Vitamin D – Everything You Need to Know

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What is vitamin D? How do you get it? Why does it matter? We talk all things vitamin D with Dr Andres Maldonado.

In a Nutshell

The quick Version

What is Vitamin D?

It's a vitamin we get from both food and sunlight which affects a number of functions in our body.

What Causes Vitamin D Deficiency?

Inadequate exposure to the sun has a part to play. But also, diseases of the small intestine and kidney diseases and genetic disorders can cause deficiencies.

Should we Supplement Vitamin D?

UK guidance does state that some supplementation, particularly over the winter months, is recommended.

What is Vitamin D?

Vitamin D is a “fat soluble” vitamin. In simple terms, what this means is that it can be absorbed with fats in food and stored in fatty tissue and the liver.

It also known as “Calciferol.”

Vitamin D plays some really crucial roles in the body including regulation of our calcium levels, cell growth, our metabolism and our immune systems. So this vitamin really is important to our general health.

Where do we get vitamin D from?

We get vitamin D from both sun exposure and from diet.

When the skin comes into direct contact with sunlight, it is able to “synthesize” vitamin D (in a process known as “skin synthesis”). Exposure to direct sunlight is the most important way in which we get vitamin D.

In our skin, there is a molecule called 7-dehydrocholesterol and when it comes in contact with UV rays it undergoes a reaction that causes the transformation into Vitamin D3. This system is incredibly efficient and it is estimated that brief casual exposure of the arms and face to sunlight is equivalent to ingestion of 200 units of vitamin D per day.

This process is influenced by skin type, latitude, season, and time of day.

In the UK, for example, sunlight can be something of a rarity at times!

Vitamin D Rich Food Sources

Although sun exposure (and skin synthesis) is the primary way in which get Vitamin D, there are some food sources that Vitamin D rich.

They include:

  • Oily fish such as salmon, sardines and mackerel
  • Vitamin D fortified foods like breakfast cereals

In reality, however, it can be tricky to get enough vitamin D from diet alone.

What causes vitamin D deficiency?

There are multiple causes that of vitamin D deficiency. Amongst the most significant:

  • Deficient intake or absorption. This could simply be caused by not eating enough vitamin D rich foods. But also, this can be caused by conditions in the body like diseases of the small intestine, gastric bypass or other malabsorption diseases that simply stop your body from absorbing vitamin D well enough even if you’re eating vitamin D rich foods.
  • Inadequate sunlight exposure. Simply not getting enough sunlight exposure is a very common cause of Vitamin D deficiency, particularly in places like the UK and over winter time.
  • Others medical conditions and medications can also cause vitamin D deficiency. They include anticonvulsants, kidney diseases, genetic disorders and others.

What are the symptoms of vitamin D deficiency?


Being deficient in vitamin D can also mean your body struggles to absorb enough calcium. So a vitamin D deficiency can be responsible for symptoms associated with low calcium levels.


In children, it is presented as rickets that can have varying degrees of pain and irritability, motor delays, and poor growth. Younger children may manifest with delayed closure of skull, widening of wrists and ankles, and bow legs or knock knees.


People who are in the risk group for vitamin D deficiency are breastfed infants, pregnant women, older adults, people with dark skin, people with intestinal disorders, obese people, people with bariatric surgery, people with osteoporosis, among others.

Other common symptoms associated with vitamin D deficiency include:

  • Fatigue and lethargy
  • Bone pain
  • Muscle weakness or even muscle aches and pains
  • Mood swings and mood changes

How do I test for a Vitamin D deficiency?

You can go to your GP who will carry out a blood test for you. Or if you’d rather take a vitamin D test at home, Cerascreen offer an at home finger prick test.


It’s a very straightforward test.

Should we take vitamin D supplements?

Guidance actually varies depending where in the world we are. And the quantity you might be recommended can vary based on age and genders amongst other things.

The NHS has strongly recommended a vitamin D supplement to everyone this year, with this piece of advice on its website:


It's important to take vitamin D as you may have been indoors more than usual this year. You should take 10 micrograms (400 IU) of vitamin D a day between October and early March to keep your bones and muscles healthy. There have been some reports about vitamin D reducing the risk of coronavirus (COVID-19). But there is currently not enough evidence to support taking vitamin D to prevent or treat coronavirus.

Where can I get vitamin D supplements?

Vitamin D supplements are widely available. You can get a whole year’s supply for under £10 so this shouldn’t and needn’t be an expensive supplement.

Vitamin D and Coronavirus 

There have been several claims over the past few months about vitamin D and its potential to reduce the chance of severe Coronavirus.

As yet, there is no conclusive study.

But we do know that Vitamin D does help the immune system to perform at optimum level and is therefore beneficial to staying well on the whole.


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