COVID 19 Healthcare Challenge – can vitamin D help to prevent COVID-19?

26th October 2020 by Lisa Greenwood

Vitamin D has been in and out of the news recently. The UK's Secretary of State for Health and Social Care Matt Hancock announced as recently as the 15th October that the government will be stepping up its messaging around promoting vitamin D as potentially boosting resilience to coronavirusThis would suggest that there is evidence to support this. But is there?

Current advice

Pre-pandemic, people living in the UK were advised by official NHS guidelines to supplement their Vitamin D intake between the months of October and March, due to there being not as much sunlight for our bodies to convert.


Overlapping factors

Factors such as being older and being of black and/or Asian minority ethnic (BAME) origin give COVID-19 and vitamin D deficiency some common ground, and scientists have been looking into this. Whilst there is a correlation between vitamin D deficiency and the BAME population, who are also at a higher risk of COVID-19, there is not sufficient evidence of causation at the time of writing.


How it could be effective in protecting against COVID-19

For several years, it has been suggested that vitamin D may be useful in preventing acute respiratory infections, and there is some evidence to suggest this: but results have been inconsistent – whilst there are studies showing a reduction in infection with vitamin supplementation, some have conversely shown no significant difference.


Why the renewed interest?

Several UK newspapers have quoted recent studies specifically questioning whether vitamin D could be beneficial in reducing the risk of COVID-19.  It’s worth taking a look at these studies to see what they actually tell us:

Castillo et al, “Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study”1

Quoted by as showing  “that a high dose of a Vitamin D drug significantly reduced the need for ICU treatment of coronavirus patients” (accessed: 15th October 2020).  Whilst this is what was concluded, there are a few things to note:

  • Type of trial: It is generally accepted that double-blind placebo trials give the most robust results. Whilst this study was randomised, no placebo was administered. 
  • Sample size: the study had 76 participants, all already at the hospitalisation stage of covid-19.
  • Risk factors: Major risk factors, such as obesity, were not included in the field of this study.

Kaufman et al, SARS-CoV-2 positivity rates associated with circulating 25-hydroxyvitamin D levels2 reports that “Dr Michael Holick, a vitamin D expert from the US, recently published a study which found good vitamin D levels can reduce the risk of catching Covid-19 by 54%.” (accessed 26th September 2020).  This was also picked up by Sky News, and the Independent newspaper, amongst others. On closer inspection, whilst Dr Holick may have made this conclusion, the media response is to a different study that Dr Holick was involved in (and was corresponding author).  This study is being cited by the media as potentially proving the efficacy of vitamin d in reducing covid cases.

Once again, there are important factors to take into consideration, which have been formally raised as Expressions of Concern:

  • Sample size: As above, this was a small sample size (235 patients from a database of 611).
  • Diagnosis: Although all patients in the study are listed as having covid-19, just under a third of participants had appositive diagnosis from a RT-PCR test (the gold standard in testing).
  • Risk factors: Factors such as smoking and socio-economic status, were not included.
Where does this leave us?

There is, at this time, no significant evidence to suggest that vitamin D will protect specifically against COVID-19, and more research is needed in this area. There are currently 57 trials  involving COVID-19 and vitamin D registered to take place around the world, including one by Barts Medical School, starting soon. The trial, lasting six months, aims to bring clarity to the question of whether vitamin D really can prevent COVID-19.


What we know for sure is that vitamin D is vital to keeping us healthy, by helping to regulate calcium and phosphate in the body3.  Due to the lack of sunlight between October and March, it is recommended that people in the UK take a vitamin D supplement.  But a word of caution: too much could be harmful, so it is advised to stick to 10mg a day.


For more information on vitamin D, go to the NHS website:


  1. Entrenas Castillo M, Entrenas Costa LM, Vaquero Barrios JM, et al. "Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study". J Steroid Biochem Mol Biol. 2020;203:105751. doi:10.1016/j.jsbmb.2020.105751
  2. Kaufman HW, Niles JK, Kroll MH, Bi C, Holick MF (2020) SARS-CoV-2 positivity rates associated with circulating 25-hydroxyvitamin D levels. PLoS ONE 15(9): e0239252.
  3. Coulston AM, Boushey C, Ferruzzi M (2013). Nutrition in the Prevention and Treatment of Disease.Academic Press. p. 818. ISBN 9780123918840Retrieved 26 October 2020.