Spotlight: How is Vitamin D linked to COVID-19?

  Nell Team
Immunity Nutrition Science Vitamin D

Is there another health crisis ahead of us?

This is one we’ve known about for a while.

Vitamin D deficiency.

This nearly universal nutrient deficiency has not yet been declared a global public health issue, although over one billion people suffer from it.

Lack of vitamin D has always been associated with poor bone health. However, there’s been a resurgent interest in this essential vitamin within the scientific community as more and more research is unveiling the abundance of functions it has, including potential links to the coronavirus.

Before delving into its relationship with COVID-19, let’s rewind back to the basics of the sunshine vitamin.

What is Vitamin D?

Vitamin D is an essential nutrient required for normal cell function. It is not just a vitamin, it’s also a fat-soluble steroid hormone.

Our bodies either synthesise vitamin D in the skin when exposed to UV light from the sun (hence why it is often known as “the sunshine vitamin”) or absorb it from foods, such as fatty fish and egg yolk. Its content in foods is quite low, so our bodies rely on the sun for 50-90% of the vitamin D required. According to the Endocrine Society, the optimal level of vitamin D is 30-60 ng/m. Unfortunately, our lifestyles are at odds with our production of the sunshine vitamin - we wear clothes, we use sunscreen, we work indoors or we don’t get enough sunlight where we live - meaning that we rarely reach the optimal levels.


Mapping Vitamin D to Health

As recent evidence suggests, vitamin D is necessary for more bodily functions than we previously thought.


It’s been drilled into us that milk and other dairy products work wonders for good bone health. That’s because of calcium. Calcium is essential for bone strength. One of the most important roles of vitamin D is in calcium homeostasis. Simply put, it increases calcium absorption from the intestine. This ensures that bones have sufficient mineral density and reduced risk of osteoporosis or bone fractures.


Cancer is essentially uncontrollable cellular proliferation, and vitamin D inhibits cellular proliferation. Studies have shown that those with lower levels (below 30 ng/mL) of vitamin D had almost 2x the risk of colon cancer than those with higher levels. We can see the difference geographically as well. Epidemiologists have found that breast and ovarian cancer mortality rates were lower in sun-filled areas and higher in areas with low sunlight, suggesting that the sunshine vitamin played a preventative role.


Another function of vitamin D is modulating human immune responses. Deficiency in this vitamin is associated with increased autoimmunity and increased susceptibility to infection. Vitamin D receptors are found on immune cells, meaning that once vitamin D binds to the cell, there is an enhanced expression of antibacterial proteins which destroy the bacterial pathogens. Low levels have been linked to tuberculosis, multiple sclerosis and Type 1 diabetes.

Respiratory Infections

There is mounting evidence that Vitamin D plays an unexpectedly important role in respiratory infections, such as tuberculosis, the common cold and chronic obstructive pulmonary disease. Low levels were associated with poor lung health, bronchitis and asthma. Although the experimental evidence has been relatively inconsistent, researchers attribute this preventative capability of vitamin D to its ability to enhance the phagocytic activity of macrophages, a type of white blood cell. Providing vitamin D supplementation has been helpful in reducing risk of respiratory infection by 50%.

What Does This Mean for COVID-19?

It’s common knowledge that being infected with the coronavirus can lead to respiratory issues. Seeing its role in respiratory infections, it seems that “Vitamin D might be ultimately proved to be a crucial factor in reducing susceptibility to lung injury due to COVID-19” as famed American biochemist Dr. Rhonda Patrick believes.

The entry receptor for SARS-CoV-2, the virus behind COVID-19, is ACE2. Once the SARS-CoV-2 virus binds to the ACE2 receptor, it is able to enter the human host cell and infect it, making us sick. The issue is that SARS-CoV-2 binds to a large number of ACE2 receptors, which has grave health consequences. ACE2 is crucial for protecting against acute lung injury and has preventative traits against heart disease. So, the binding of SARS-CoV-2 reduces the ACE2 level on lung cells and thus increases lung damage.


ACE2 is also involved in the renin-angiotensin system as a regulator. This system controls blood pressure, inflammation and body fluid homeostasis. Reduction in ACE2 levels due to the binding of SARS-CoV-2 upsets the balance of the renin-angiotensin system, leading to inflammation and lung injury. This lung injury, if severe enough, stimulates kidneys to release renin, an important enzyme in the renin-angiotensin system, which further decreases ACE2.

How vitamin D comes into play is that it boosts ACE2 levels and provides protection against lung injury. Having insufficient amounts of Vitamin D leads to overexpression of the enzyme renin, which reduces the level of ACE2. In patients with acute lung injury, vitamin D supplementation normalizes ACE2 levels, bringing them up to the required amount.

One omnipresent risk factor for vitamin D deficiency, and hence potentially COVID-19, is genetic variation. If we have a specific type of genetic polymorphism (i.e. have a certain genetic variation) on the CYP2R1 gene or the GC gene, evidence shows that it would increase the risk of vitamin D deficiency. Polymorphisms in these two genes significantly impacts the body’s ability to bind to, convert and absorb vitamin D. At Nell, we study the variations on these genes in our tests.

How Can I Protect Myself?

Although the link between COVID-19 and vitamin D is still classified as potential, preventative measures to risk populations are likely to be more helpful than harmful. And, with lockdown blunting our normal summer rise in vitamin D levels, we have to be even more aware of it.

  • Increase Sunlight Exposure - Aim to get 10-30 minutes of early day or midday sunlight several times a week. Although it is one of the best ways to produce this vitamin, too much sunlight can increase risk of skin cancer. If you know you are going to be outside in harsh sunlight for long, thoroughly apply sunscreen.
  • Consume Vitamin D-Rich Foods - Fatty fish, egg yolk and fortified foods (like soy milk) have good amounts of vitamin D. Incorporate them into your diet to maintain sufficient vitamin D levels.
  • Supplements - This is an effective way of ensuring you have the right amount of vitamin D. Ensure that you take a dosage recommended by a medical professional. Two supplement brands we like at Nell are Nordic Naturals and Wild Nutrition.

Interested in finding out if you have the CYP2R1 or the GC genetic variation for low vitamin D levels? Find out more about our genetic tests at Nell.