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
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:
- Fish liver oil
- Egg yolk
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-hydroxyla