration should be given to testing high-dose calcifediol in the RECOVERY trial.