The link between vitamin D and Covid-19 is complex

“The death rate in Andalucía almost halved following the introduction of their Vitamin D policy. Tragically, here in the UK our death rate more than doubled over the same period, despite us having 5x the vaccinations.”

“This is a very important study on vitamin D and Covid-19. Its findings are incredibly clear. An 80% reduction in need for ICU and a 60% reduction in deaths [...] the study demonstrates that the clear relationship between vitamin D and Covid mortality is causal.”

Vitamin D has been talked about as a potential treatment to prevent Covid-19, or reduce its severity, since the outbreak of the pandemic. This has resurfaced over the past few weeks with the discussion of data from a Spanish public health approach, and a new trial from Spain which looked at vitamin D as a treatment for Covid-19.

Whilst many studies show an association between low vitamin D levels and higher rates or severity of Covid-19, it has been difficult to show low vitamin D to be the cause of higher rates or worse infection. There are a number of interconnected social and physiological factors which make determining low vitamin D levels as the sole cause of increased or worsened infection complicated, and studies often show conflicting results. 

Whilst having vitamin D within a normal range is certainly part of overall good health, which could help the body cope with Covid-19, further randomised control trials are in progress. A study run by Queen Mary University of London, for example, has been designed to offer robust evidence and give a “definitive answer to the question of whether vitamin D offers protection against COVID-19”. 

What has been claimed about Vitamin D?

At the start of February, Conservative MP David Davis tweeted that the death rate in Andalucía, Spain, had “almost halved following the introduction of their vitamin D policy”.  

He also shared a data table and graph showing a reduction in deaths from Covid-19 in Andalucía between November and December 2020, after the supposed introduction of vitamin D supplementation in the region in November. 

Mr. Davis’ office shared his  sources with us. Although the figures we reached were slightly different, data taken from the Andalucía Ministry of Health and Families website for the same period does show a reduction in deaths between November and December 2020 from 194 deaths per million people to 85 deaths per million.

However, deaths then increased again in January to 176 deaths per million of the population. Whilst there is recognition that residents in Andalucía have been given vitamin D supplementation, there is no further detail published on this policy, or evidence of formal trial results. 

There is no clear evidence that this reduction in deaths in November and December is solely due to the introduction of vitamin D supplementation, and it doesn’t explain the upturn in deaths in January. Other potential causes for the reduction in deaths could be the coronavirus restrictions introduced in Andalucía in November. 

Mr. Davis has also tweeted the results of a study from Barcelona, which has not yet been peer reviewed (meaning it is what is known as a pre print), which looked at the impact of vitamin D as a treatment for Covid-19. 

He said the findings of the study are “incredibly clear” in showing an 80% reduction in the need for intensive care treatment and a 60% reduction in death, and added: “Furthermore, since the study demonstrates that the clear relationship between vitamin D and Covid mortality is causal, the UK government should increase the dose and availability of free vitamin D to all the vulnerable groups.”

Whilst the results from this trial sound encouraging, and build on the findings of a pilot study held in Cordoba, it is important to recognise some of the limitations of this data. The pre print does not include information on how they decided which participants to give vitamin D to, and which not to. There could therefore be large differences in the background health and demographics between the group that received vitamin D, and the group that did not. There was also evidence that some trial protocols were not followed. For example 50 patients who were part of the group who were not supposed to receive vitamin D treatment, were given vitamin D on admission to intensive care. 

This study has since been removed from the Lancet website, pending ‘investigation’. Professor Naveed Sattar, Professor of Metabolic Medicine at the University of Glasgow said the trial “falls well short of a well conducted randomised trial. Whilst many wish to believe vitamin D is the cure to Covid-19 or an exciting treatment, this ‘trial’ cannot allow any such inference”.

Another recent study showed no impact of treatment with vitamin D on Covid-19 mortality, need for mechanical ventilation, or length of hospital stay. 

There are several randomised control trials underway, due to be published in 2021. These will give more evidence, to help to answer some of the questions around vitamin D and Covid-19. 

Why the interest in  Vitamin D?

Vitamin D helps to regulate calcium absorption, and bone development. Most of our vitamin D is absorbed from interactions between substances in our skin and sunlight, with a small amount absorbed from dietary intake. 

Studies have suggested that vitamin D serves an important immune function, and it has been implicated in preventing a range of conditions including particular cancers, cardiovascular disease, and severe infections. There has been growing interest in the benefit of vitamin D in prevention and treatment of respiratory infections in particular. A 2020 meta analysis for example, concluded that taking vitamin D supplements reduced the risk of respiratory infection, although only for people aged between one and 16-years-old.  It added that the “relevance of these findings to COVID-19 is not known and requires investigation.”

In addition to this evolving research, it was recognised that Covid-19 has disproportionately affected countries with known vitamin D deficiency, and people who are at higher risk of low vitamin D.

Why the debate?

Some politicians and medical professionals feel that there is a body of evidence, through trials such as these from Spain, Israel and America which show an association between low vitamin D and Covid-19 infection, or show reduced severity of infection with vitamin D treatment. They argue that given the context of a pandemic, and as vitamin D is relatively safe, and cheap, it should be used as part of the toolkit against Covid-19.  

Others, however, feel that the evidence base reveals a more complex picture. Some studies, such as those mentioned above, do show an association and potential benefit. There are also studies however, such as this randomised control trial from Brazil, or this study from the UK, which show conflicting results. The Brazil study, for example, shows no impact from treatment with vitamin D in hospitalised patients, whilst the UK study showed that the association between low vitamin D and Covid-19 may be due to other factors. However, it is also important to note that the Brazil study has been criticised, and faces calls for a retraction, with concerns raised about how reliable and ethical the research was.

Many of the risk factors that cause somebody to be low in vitamin D are also risk factors for Covid-19, including being an older age, from a BAME background or having certain chronic diseases. Therefore it is hard to tease out if it is low vitamin D, or factors causing the low vitamin D that make someone more vulnerable to Covid-19 infections. Whilst it is clear that there is an association between low vitamin D and Covid-19, studies have struggled to definitely remove the impact of other factors, and have often shown conflicting results. 

Another complicating factor is that, as part of a normal inflammatory response, vitamin D levels fall. Therefore whilst vitamin D levels will often be low in someone who is very unwell in hospital, this may be a temporary response to their period of illness, rather than a reflection of the person having generally low vitamin D at the time of becoming unwell. Caution therefore needs to be exercised when vitamin D levels are measured in relation to Covid-19 infection.

Should you take vitamin D?

As we’ve discussed, there is ongoing debate about the role of vitamin D in Covid-19.

The National Institute for Health and Care Excellence (NICE) concluded in December 2020 that there was insufficient evidence to recommend vitamin D as a treatment for Covid-19, or to alter guidance around vitamin D supplementation because of Covid-19. 

The current guidelines from NICE state that everyone over the age of four should: “consider taking a supplement containing 10 micrograms (400 units) of vitamin D daily between October and early March, when people in the UK do not make enough vitamin D from sunlight.” For some clinical groups, such as children age 1-4 years old (and some babies under 1 year old), people with darker skin or little exposure to sunshine, they recommend taking vitamin D supplementation all year round. There are some health conditions that mean that people should not take vitamin D supplements. 

Some medics have suggested that a higher daily dose of vitamin D should be recommended, which would bring the UK in line with EU and US guidance. 

NICE has commented that its guidance will be updated as new evidence becomes available.