Covid-19 Mortality

Vitamin D: it may have helped Donald Trump but what is the evidence?

Amongst the cocktail of old and new drugs pumped into President Trump was vitamin D.  There is no shortage of research with over 200 scientific papers published on the potential role of vitamin D in this disease this year; with much of the evidence emerging in the last few weeks.  In this post I address 2 separate but related questions about this vitamin: (i) does it protect against getting the infection? and (ii) is it useful as a treatment for the infection?  I hope you find the conclusions interesting!

What is vitamin D

  • Vitamin D is a chemical that is found naturally in many foods 
  • By far and away our largest source of vitamin D is our ability to  manufacture it in the body by the action of sunlight
  • Interesting fact is that it is cholesterol that is changed by sunlight to vitamin D, a chemical which is very similar 
  • There are two main forms of vitamin D: D2 and D3 (not sure what happened to D1!)
  • D2 is found in plant oils (and mushrooms)  and D3 is found in animal fats, milk etc.  It is the D3 version that is produced by sunlight
  • Vitamin supplements bought over the counter may contain either D2 or D3
  • Both forms of vitamin D are then converted in the body (in two steps actually: the first in the liver and the second in the kidneys) into the form where it is active  

How much vitamin D do we need?

  • The good news is that vitamin D is stored in the body (in fat tissue) and has a ‘shelf life’ of at least a year, so we don’t need to have vitamin D every day
  • There is a debate as to how easy it is to get all the vitamin D we need from sunlight alone, and of course it depends on how much of the body is exposed and how bright the sun
  • If relying on sunlight, the amount of time needed to get the recommended daily amount of 1000 IU* (stands for international units), varies from 30 minutes to 2 hours
  • You would need to eat 5 cans of tuna to have the same intake!
  • You can have too much vitamin D, very unlikely from diet or sunlight but it is possible if you have an excessive intake of vitamin D supplements

*some have suggested that 400IU is enough

Why do we need vitamin D? 

  • For years the main function of vitamin D was thought to be in giving healthy bones
    • Deficiency in childhood leads to weak bones that fracture, including the disease rickets 
    • Deficiency in adults also affects bones and leads to bone diseases such as osteoporosis
  • We thought that with our knowledge of vitamin D rickets from the Victorian period would have disappeared; it has not!
  • Increasingly it is now known that vitamin D is also needed for the optimum functioning of the immune system and the prevention of inflammation
  • There is some evidence that people who are deficient in vitamin D are at risk of several disorders including heart disease, cancers and some auto-immune diseases
  • Also, well known for years is that vitamin D has a crucial role in the body’s defence against viral infections
  • Prior to the Covid-19 pandemic it had been suggested that vitamin D deficiency could increase the risk of contracting flu in an influenza pandemic, but the data are conflicting 


Who is at risk of vitamin D deficiency?

  • The list is fairly obvious from what we know about the key role of sunlight exposure to produce vitamin D
  • Risk groups are those who do not get sufficient exposure to the sun and include 
    • Ethnic and cultural groups, such as South Asian women and ultra-orthodox Jews, who cover themselves 
    • People who live in overcrowded urban conditions
    • Older people who do not go outdoors sufficiently
  • One concern is that with increasing advice to avoid sunlight to protect against skin cancer the pendulum may have swung too far

How is vitamin D deficiency diagnosed?

  • Given the above it is obviously important to know if someone is vitamin D deficient
  • The only way is to do a blood test, which can be done on a finger prick 
  • It is not necessary for people not  in a high risk group to be tested routinely 

How common is vitamin D deficiency?

  • The rates of vitamin D deficiency are startlingly high in UK and North American cities
  • There ae several studies showing high rates of  more than 50% in residents of care homes (relevant given the outbreaks of Covid-19)
  • Similar high rates are found in elderly people living at home 
  • In many studies in the UK up to  50% of BAME (Black, Asian and Minority Ethnic) groups in England are vitamin D deficient

The evidence that vitamin D is important in Covid-19

There are several questions which can be addressed:

  1. Are people who are vitamin D deficient at increased risk of contracting Covid-19 infection?
  2. Will vitamin D supplements protect against catching Covid-19? 
  3. Are people who are vitamin D deficient at increased risk of having a more serious illness if they contract Covid-19 infection?
  4. How useful are vitamin D supplements as a treatment for Covid-19? 

Are people who are vitamin D deficient at increased risk of contracting Covid-19 infection?

  • The circumstantial evidence is compelling given for example the high rates of transmission and infection in groups known to be at high risk of vitamin D deficiency 
    • Care homes
    • Groups in Western countries living in overcrowded conditions
    • South Asian groups in the Northwest of England
    • Slum areas in India
  • There are some direct data suggesting that this link might be real: a  recent study from Chicago showed that the rate of Covid-19 was twice as high in people who were vitamin D deficient as in those who had normal levels 
  • By contrast a very large population study from the UK (Biobank) did not show a relation between vitamin D levels in the blood and being tested positive for Covid-19.  
  • That study has been criticised on the basis that that the vitamin D was measured in blood samples that were 15 years old

Will vitamin D supplements protect against catching Covid-19?

  • The short answer is ‘we don’t know’!
  • To examine this, we would need very large clinical trials of thousands or tens of thousands either:
    • who had been tested and then, if deficient, randomised to take vitamin D supplements or not.  This is almost certainly unethical
    • general population sample randomised to be given a vitamin D supplement or not, independent of whether they were deficient (ie a similar trial design to testing the value of a vaccine)
  • with then both groups being followed up to ascertain their chances of catching Covid-19.  The logistics of undertaking such studies are formidable 

Are people who are vitamin D deficient at increased risk of having a more serious illness if they contract Covid-19 infection?

  • Again, there is a large amount of circumstantial evidence.  Groups whom we might expect to be vitamin D deficient have much higher mortality risks from Covid-19 including:
    • Elderly people
    • Care home residents
    • Those South Asian and other communities that have less sunlight exposure
  • The ‘cytokine storm’, the body’s over-reaction of its entire immune system to infection which has been considered responsible for a high proportion of Covid-19  deaths, may be related to vitamin D deficiency 
  • A study in Italy showed that the chances of having a bad respiratory illness if admitted with Covid-19 was increased in those with vitamin D deficiency 
  • Similarly, a study last week from the UK found a threefold increase in the risk of being admitted to ICU if the patient was vitamin D deficient

How useful are vitamin D supplements as a treatment for Covid-19?

  • In a Lancet medical journal article in August, the case was put forward for undertaking clinical trials of  using vitamin D as a treatment.  Such clinical trials are now underway
  • The first trial has now been reported from Spain.  It was not the greatest clinical trial in terms of its quality and more information is needed but:
    • Of the 50 patients randomised to receive vitamin D only 1 needed admission to ICU
    • Whereas of the 26 patients randomised to receive placebo, 13 needed admission to ICU
    • It is not known if these patients were deficient in vitamin D before they became infected
  • And then of course there is Donald!


  • From a public health perspective, even before the Covid-19 pandemic, there is overwhelming evidence that there are unacceptably high levels of vitamin D deficiency in some population groups
  • These groups are the same as those who have more Covid-19, and more serious outcomes if they catch the disease
  • There is no evidence, nor does it seem likely, that for people who are not deficient taking extra vitamin D would protect against catching Covid-19
  • More clinical trials are needed to see if vitamin D is useful as a treatment both in the general population and more usefully in those who are deficient 
  • At the very least those who are diagnosed with Covid-19 infection should have their vitamin D levels measured

If you would like to receive email notifications of new posts on this blog just click this link and enter your email at the bottom of the home page: