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What's So Special About Vitamin D?

"Some characteristics of vitamin D make it both different than other vitamins, and something you're more likely to be deficient in."

Of all the essential vitamins we need for optimal health, there's one that stands out for a few reasons — vitamin D. On today's Inside Health with Dr. Keller Wortham, MD, we'll learn what makes vitamin D different from other vitamins, what it does for our bodies, where we get it, and what happens if we don't have enough of it. Stay tuned to learn all about this wonderful vitamin.

Video Highlights

  • 01:14: What Makes Vitamin D Unique?
  • 02:36: How the Body Makes Vitamin D
  • 03:47: What Does Vitamin D Do?
  • 06:18: Causes of Vitamin D Deficiency
  • 09:27: What Happens if You’re Deficient in Vitamin D
  • 12:36: How do you know if you have a vitamin D deficiency?  
  • 15:14: Wrap-Up

Dr. Keller recently did a video talking about thetop vitamins that are important to get in your diet. Today we’re going to devote a little more time to one of those — vitamin D. That's because vitamin D is special. Some characteristics of vitamin D make it both different than other vitamins, and something you're more likely to be deficient in. In fact, 1 in 10 people are deficient in vitamin D, and 4 in 10 people don't get enough in their diets.

What Makes Vitamin D Unique?

First of all, vitamin D tends to function less like most vitamins do, and more like certain hormones do. It has both active and inactive forms, and it travels around the body and has an effect on various metabolic functions throughout the body. 

Another reason it’s unique is that we have to get most vitamins from our food sources, from outside of our body. Vitamin D is a little different, in that we can actually make vitamin D within our bodies. However, this process is quite complex and involves multiple organ systems, which why it’s so much more likely that we could get a vitamin D deficiency, compared to other vitamins.  That deficiency can also occur because vitamin D is actually not quite as common in food sources as some of the other vitamins. It’s primarily available in things like eggs,fish,dairy, and some whole grains. So, if adhere to avegan diet or don’t eat a lot of those products, then you could actually be at higher risk for vitamin D deficiency.

How the Body Makes Vitamin D

Remember how we said this is a multi-step process involving multiple organ systems? Here's how it works. Vitamin D begins as cholesterol molecules, which come to the skin and are then changed via UV light exposure and certain enzymes. That leads to the production of the precursors to vitamin D.  From there, that precursor moves to the liver and kidneys, and is further transformed into the next-step form of vitamin D. Then that form has to move to another spot of the kidneys, where it will be activated, to then become the actual activated vitamin D3 that we talk about. So, as you can see, we need skin, UV light, a healthy liver, and healthy kidneys to produce the vitamin D that we need, assuming we are not getting it from our diet.

So those are some things that not only make vitamin D unique, but also set us up for a potential deficiency.  

What Does Vitamin D Do?  

Vitamin D plays very important roles within our body. You might know that the most important role of vitamin D has to do with thebones. Vitamin D is very important for bone health, because it helps get calcium and phosphorus, two important minerals, into the bones.  You can get a ton of calcium and phosphorus in your diet, but if you don't have vitamin D, your bones won't absorb those minerals.

However, it's not just about bone health.  Vitamin D is also very important for ourimmune health, helping us fight against infection. It's also important for our muscle function, to keep our muscles active and healthy, and for our cardiovascular health, to help reduce the risk of heart disease, heart attacks, and strokes. It's important for our respiratory system and brain development, and it can even help in cancer prevention.  

A note about cancer: according to some studies, people who are diagnosed with cancer and take vitamin D see a 13% reduction in risk of dying from that cancer. So, if you are suffering from cancer, please talk to your doctor about taking vitamin D and hopefully reducing the risk of dying. People who take vitamin D regularly have also been shown to have a reduced risk of colon cancer,asthma, type 2diabetes,high blood pressure, Alzheimer’s, and autoimmune diseases. So you certainly want to make sure that you have enough vitamin D in your diet, or that your levels are good, because it can help you prevent a lot of these problems. 

When you go to your doctor, let him or her know if you’re concerned about your vitamin D levels, either because you’re not eating vitamin-rich food sources, or you’re not getting enough sunlight, and tell him you want to be tested.  They can run a vitamin D test and see where your levels are. 

Causes of Vitamin D Deficiency


People might just not be eating enough of the things that have vitamin D in them.  As we already mentioned, vitamin D is available in things like eggs, but it’s mostly in the egg yolk — so, if you're eating egg whites only, you're not getting the benefit. Dairy products are often fortified with vitamin D as well, so you can get it from things like kefir, organic yogurt, or from regular milk.  Fish oils and fish skin also have a lot of vitamin D in them, as do whole grains. So, if you're a vegan, or you avoid grains, or eggs, or dairy, or you just don't frequently eat a lot of that stuff, chances are you're not getting a lot of vitamin D from your food sources.  


We already discussed how we need sunlight to activate our own vitamin D process. If you work inside all the time, or have your skin covered up either because of your work or for religious reasons, or maybe you wear a lot ofsunscreen to protect your skin from the sun — all of those can reduce your exposure to UV light, and therefore your body's ability to start making its own vitamin D. Also, people who have dark skin inherently get less penetration of UV light past the layers of melanin in their skin and therefore less activation of vitamin D.  People who are elderly also find that their skin tends to absorb less UV light, because of changes in the skin, so if you’re a senior you might not be getting enough to activate those first steps to make your precursors to vitamin D.

Kidney Disease

Remember, we talked about the fact that one of the prerequisites of vitamin D production is healthy kidneys. If you havekidney disease, you might not be activating the vitamin D that your body's making.

Digestive Conditions

Problems with the digestive tract can also lead to vitamin D deficiency. If you're trying to absorb vitamin D from your food sources and you have something like Crohn's disease, an inflammatory bowel disease, celiac, or some othergut issue, then you might not be absorbing the vitamin D that you need from your gut, which can put you at risk for a deficiency.


Vitamin D is a fat-soluble vitamin. That means the vitamin is stored in the fat, and when it's stored in the fat, it is not in its accessible active state. If you have a lot of body fat because you'reoverweight or obese then that can pull the vitamin D from your bloodstream and sequester it, so it's not available to do the things that you need it to do.

What Happens if You Are Deficient in Vitamin D

Bone problems 

If you’re deficient in vitamin D, you could develop brittle bones because you're not getting the calcium that vitamin D helps your bones absorb. Children, since they are still developing, can get a disease called Rickets, where the bone formation is completely wrong. This was a much more common disease before some of the foods were fortified with vitamin D. But now that we've got fortified foods, a lot more kids have access to dairy, and eggs, so they’re more likely to get enough vitamin D. If you're older, you could end up with a disease called osteoporosis. This is very common in postmenopausal women, again due to not getting enough calcium into your bones. 

Cardiovascular Risk

Another issue with low vitamin D, iscardiovascular risk. We know that vitamin D is cardioprotective, meaning it helps reduce inflammation in the arteries and keep them healthy. It may even play a role inmanaging cholesterol.  If you are not getting enough vitamin D, you are at an increased risk for heart disease, the number one killer in the U.S. You really want to do whatever you can to reduce your risk of heart disease and that includes making sure you have adequate levels of vitamin D.

Cognitive Impairment

Vitamin D is also really important for brain health. A lot of people today are complaining of experiencing brain fog, and just feeling a little bit off. But not a lot of people know that a vitamin D deficiency can potentially cause some of that cognitive impairment.


Another thing that can happen with vitamin D deficiency, isasthma, especially in kids. So, if your child is experiencing asthma symptoms, one thing you can do is try to make sure their vitamin D has been checked. Talk to your doctor about that.

Some Cancers

We talked about cancers a bit already. Vitamin D deficiency has been associated with several different cancers — colon cancer, blood cancers, and others. So, make sure that your vitamin D levels are normal in order to prevent cancers.

Thyroid Issues

Vitamin D deficiency has also been associated with thyroid issues. Vitamin D is a very important hormone in conversion of T4 to T3 (the active thyroid hormone). If you don't have vitamin D around, you might not be regulating your thyroid the way that you need to be and you could end up with a thyroid deficiency.

How do you know if you have a vitamin D deficiency?  

It’s very easy to get tested for a vitamin D deficiency, so talk to your doctor about that. There are also some symptoms to look out for, although the symptoms can often be rather vague.  

If you have brittle bones, or your bones break easily, or if your child has developed Rickets, you should certainly be screened for vitamin D deficiency, but there are also some other things that can be more subtle: cognitive impairment, confusion, fatigue, and symptoms associated with low thyroid, such as hair falling out, and cold intolerance.  

The fact that these symptoms can be so subtle is why it's really important to make sure your doctor evaluates you for low vitamin D. Also, make sure that you're doing what you can to get enough vitamin D in your diet by eating things like eggs, dairy, and fish, as well as taking a good vitamin D supplement.  

A vitamin D supplement is a great thing to add to your diet, and there are some general recommendations for vitamin D consumption. Vitamin D is measured in International Units (IUs). It’s recommended to take 600 IUs per day until you get up there in age, and then increase it to 800,especially if you're at risk for osteoporosis, in which case up to 4,000 IUs per day is considered safe. 


You might need to do more than that though, especially if you're vitamin D deficient. TheSmarter Vitamin D product has 5,000 IUs in its serving of two soft gels. It is vitamin D3, which is the more advanced active form, and it’s plant-based. Most of the vitamin D we've been discussing has been from animals, but youcan get vitamin D from plants. This is a great way to not only get your vitamin D, but to do it in a vegetarian or vegan way.  It also comes with vitamin K added to it. Vitamin K is super important to help that vitamin D get to where it needs to go. So, you can use it for bone health, and for neurologic health, and to prevent calcium from having a detrimental effect on your body. 


Just to wrap it up, there are a lot of vitamins we need to get from our diets. Vitamin D is a special one, in that wecan get it from our diet but the sources are pretty limited. Although we can make it in our body, it's a very complex process — it needs UV light in the skin, a healthy liver, and healthy kidneys. Often, we're not getting enough sunlight or we're covering ourselves up, or using sunscreen, or maybe we have darker skin, or our kidneys aren't working as well, and all of those can lead to vitamin D deficiencies.  

You learned today that a vitamin D deficiency can increase your risk of various health issues, including: cardiovascular disease, brain disease, cancers, thyroid issues, bone issues, and asthma. So talk to your doctor about whether it makes sense to have you screened for a vitamin D deficiency. If you're deficient, the solution is pretty easy.  Just take a good vitamin D supplement and you'll be back on track.

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