Public Health England is recommending people consider taking daily vitamin D supplements throughout the spring and summer as the coronavirus lockdown continues. This is a piece of good news! Some vitamins and minerals are vital role to our health. Particularly important at the moment, we need to think how vitamin D affects our immune system


So what is vitamin D?

Vitamin D is often called the ‘sunshine vitamin’ because it is produced by the body when we expose our skin to the ultraviolet from the sun. It is actually a prohormone (it is a compound that can be transformed into a hormone by the body) and is the only vitamin that our body can produce (1).

We get most of our vitamin D from our skin, but you can also find some vitamin D in food such as egg yolk, sardines, cod liver oil, salmon…. (2)




%RDA (Recommended Daily Allowance)

Cod liver oil, 1 tablespoon


Trout (rainbow), farmed, cooked, 3 ounces


Mushrooms, white, raw, sliced, exposed to UV light, 1/2 cup


Sardines (Atlantic), canned in oil, drained, 2 sardines


Egg, 1 large, scrambled (vitamin D is in the yolk)


Liver, beef, braised, 3 ounces


Tuna fish (light), canned in water, drained, 3 ounces




Vitamin D has several functions in the body. It helps absorb calcium and phosphorus, which are essential for bone health. Without enough vitamin D, bones can become brittle and out of shape as it is the case in rickets, a severe form of vitamin D deficiency or osteoporosis. It supports the immune system and has some effect on the cardiovascular system and high blood pressure. It is also associated with cancer rates, autoimmune diseases such as MS and energy production (3) (4). An estimated 20-50% of many diseases could be prevented by adjusting vitamin D.


Vitamin D deficiency is common!

It is estimated that up to 40% of people in the UK are deficient in vitamin D (5), with ethnic minorities and the elderly more affected.  In the UK, the sun is too low on the horizon between October and March for the body to produce vitamin D. This and the increased use of sunscreen and spending less time outdoors might explain why we tend to be low in vitamin D. Indeed, these have been touted as the reason for the increase in rickets cases in the UK. Because optimal vitamin D levels are critical to overall health, ensuring that you are not deficient is essential.

Vitamin D levels vary during the year and are their lowest around February. Because the vitamin D you get from food is usually a small part of what you need and we have less sun during the winter, our reserves go down. This is the reason why the NICE guidelines encouraged some populations to have some vitamin D supplementation between October and March. Severe deficiency in vitamin D is defined as a concentration in vitamin D below 30nmol/l, and deficiency is defined as a concentration below 50nmol/l.


Vitamin D affects our immune system


Multiple studies have shown a link between vitamin D and a healthy immune response. It has been shown to support both the innate and the adaptative part of our immune system.

The innate immune system is the part of our immune system that reacts against any invasion and is very much our first line of defence. It doesn’t differentiate between the pathogens and is our first line of defence and includes physical barriers such as the skin, the lungs or the inside of our nose. This part of our immune system also consists of some specific cells that attack any foreign cells in the body.

The adaptive immune system is also called the acquired immune system and is our second line of defence. It is composed of cells that attack specific pathogens. It is a much more complicated system, and it can take days or weeks to produce the cells specific to a pathogen. These cells are called T cells and are a type of white blood cell. It can remember the pathogens too so if you are infected by the same pathogen again, the immune response is more efficient.

Vitamin D plays a role both in our innate immune system, our first line of defence and in the more complex adaptive immune system.


The First line of defence (7):

Vitamin D helps support our immune system in 3 ways:

1- Vitamin D strengthens our physical barriers against pathogens, especially in the gut and in the lungs. This is especially true for the cells inside our lungs when we are under attack from a viral infection. It also increases the production of antibacterial compounds.

2- Vitamin D is needed by some white cells to help them recognise and destroy pathogen in the body

3- Vitamin D supports the gut microbiome. About 80% of all the immune system is in the gut, and the health of our gut bacteria influences the way our immune system reacts. A healthy gut flora supports a healthy immune system.

The Second line of defence (8):

The adaptive immune system is complex. For the white blood cells to be able to neutralise a pathogen, they need to go through several steps. Those T cells need to be activated. They also need to differentiate/transform into a different type of immune cells (which then leads to a different kind of response from the immune system).

Vitamin D is involved in the immune system in 4 different ways:

1- Vitamin D activate T cells so they are better able to respond to a pathogen

2- Vitamin D influences the T cells differentiation/transformation

3- Vitamin D helps some white cells to mature and modulate the immune system for better efficiency

4- T cells respond directly to vitamin D by producing specific white cells



What about the current epidemy?


There hasn’t been any finalised research yet about the influence of vitamin D and the Coronavirus. Some studies are under the way in France and in Spain. However, preliminary results from Southern Asia show that there might be a strong link between the severity of the disease and the level of vitamin D.

In particular, 86% of all cases with normal vitamin D levels were mild, whereas 73% of cases with low vitamin D levels were severe or critical. This goes a long way to explain the advice from Public Health England.


Vitamin D levels affects the immune system

Click to enlarge (from GrassrootsHealth Research Institure)


How much vitamin D should you take?


This really should depend on what your level of vitamin D is.

The NHS has updated its advice, saying that everyone should consider taking 10µg (400IU) per day during the whole of the summer. This is around half of your daily requirement of vitamin D.

If you are deficient or if you do have the opportunity to go outside much, a higher dose might be more suitable.1000 IU to 2000IU would be suitable for most people. Be mindful not to overdose on vitamin D. The maximum daily dose is 4000IU (unless prescribed by your GP). Vitamin D supplements are quite easy to find. If you are considering buying some, you need to ensure that the vitamin D is vitamin D3 as it is the one most usable by the body. You will find it in tablet form or drops. Just chose whatever works best for you.

If in doubt about dosage, contacting a nutritionist for advice would be best so you can have the most appropriate dosage for you.

Last but not least, remember to go outside, without sunscreen and uncovering legs and arms. This will allow your body to manufacture its own vitamin D and is safe as long as you are also mindful of not getting sunburnt.


You might also be interested in:

Why feeding your gut flora is the best thing you can do for your health right now

The emotional toll of the Coronavirus