Coronavirus and vitamin D — what do we know?

Megan Widdows
Written by

Megan Widdows

3rd February 2021

There’s been an ongoing debate amongst scientists over whether there’s a link between vitamin D and coronavirus (COVID-19).

Many now believe that vitamin D supplementation could be a useful, protective tool in the fight against the coronavirus pandemic.

In fact, in December 2020, the UK government received updated advice from Public Health England (PHE) and the National Institute for Health and Care Excellence (NICE). After this, they began offering a free 4-month supply of vitamin D supplements to people who are considered clinically extremely vulnerable.

But what evidence is there to support this? This guide looks into the latest research and advice from our leading health bodies to dig deeper into this uncertain topic.

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The role of vitamin D

Vitamin D is one of our essential vitamins and has many functions in the body. Its main job is helping to build and maintain a healthy skeleton by keeping the levels of calcium and phosphorus in our blood at just the right amount. Other roles include supporting our metabolism, muscle health, and nervous system.

Vitamin D is also important to our immune system, which helps us to fight off infections.

Sources of vitamin D from food are relatively scarce but include oily fish, liver, red meat, and fortified foods such as some kinds of margarine and breakfast cereals. Instead, the main source of vitamin D is the Sun.

When our skin gets exposed to the Sun’s ultraviolet rays, a chain of reactions begins. This triggers our body to produce many helpful chemicals. One of these is vitamin D. Vitamin D can then move around the body, carrying out its many roles in maintaining our health.

Key points:

  • Vitamin D is an essential vitamin with many important functions in the body
  • There are few dietary sources of vitamin D, so our main source is Sunlight

How common is vitamin D deficiency?

The main source of vitamin D is Sunlight. Rates of deficiency increase as we travel away from the equator, where the Sun’s rays are the strongest.

Similarly, vitamin D deficiency is much more common in the winter, compared to the summer months. During summer, it’s more likely to be sunny, and people spend more time outdoors. This means we tend to get enough sunlight to maintain healthy vitamin D levels.

One study found that, in the UK, our vitamin D levels are around 50% lower in February compared to September. This means we are more likely to become vitamin D deficient.

Factors that increase the risk of developing vitamin D deficiency include:

  • old age
  • regular use of suncream
  • darker skin
  • spending little time outdoors
  • wearing clothes that cover all or most of the body

Similarly, the time of day a person is outdoors, the distance from the equator, and the time of year all play significant roles.

The NHS considers a blood concentration of vitamin D that’s lower than 30nmol/L to be deficient and levels between 30-80nmol/L insufficient.

At least 1 in 5 adults in the UK are deficient in vitamin D. More people are likely to fall into the insufficient category.

Deficiency can have serious health implications such as increasing the risk of developing bone diseases, certain cancers, type 2 diabetes, and high blood pressure.

Key points:

  • Vitamin D deficiency is really common, affecting at least 1 in 5 UK adults
  • Deficiency is most common in the winter, and in places that are further from the equator where the Sun’s rays are weakest

Can vitamin D help our immune system?

Vitamin D helps our immune system, our way of fighting off viral and bacterial infections. A deficiency of vitamin D may impair its function, leaving us more susceptible to infections. Some scientists strongly believe that taking a daily supplement of vitamin D can prevent acute respiratory infections to some degree.

A recent meta-analysis (research that combines the findings of multiple studies) found that there were significant protective effects associated with supplementing vitamin D.

The patients who received a daily or weekly supplement of vitamin D had a slightly lower risk of contracting a respiratory infection than patients who didn’t.

Additionally, the supplemented patients were 17% less likely to require hospital treatment for their infection, suggesting they experienced a less severe illness. Most importantly, the patients who received the supplement were 30% less likely to die from a respiratory infection than those who didn’t.

The researchers also found that daily and weekly doses of vitamin D were the only methods that offered protection. Larger doses delivered monthly didn’t offer any protection from respiratory infections. Similarly, if the patient already had optimal vitamin D status, there were no additional benefits to supplementing.

This offers important insight into the role that our vitamin D status may play in our risk of developing and recovering from respiratory infections. However, other studies have failed to identify this same protective effect. Questions remain over the full effect of vitamin D deficiency on immunity.

It’s important to remember that supplementation of vitamin D only offers small, though significant, benefits that may take months to develop, especially if you’re already very deficient.

Key points:

  • Vitamin D plays an important role in supporting our immune system
  • Studies have shown that supplementing vitamin D can reduce the severity and risk of dying from respiratory infections

What about Vitamin D and coronavirus specifically?

COVID-19 is a respiratory infection with a large range of symptoms. For some, infection is asymptomatic or results in mild illness. Yet others become severely ill and require hospital treatment.

Of these hospitalised COVID-19 patients, between 20-40% develop a life-threatening condition called acute respiratory distress syndrome (ARDS) and require intensive care treatment.

Studies show that as we travel further from the equator our risk of dying from coronavirus increases. Even when we adjust for having older populations, higher population densities, and different levels of pollution.

We also know that as we travel further from the equator our risk of developing vitamin D deficiency increases. This link meant that scientists believed there could be a link between low vitamin D levels and our risk of dying from coronavirus.

The factors that we already know to put you at high risk from coronavirus disease include:

  • old age
  • black and Asian ethnicities
  • diabetes
  • obesity
  • high blood pressure

Interestingly, these are also associated with an increased prevalence of vitamin D deficiency.

This supports the idea of a link between vitamin D deficiency and coronavirus. However, it’s not yet possible to know whether one directly influences the other.

Instead, the overlap between the risk factors for coronavirus and vitamin D deficiency could perhaps be explained by the ‘healthy user effect’. Healthier people tend to spend more time outdoors and eat more healthily than less healthy individuals.

This simultaneously lowers their risk of vitamin D deficiency and lifestyle diseases such as type 2 diabetes and high blood pressure, lowering their risk for severe COVID-19.

Key points:

  • There is a significant overlap between the risk factors for vitamin D deficiency and the factors that make a coronavirus infection higher risk
  • There is some evidence to support a link between supplementing vitamin D deficiency and a lower chance of dying from coronavirus

What’s the latest research?

Several recent studies have tried to identify a link between vitamin D and coronavirus. One of these was a randomised controlled trial that took place in Spain. It was a small clinical trial that compared the use of vitamin D against the outcomes of people hospitalised for COVID-19.

The researchers explored whether early treatment with vitamin D could reduce the need for intensive care treatment, and the risk of dying.

Again, it found that vitamin D seemed to protect patients against the worst of COVID-19. For patients who didn’t receive the supplement, 50% became severely ill and required intensive care treatment. Two patients died. For the patients treated with vitamin D, just 2% required intensive care. No one died.

At first glance, this information seems to suggest that supplementation with vitamin D offers protection against coronavirus. However, when we look closer, the study has some limitations.

It was a small sample size and there were differences in the medical histories and comorbidities between the two groups. Most importantly, the study didn’t record the BMI of the participants, leaving obesity, a major risk factor, unaccounted for.

These findings help us to understand the role of vitamin D in coronavirus infection. Unfortunately, though, there are still lots of unanswered questions.

A review paper, published in November 2020, dug deeper into the research. It examined data from 13 coronavirus-specific clinical trials.

The findings showed a clear link between vitamin D deficiency and either catching, becoming seriously ill, or dying from COVID-19. This suggests that everyone at risk of deficiency could reduce their coronavirus risk by taking a vitamin D supplement.

As this is an ongoing situation, further research and clinical trials are necessary. However, evidence to support using vitamin D supplements against respiratory diseases such as COVID-19 is growing.

Key points:

  • A small clinical trial found vitamin D supplementation to reduce the need for intensive care and the risk of dying from coronavirus
  • A review paper found a strong link between supplementing vitamin D and better COVID-19 outcomes

Should I supplement vitamin D?

The NHS currently recommends everyone takes a daily dose of 400 IU. However, recent research suggests that nearer 1,000-2,000 IU is necessary to maintain healthy levels of vitamin D.

Doses of up to 5,000 IU might be required if you are deficient. There’s little evidence to show that even high-doses of up to 10,000 IU are toxic, but few people need more than 4,000 IU per day.

Studies suggest that the vitamin D3 form is more effective than D2 for raising and maintaining serum levels of vitamin D. So if you buy supplements, look for the D3 type.

Vitamin D is widely available online and from most pharmacies. If you are unsure if this is appropriate or how much you need, please ask your GP for advice.

Key points:

  • Everyone should take a vitamin D supplement, especially during the winter months
  • The NHS recommends 400 IU, but a daily dose between 1,000-2,000 IU may be better suited to maintain healthy levels

Take home message

  • Unfortunately, we still can’t be totally sure of any link between vitamin D and coronavirus but there are strong indications that there’s an association.
  • Taking a daily vitamin D supplement is recommended by the NHS and UK government during the winter to maintain healthy bones, regardless of the coronavirus pandemic.
  • Now more than ever, with limitations on outdoor activities, we need to make sure we are getting enough vitamin D.
  • Studies have shown there is no harm in taking a vitamin D supplement.
  • Instead, supplementation can improve your bone health, sleep quality, and immune system.
  • It may also reduce your risk of severe illness with coronavirus and other respiratory illnesses; plus lowers the risk of developing high blood pressure, type 2 diabetes, and at least 15 different cancers.


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Write a response


9 February, 2021

I found the article informative and will be getting some vitamin d3 when I go shopping.I gout for a walk most days only stopping in when the weather is is too bad.

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