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Vitamin D: Introduction

by Kevin Ahern, PhD
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    00:01 Vitamin D is the other fat-soluble vitamin I want to talk about here.

    00:05 Now, vitamin D is important in a variety of functions in the body.

    00:09 One of the things that we know about for it best is it regulates the intestinal absorption of calcium, iron, magnesium, phosphate, and zinc.

    00:17 We’re going to focus on calcium here.

    00:20 Vitamin D is not exactly a vitamin.

    00:24 Technically, vitamins are something that we can’t make, but we actually make most of the vitamin D that we need.

    00:29 Vitamin D therefore acts more like a hormone then it does like a vitamin, but nonetheless the name persists.

    00:37 Vitamin D is ultimately derived from cholesterol or by supplements that we take.

    00:41 And people who don’t get enough sunlight for example or live in areas where there’s limited sunlight may need supplements to get the full amount of vitamin D that they need for their bodies.

    00:52 Cholecalciferol is a form of vitamin D known as D3, that’s created by exposure to sunlight.

    00:58 And that form of vitamin D3 is also the form that we take when we take oral forms of vitamin D as supplements.

    01:05 The formation of cholecalciferol or vitamin D can happen as a result of reaction that you see in the slide on the right.

    01:14 In this reaction, 7-dehydrocholesterol is converted to cholecalciferol simply by the presence of UV light.

    01:21 So if you get enough UV light and you have a light enough skin, getting sufficient vitamin D isn’t a problem.

    01:27 However, if you don’t get enough exposure to UV light or you’re in an area where you have dark skin and the light levels are low, you may be deficient in the vitamin D.

    01:37 Now, cholecalciferol or vitamin D3 is not the active form of vitamin D.

    01:41 It can be converted into the active form and that is done within the body.

    01:46 You can’t take active vitamin D because if the body gets active vitamin D, it will simply convert it into something else because it’s very important to regulate the proper amount of vitamin D.

    01:57 The body doesn’t want to have too much vitamin D, but too little vitamin D is also a problem.

    02:02 If you have too little vitamin D, you can develop a very serious condition known as rickets.

    02:07 So it’s important to monitor your body’s level of vitamin D.

    02:11 The next time you talk to your doctor, that’s something that you should have checked.

    02:15 Well, vitamin D, as I said is very important for calcium.

    02:18 The body levels of calcium are very delicately balanced in a variety of ways.

    02:25 Vitamin D is involved in the dietary absorption of calcium as you can see here.

    02:30 There’s other factors in the calcium levels in our body that we have to take into consideration.

    02:34 Calcium, of course, is a component of our bones.

    02:38 Calcium is carried within our blood.

    02:40 And calcium is also used within the cells.

    02:43 Calcium is a very important ion for the process known as signalling as we shall see.

    02:50 In this slide, I want to show the chemical reactions that are involved in converting vitamin D3, cholecalciferol, into the active form of vitamin D.

    02:58 This occurs in the liver.

    03:00 The reactions necessary to make this happen are hydroxylations.

    03:03 There’s two different hydroxylations that happens to cholecalciferol.

    03:06 The first hydroxylation creates a compound called calcifediol.

    03:11 And calcifediol has a hydroxyl group placed way out there in that red box as you can see.

    03:16 Calcifediol is also hydroxylated to form calcitriol.

    03:20 And calcitriol puts an extra hydroxyl in the red box that you can see here.

    03:25 This calcitriol that is the active from of vitamin D.

    03:28 And as I said, this is very carefully regulated inside the body.

    03:32 And we’ll see how that regulation happens in just a minute.

    03:36 There are also chemically-modified forms of vitamin D that are sometimes used in supplementation that are also converted into very active forms of vitamin D as we can see.

    03:46 The first of these is known as ergocalciferol or vitamin D2 as it is sometimes called.

    03:51 This is not a natural vitamin.

    03:52 It’s one that is actually manmade but the body recognizes and treats it as if it were in fact a natural vitamin.

    03:59 We can see here that the only difference in structure between ergocalciferol and cholecalciferol are a double bond in the ergocalciferol that you can see in the green box.

    04:08 Ergocalciferol gets hydroxylated in the liver just like cholecalciferol did to create 25-hydroxy ergocalciferol.

    04:16 A second hydroxylation occurs on top of that molecule to give 1,25-ergocalciferol as you can see here.

    04:23 And again, a structure very, very similar to the active natural form of vitamin D.

    04:29 Both 1,25-ergocalciferol and calcitriol act completely in the same way in the body.


    About the Lecture

    The lecture Vitamin D: Introduction by Kevin Ahern, PhD is from the course Vitamins. It contains the following chapters:

    • Vitamin D
    • Vitamin D3 Forms

    Included Quiz Questions

    1. It has its active form carefully regulated in the body.
    2. It is created by exposure of cholesterol to light.
    3. It results in scurvy, if deficient.
    4. All of the answers are true.
    5. None of the answers are true.
    1. It is hydroxylated in the liver to calcifediol.
    2. It is hydroxylated in the liver to calcitriol.
    3. It is a precursor of ergocalciferol.
    4. All of the answers are true.
    5. None of the answers are true.
    1. Ergocalciferol
    2. Cholecalciferol
    3. 7-Dehydrocholesterol
    4. Calcifediol
    5. Calcitriol

    Author of lecture Vitamin D: Introduction

     Kevin Ahern, PhD

    Kevin Ahern, PhD


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