Unpacking Vitamin D Production, Storage, and Transport

There is perhaps no vitamin more famous than vitamin D. Everyone knows that this “sunshine” vitamin is important and recognizes that it has something to do with strong bones. But many people don’t understand the fascinating process that occurs in your body when it is exposed to sunlight and just how critical this vitamin is for protecting your health and well-being. 

Let’s dig into the science behind vitamin D production, storage, and transport to grasp the scope of this all-star vitamin.

What is a vitamin?

Vitamins are essential molecules that your body cannot make by itself but that you need for normal growth and development. Most vitamins come from dietary sources such as food or supplements. Vitamins D is unique, however. 

It is technically a hormone, not a vitamin, as it doesn’t have to come from dietary sources. While you can get it from diet and supplementation, the best source is sunlight. Your incredible body uses UVB rays to produce vitamin D. But how does that process work exactly?

Before we get into the process, let’s define what vitamin D is. 

Vitamin D is fat-soluble

Vitamin D is a fat-soluble vitamin that can be stored in your cells. Unlike water-soluble vitamins (B, C), which are excreted by the kidneys fairly quickly, fat-soluble vitamins (A, E, K, D) stick around for a while. 

Fat-soluble vitamins do not dissolve in water, and your body absorbs them similarly to dietary fats. This creates a reserve that your body can access when needed. 

Vitamin D is stored in the liver, making deficiency less likely than water-soluble vitamins. 

We are in a vitamin D deficiency crisis

With the advent of sunscreen, indoor jobs, and sun avoidance recommended by dermatology and cancer associations, we are facing a global vitamin D crisis.

 It is estimated that almost 50 percent of the population has a vitamin D insufficiency, meaning they aren’t getting adequate amounts through sunshine, supplementation, or diet. 

How do you get vitamin D?

Your body synthesizes it when your bare skin is exposed to sunlight.

You can also get vitamin D from:

  • Supplements
  • Fish liver oil
  • Liver
  • Egg yolk
  • Butter
  • Lard
  • Cod
  • Tuna
  • Salmon
  • Mushrooms
  • Mackerel
  • Sardines
  • Anchovies

How the body produce vitamin D?

The human body is a masterpiece. The process that occurs behind the scenes when you go for a walk on a sunny day is incredible and is a testament to your hard-working organs. Here’s what happens when that warm sunlight hits your skin. 

Step 1: Sunlight, skin, and 7-dehydrocholesterol

In your skin, specifically your epidermis (the top layer of your skin), you have a form of cholesterol known as 7-dehydrocholesterol, the precursor in vitamin D synthesis. When skin is exposed to UVB light,  7-dehydrocholesterol journeys through your organs, ultimately becoming the active form of vitamin D. 

Step 2: D3 in the bloodstream

Once the sun shines on the 7-dehydrocholesterol in your skin, it becomes cholecalciferol or vitamin D3. The D3 is now floating around in your bloodstream but is still not an active form of vitamin D. 

Note: When we ingest vitamin D from animal products, it comes in the form of cholecalciferol (D3) and will go straight to the bloodstream to continue the activation process through your organs.

Step 3: The liver

Next, D3 travels to the liver, where it encounters an enzyme called 25-hydroxylase. This enzyme gives a hydrogen molecule to the 25th carbon of the cholecalciferol molecule, a process known as hydroxylation. A new name is given to our advancing cholesterol, 25-hydroxycholecalciferol or calcifediol.

Note: When we ingest mushrooms (the only plant-based source of vitamin D in nature), we get ergocalciferol (D2). Instead of going into the bloodstream, like D3 from animal sources, it goes to the liver, where it undergoes hydroxylation and continues into the kidneys as calcifediol. 

Most researchers agree that D2 is not at potent as D3. Therefore, if you want to purchase a supplement, always buy vitamin D3. 

Remember, vitamin D can be stored for a time in your fat and liver, which could help keep your levels up during the winter months when the sun is weak in certain locations

Step 4: Kidneys and activation 

25-hydroxycholecalciferol (a mouthful, we know) goes to the kidneys for the final conversion step. Here, it comes across the enzyme 1alpha-hydroxylase. 1alpha-hydroxylase gives a hydrogen molecule to the first carbon of the calcifediol. 

This entire journey through the organs ends with 1. 25 hydroxycholecalciferol or calcitriol, the active form of vitamin D in the kidneys.  

The final enzyme in the vitamin D process, 1alpha-hydroxylase, needs to be stimulated to activate the vitamin D. 

Step 5: Phosphate and calcium

The active form of vitamin D, calcitriol, is essential for bone health, but how does it impact your bones, and what is the relationship between vitamin D and calcium?

Calcitriol increases calcium and phosphate in the blood when calcium and phosphate levels are too low. So how does it know when to increase calcium and phosphate?

Remember that the final enzyme needs to be activated to convert vitamin D into its active form? Low phosphate directly stimulates this enzyme, while calcium indirectly stimulates it through the thyroid. 

The parathyroid gland (behind the trachea) is notified when calcium levels are low. The parathyroid gland produces parathyroid hormone (PTH), which triggers 1alpha-hydroxylase. 

When calcium and phosphate levels are low, the 1alpha-hydroxylase enzyme goes into action, taking that calcifediol (that it got from the liver) and converting it into calcitriol, which can raise those calcium and phosphate levels.

How does calcitriol improve calcium and phosphate levels?

What does calcitriol do?

Vitamin D is now activated and ready to come to the rescue to increase calcium and phosphate levels. It does this by:

  • Increasing absorption of calcium and phosphate in the gastrointestinal tract (GIT). 
  • Increasing reabsorption of calcium and phosphate from the kidneys to the bloodstream. 
  • Breaking bones down to release the calcium and phosphate from those bones back into the bloodstream.

Wait, that can’t be right, can it? Isn’t the whole point of vitamin D to support healthy bones? Why would we want it to break bones down? 

Though it may seem counterintuitive, this process ultimately strengthens the bones. Calcium and phosphate love to be together, and when they are released back into the bloodstream, they will mineralize into the bone from the blood. 

Through these three ways, vitamin D returns calcium and phosphate to the blood, going right into the bone and strengthening it. 

Vitamin D receptors

Throughout your body, you have vitamin D receptors. These are proteins that bind to vitamin D and work to keep your organs happy and well-functioning. They are responsible for capturing vitamin D in the intestines and enabling calcium absorption.

Vitamin D can also help prevent cancer cell multiplication and cause the death of cancer cells. Specifically, it has been studied and shown to be possibly effective in reducing prostate cancer, as the prostate has many vitamin D receptors. 

What if you don’t have enough vitamin D?

Vitamin D deficiency 

What causes vitamin D deficiency?

  • Lack of exposure to sunlight — risk increases based on location, skin tone, and sunscreen use. This is the primary cause of deficiency. 
  • Poor diet
  • Problems with the gastrointestinal tract (GIT)
  • Fat-absorption issues
  • Certain kidney and liver disorders

Symptoms of vitamin D deficiency

If you have no vitamin D and only parathyroid hormone (triggered by low calcium), calcium increases in the blood, but phosphate is simply peed out. Meaning, the essential connection between phosphate and calcium is not present, and calcium is not absorbed correctly. Without vitamin D, the bones start to break down.

This can lead to:

Vitamin D deficiency has also been linked to:

What if you have too much vitamin D?

Because your body stores vitamin D, it is possible to have a toxic amount from supplementation. This is primarily due to excessive calcium in the bloodstream and intestines.

Most people don’t need to worry about having too much vitamin D. It is impossible to get too much from the sun. Your body will stop producing vitamin D when you get sufficient levels. However, mega doses of supplements over long periods can lead to dangerous vitamin D levels and a variety of health complications, including:

  • Kidney stones (from too much calcium)
  • Confusion 
  • Nausea or vomiting
  • Muscle weakness
  • Headache
  • Abdominal pain 
  • Heart arrhythmias

Sunshine is important: There is no “D”ebate

While food and quality supplements (such as our Super D) can help support your vitamin D levels in the winter, the sun is the single best source of this crucial vitamin. Now that you know what your body goes through to produce vitamin D, you’ll likely be more motivated to spend time basking in the sun’s glow. Get outside. Get sunshine. Achieve your 100 Year Heart.

Eat Well · Live Well · Think Well 


Medical Review 2022: Dr. Lauren Lattanza NMD

In order to live well, one must eat well.

Get the Natural Heart Doctor approved Diet and discover how to eat for your 100 Year Heart.

Work With Us

Discover how we can help you achieve your 100 Year Heart.

NHD Patient Application Form

SUBSCRIBE TO THE NATURAL HEART DOCTOR NEWSLETTER

Join our community by subscribing to the free, Natural Heart Doctor Newsletter. You'll receive great natural health news delivered right to your inbox.
Join 30,000+ subscribers.
It’s completely free.