Why is vitamin D so important to your body? Maybe you’ve heard it helps with your bone health, your immune system, and even calcium getting involved. And yes, we’ll definitely talk about the sun and your skin getting involved in this story about vitamin D. But did you know that your liver and kidneys play a huge role in vitamin D synthesis? So we’ll take a look at those organs as well as answer some questions like why are many people deficient with this vitamin?

And how do you get adequate amounts inside of your body? It’s going to be a fun one. So let’s do this.

Can Vitamin Really Be Made In The Skin?

Now, one of the characteristics of vitamin D is that it’s a fat-soluble vitamin. Fat-soluble vitamins dissolve in fats and tend to accumulate more in the body as compared to, say, water-soluble vitamins, like vitamin C. Now, there are many compounds that belong to the vitamin D family and they all have similar functions, but by far the most important is vitamin D3, also known as colacalcipherel.

Now, this can be synthesized in the skin, but we need UV light to do it. So let’s use this example. Down here on this skin dissection we have, where I’m tracing with the probe, is the top layer of the skin called the epidermis. And this cut edge there, the majority of that is actually the second layer down called the dermis. But in the epidermis, we’re going to see this other compound called seven dehydro cholesterol.

And when the UV light comes down and hits the epidermis, that seven dehydro cholesterol within the epidermis gets converted to vitamin D3. And so, in theory, we could get all the vitamin D3 that we needed from UV exposure. We can also get it from our daily foods.

Granted, there’s not a ton of foods that are just packed with vitamin D, but you find it in like, fatty fish or fish oils and also in some of our fortified products like we’ve fortified a lot of dairy products like milk, and even fortified things like orange juice. And you can even get it through supplementation.

Why Are Some People Vitamin D Deficient?

But what’s crazy to think about is that there are still many people who are deficient in vitamin D3 or colicalciphers. And when you think about it from this perspective, say you live in the northern hemisphere and you’re one of those people that is exposed to those gnarly winters where the days get shorter and you’re inside more and you don’t get a ton of sun exposure.

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There are many situations with people where cutaneous synthesis or synthesis of vitamin D in the skin ceases in the winter. And so in that case, you’d have to get it through the diet or supplementation. Now, another thing that I think is really interesting is if the skin pigment is darker, or I should say the darker the skin pigment, the longer it takes or the more sun exposure is needed to have that conversion process take place.

And so we’re also seeing risk factors in people who are elderly if they’re staying inside more. You also don’t convert things as efficiently when you’re getting older in life. I know it’s a shame, but one of the things to think about is, how do I know if I’m deficient? Because you don’t really get symptoms until you get really severely deficient. People with mild to moderate deficiency won’t even know it.

And the answer to that, to knowing this, is you’ve pretty much got to get tested.

Why Vitamin D Is “Worthless” Without The Liver!

So we’ve got this vitamin D3 or cola calciferol that was either synthesized in the skin or ingested through our diet, food, or supplementation. But this is still not considered the activated form of vitamin D3. We need to actually have it go through a couple of conversion processes. And that vitamin D3 whether it was ingested or synthesized in the skin, it’s going to be circulating throughout the blood and it will eventually pass through this amazing organ here called the liver.

And I’m tracing the bottom portions of the liver here, and I’m just reflecting this muscle called the diaphragm that’s draped over the liver. But once that vitamin D Three, again, known as cholecalciferol, makes it into the liver, it will start converting it into something called 25 deoxycholic calciferol. And this is a really cool thing, too, that happens. The liver has a feedback mechanism.

As the levels of that conversion go up, as it’s making more 25 hydroxy cholecalciferol, eventually it’s going to shut off the conversion, even if there’s more vitamin D3. And this is a really cool way that the liver regulates the blood levels of that new 25 deoxycholic calciferol and the excess vitamin D that wasn’t converted can get stored in the liver.

So that kind of creates this mechanism that if you ingest a high amount of vitamin D, you can store the extra in that liver. And so now you might be thinking, okay, we’ve converted. It totally active, right?

No, we still have one other place and another conversion step that has to happen.

Why Vitamin D Is “Worthless” Without The Kidneys And PTH!

So now this 25 deoxycholic calciferol that was converted in the liver from vitamin D three is going to go through the bloodstream again and eventually make it to another set of organs called the kidneys. If you take a look at this cold section here, we’ve got this frontal section through this kidney. And that 25 hydroxy cholecalciferol is going to go through the bloodstream here. And eventually, you can see those blood vessels branching, and they will eventually make it out to the outer portion of the kidney, referred to as the renal cortex.

And within that renal cortex, there are these tiny little tubules called Roxana convoluted tubules. And inside those tubules, under the direction of this hormone called parathyroid hormone, the kidney will complete the final conversion into something called 125 dihydroxycholocalcipherol.

The name just keeps getting longer, but we’re finally to this fully active form of vitamin D, so it can start to have its main effects. But I do want to go back to that parathyroid hormone that I mentioned. If I go to this other dissection here, this is a trachea or your windpipe.

And here is your larynx, which we nickname your Adam’s apple. So me touching right there is the same as me touching here. But I want to reference below the larynx or Adam’s apple, this structure or little organ called the thyroid gland. And within the thyroid gland, you can’t really see them, but they’re embedded in here are the parathyroid glands. The parathyroid glands, surprise, surprise, secrete parathyroid hormone.

And parathyroid hormone is all about regulating calcium levels in the blood. So in a way, we can kind of think of this parathyroid hormone as telling the kidney, hey, we need the final conversion of this vitamin D three to its activated version so we can get more calcium into the bloodstream.

The Main Reason For Vitamin D – Calcium

Now, you may have heard of this link before between vitamin D three and calcium. And here’s exactly what’s going on here. It’s super cool that now converted 125 dihydroxy cholecalciferol, you know, it’s kind of fun to say, will have an effect on the digestive tract, specifically the small intestine.

But let me reflect on this fatty apron called the greater momentum. And then you can see the small intestine in the abdominal cavity here. Now, again, the small intestine is a hollow tube where food is going to pass through and be absorbed. But again, keep in mind, that this is a hollow tube. And the inside lining of that tube has the cells that are going to be absorbing nutrients.

And in this case, we’re going to be talking calcium. That 125 dihydroxy cola calciferol causes these intestinal cells to make more calcium-binding proteins. So it’ll bind the calcium and bring it into the body. From the things that you’ve ingested, it’s super amazing. And calcium is so important to body functions.

Bone health is so important with calcium. Also, for proper functioning, nervous tissue, and muscle tissue, calcium is important. So you can see why this vitamin D three going through this activation process so it can absorb this. Calcium is so important and frankly, quite amazing.

Putting This All Together

And because it is so amazing, I want to take the chance to do a whiteboard session to make sure we’re clear on all the steps we just talked about.

So we’ve got this area, this box, representing our skin. And inside our skin, we have 70 hydrocholesterol. And as the beautiful rays of the sun shine upon our skin, that 70 hydrocholesterol gets converted into vitamin D three. Now, this is one pathway. We can also ingest vitamin D Three through our diet, put it in our mouth, swallow it down, and poof.

Both of these pathways will end up in the same place by going to the liver. But vitamin D Three, once it’s in the liver, will get converted into the 25 hydroxychola calciferol. Now, I did mention there’s this cool feedback mechanism with the liver that as the levels of 25 hydroxycholicalcipherol increase, eventually, the liver is going to be like, okay, let’s shut this conversion process from here to here down, because we’ve got enough of this.

And any of the extra vitamin D three, say we’re getting lots of sun exposure, or we’re ingesting a lot in our diet, any of that extra vitamin D three can be stored in the liver for later conversion to start this process again when needed. Now, once this is converted, it will eventually make it down into the kidneys and under the direction of the parathyroid gland, it secretes the parathyroid hormone, because, again, the parathyroid gland is all about regulating calcium levels in the bloodstream.

We’ll get this conversion of 25 deoxycholic calciphrol into the 125 dihydroxycholocalcipherol. Again, totally fun to say.

And the reason there are cute little stars here is that this is when we’ve got kind of our activated form here. This is where we’re going to have some of the magic happen because this will then move into the small intestine, and that 125 dihydroxycholic calciferol will increase the number of calcium-binding proteins in the cells of the intestine, those cells that absorb nutrients. And if we increase those proteins, we increase the amount of calcium absorption. And that’s one of the main functions of vitamin D. It’s all about getting more calcium into the bloodstream. And like we said earlier, it’s pretty amazing.

What Else Can Vitamin D Do?

And if the effects of vitamin D on calcium aren’t amazing enough, there are some other potential effects that vitamin D can have throughout your body. I say potential because there’s a need for more research and more information about how these mechanisms work through vitamin D.

For example, many of your immune cells have the receptor for the activated form of vitamin D. So it’s thought that it may promote your immune system, and help with infections as well as inflammation. There are also some laboratory studies that show that vitamin D may also inhibit the growth of cancer cells.

What Are The Symptoms Of Vitamin D Deficiency?

And let me just come back to this discussion about vitamin D deficiency. As we mentioned earlier, people with mild to moderate deficiencies often don’t know because they’re asymptomatic. Again, the only way to know in that situation is through proper testing.

But as the deficiency becomes more prolonged or more severe, then things can start to manifest as symptoms. They most often manifest with the bones. Because remember, when we don’t have vitamin D, we’re not going to be able to absorb calcium into the bloodstream.

What happens is it gets pulled from the storage in the bone and then bones can become weaker. You can get bone pain, and even easier fractures, and sometimes people can develop something called osteomalacia, which is the softening of bone tissue.

Rickets is a kid’s version of osteomalacia. And luckily, because of our knowledge of this and our ability to supplement, we don’t see that as much anymore. But again, kind of this cool thing to think about with vitamin D.

Does Sunscreen Block Vitamin D Production?

And I can get it from the sun if I want to. And I just have to mention one thing about that, because I’m one of those people who burns pretty easily.

And so I layer up with sunscreen, which will inhibit vitamin D formation because that sunscreen blocks out UV rays. And so it’s kind of a mean trick. I feel like it’s like this Catch-22 where you’re supposed to get some sun exposure, but if you get too much, you’re at risk of skin cancer if you have lighter skin. But luckily, we’ve got those supplements.