• Victoria Purdon

Vitamin D - the What, Why and How

Updated: Jan 11

We have been hearing a lot about vitamin D in the news in terms of Covid studies and immune boosting. But if you are anything like me, then you need to know the why. You're in the right place if you want to know more about this vitamin ( that isn't necessarily a vitamin - as it is synthesised in the skin!)


Did you know there are two types of Vitamin D?

Vitamin D2: this comes from plant sources

Vitamin D3: this comes from animal sources.


About D2

Plants contain a provitamin of vitamin D called ergocalciferol. When ergocalciferol is exposed to sunlight, it converts into D2. Think of hay left in the sun before it is fed to livestock- this is how cows get their Vitamin D.


About D3

In animals, cholesterol is converted to 7-dehydrocholesterol which is a provitamin of D3. When 7-dehydrocholesterol is exposed to sunlight ( in the skin) it converts to cholecalciferol ( Vitamin D3).

Two main take aways here are :

  1. Having good cholesterol is important for conversion pathway

  2. Sunlight is important for converting these provitamins to whole vitamin forms.

What does Vitamin D do?

Vitamin D isn't as straight forward as other vitamins, in that it doesn't have a direct effect on the body in its whole form. It needs to be hydroxylated before it can be used. Vitamin D is synthesised from sun to skin to the liver and kidneys. It is important that all of these organs are supported with a healthy whole food diets to carry this pathway out, which is why I am always talking about a whole food diet! Without properly functioning systems, vitamins may not get effectively converted. Through this process, it is converted into a hormone, which is beneficial for our brain, immune system and bone health to name a few.


How do I get Vitamin D?



There are three options:

1. Sunlight

Trans-dermal ( through the skin) is the most effective way for the body to get vitamin D. Studies show that even 10-30 minutes a day can be effective. However note that if your shadow is longer than your body than the sun isn't strong enough for vitamin D synthesis. I talk more about the importance of this for our health in this post on sunlight, sleep & SAD.


2. Diet

If sun exposure is insufficient, like in the winter months, dietary vitamin D can help increase our levels. Foods highest in D3 are oily fish. Vitamin D is a fat soluble vitamin, which means fats need to be present when consumed to cleave the nutrient for the body to convert and absorb. Very conveniently oily fish are a perfect package for this (amongst many other benefits!)

If you are on a very low fat diet, you may have trouble absorbing vitamin D.


Some high vitamin D foods:

- Sardines

- Salmon

- Butter

- Eggs

- Liver

- Mushrooms


3. Supplements

As most of us are deficient here in the UK, through the winter it is safe to take up to 5,000iu daily. However, always, always test before you dose higher. As Vitamin D is fat soluble, it can be stored in our body. If we have too much, Vitamin D toxicity can occur. From exogenous sources ( food and sunlight) toxic levels are unlikely, but when supplementing, testing is always advised.

This is fairly inexpensive too!


If you are looking to supplement through the lower months, you'll want to look for a supplement that is D3 ( as we have learnt this is more potent than D2) combined with vitamin K2. These work synergistically to enhance absorption and boost our immune systems. Personally, I like Better You's spray, or under the tongue drops, as these bypass the gut and so any gut absorption issues are avoided.


Did you learn something new from this? Let me know in the comments!

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