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Vitamin D: What it does and where to get it

Vitamin D is one of the most important vitamins our bodies use. It is a vitamin but functions as pro-hormone, and deserves a lot of attention. The full scope of vitamin D is beyond what I will share here.

What this post will do is highlight what vitamin D is, it's role in our body, and what foods we can eat to obtain it in our diet.

What is vitamin D

You may remember from my post on vitamin A, that vitamin D is fat-soluble vitamin. That means that vitamin D is best absorbed with the help of fat in the diet, and can be stored in the liver and fat tissue for later use.

Vitamin D has two forms depending on how you obtain it from your diet.

The type of vitamin D you get from consuming animal products is cholecalciferol, also known as vitamin D3. While the type you will get if you consume plants with vitamin D is ergocalciferol, also known as vitamin D2.

As mentioned above, vitamin D is a pro-hormone. This means that our bodies convert the vitamin into a hormone. In this case, vitamin D becomes converted to the hormone calcitriol so that it can be used by the body.

After vitamin D is either consumed via foods, or absorbed by the skin from the sun, it will eventually reach the bloodstream and liver. In the liver it becomes 25-hydroxyvitamin D, then it will make its way to the kidneys.

In the kidneys, 25-hydroxyvitamin D becomes calcitriol or the fancy name 1, 25 - dihydroxy-vitamin D. This is the hormone made from vitamin D that we as humans use in our body.

So, to make vitamin D into calcitriol we need to get it from the sun or diet, transport it to the liver, than to the kidneys. From there, calcitriol can be distributed around the body.

What does vitamin D do

Aside from specific roles of vitamin D, one of it's main roles is to be the precursor to calcitriol. And calcitriol has many roles in the body.

Here are some of the important roles vitamin D and calcitriol have.

They are involved: calcium regulation, glucose tolerance, gene transcription, cell differentiation, immune function, regulating blood pressure.

And they also increases calcium absorption in the gut, promote bone growth, and are important for muscle and immune function.

Vitamin D has a bigger role in immune function, gene transcription, glucose tolerance, and blood pressure regulation.

While the hormone calcitriol has a bigger role in bone development, calcium regulation, and muscle function.

I don't want to bore you with more than you need know here. So we will move on.

But at the very least, understand that vitamin D and calcitriol both have major roles in our body.

Where can you get vitamin D in your diet

Vitamin D is unique in that the primary source should come from the the rays of the sun. Sure, you can get it within your diet, but compared to the sun, dietary sources of vitamin D are far less.

When the sunlight hits our skin, the cholesterol in our skin cells convert a precursor molecule a pre-vitamin D, and eventually it will get taken up by the blood and head to the liver.

For most people in the world, it is very hard to get the appropriate amount of vitamin D solely from the sun. Current indoor jobs, activities, lifestyle, and environment all play role in this.

This is another reason to incorporate a wide variety of foods to make sure that you can get enough vitamin D.

Food sources of vitamin D, can be found in the following.

  • fatty fish

  • egg yolks

  • shrimp

  • beef liver

  • fish liver

  • mushrooms (the only significant form of vitamin D in plants)

  • Fortified products

For many people, supplementation can be a great way to cover your bases on vitamin D.

However, everyone may need different amounts of vitamin D supplementation. You will really only be able to know for sure after blood work.

But, given the fact that vitamin D is one of the more common vitamin deficiencies, many people can benefit from a vitamin D supplement or multi-vitamin.

Vitamin D is very important to ensure we are function well.

Yes, the sun is the best source of vitamin D, but don't go crazy. Try to shoot for 15 minutes of sunlight each day as best you.

I know this will be hard, it is hard for me too. Some things that may help include walking the dog one extra time during lunch hours, walk and talk on the phone, doing some yard work on the weekends.

I know climate may make this difficult. If this is a situation you are in, be sure that you are consuming a variety of foods, and consider asking your doctor about a vitamin supplement if you are concerned.

Keep following along for more vitamin summaries.

Next up will be vitamin E!



  1. Precision nutrition

  2. Sport Nutrition by Asker Jeukendrup

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