Vitamin D — Transcript

Hi everybody, Dr. Mike here. In this video, I want to take a look at vitamin D. [Music] So remember, vitamin D is one of the four fat-soluble vitamins: D, E, K, and A. A vitamin is a nutrient that we require in very small amounts that we cannot produce ourselves, but we need it for normal growth and development. Vitamin D, being a fat-soluble vitamin, what that means is it can be stored within our body because the cells of our body are surrounded by fatty layers, and it allows for the movement of this vitamin into those cells easily and therefore easy to be stored. Water-soluble vitamins, however, often get excreted from the body quite quickly. That's one of the major differences. So when we look at vitamin D, the first thing you need to be aware of is that the main way that we get vitamin D is through UV exposure or our exposure to sunlight. So this is going to be the first step in the synthesis of a precursor vitamin D to an active vitamin D. We can get some from the food that we eat from animal and plant products, but it's quite minimal, but I'll get there in a second. So our exposure to UV light is going to trigger the conversion of a cholesterol that's present in our skin in our epidermis called 7D hydrocholesterol. What the UV light does is it turns 7D hydrocholesterol into something called cholecalciferol. So cholecalciferol will now be floating around in our bloodstream. Now, when it's floating around in our bloodstream, it's ultimately going to get to our liver, and in our liver, cholecalciferol, which is also known as vitamin D3, still not active yet, it's inactive. Once it gets to the liver, it comes across an enzyme. Now, this enzyme is called 25 hydroxylase, and what it does is it gives a hydrogen to the 25th carbon of this cholecalciferol molecule, this cholesterol molecule, and it turns cholecalciferol into something called 25 hydroxy cholecalciferol, 25 hydroxycholecalciferol, which is also known as calcifediol. Now, interestingly, when we ingest vitamin D, so for example, if we ingest it from animal products, what we usually get it from is fish predominantly and liver. This comes in the form of cholecalciferol or vitamin D3, and therefore it's just going to enter the bloodstream and go via this particular pathway in the liver. If we ingest it through plant products, one of the main ways is UV-activated mushrooms. We actually get ergocalciferol, not cholecalciferol, ergocalciferol, and this is actually vitamin D2, and this will travel to the liver and undergo this hydroxylation through 25 hydroxylase and then go via this calcifediol, which means once this is produced, it then moves to the kidneys. So we've got calcifediol, also known as 25 hydroxycholecalciferol, traveling to the kidneys. It comes across another enzyme in the kidneys, which is called one alpha hydroxylase, and what one alpha hydroxylase does is it gives a hydrogen to the first carbon of this calcifediol. So now we have a molecule which is 1,25 hydroxy cholecalciferol, which is a mouthful, but it's also known as calcitriol. Now, what we have is an active form of vitamin D. Important point: these enzymes here are really important because you're always going to go through this process and turn into calcifediol, this 25 hydroxy cholecalciferol. We're always going to go to this point when you're exposed to sunlight, but that means this enzyme is always going to be activated in the liver. But this enzyme in the kidneys, specifically, it's produced by what's called the proximal convoluted tubule cells. This one alpha hydroxylase needs to be stimulated to be active, right? So what that means is when you get a blood test for vitamin D, you are not actually testing, often you're not testing calcitriol or 1,25 hydroxy cholecalciferol. You're actually testing calcifediol, 25 hydroxy cholecalciferol. That's the one you're actually getting tested for because you're always going to be producing that at all times. So that's a good indicator of your baseline vitamin D, at least precursor. If you've got a problem with calcium, which I'm going to talk about in a sec, then they may test this one down the track. So this gets activated. Now the question is, what activates this? Well, we'll get there in a second because we need to now talk about what does the active form of vitamin D, calcitriol, do. That will tell us here what it needs to do. It needs to increase calcium in the blood. It needs to increase phosphate in the blood. Two really important points. How does it do this? Well, it's stimulated if calcium and phosphate levels are too low, and that means the thing that stimulates one alpha hydroxylase is going to be low calcium, low phosphate. Now think about it like this: what happens is low phosphate, that's going to directly stimulate this enzyme to activate. All right? What indirectly stimulates this is calcium. Low calcium. So when calcium levels are low, it actually travels to the parathyroid gland. So you've got your trachea here, and you've got your thyroid that hugs the front of your trachea. Behind your thyroid, you've got the parathyroid gland. So I'm going to draw the back of your trachea here. So here's the trachea, there's the rings of your trachea. This is at the back. The parathyroid glands are these glands that are embedded in the larger thyroid gland. And what the parathyroid gland does is it produces parathyroid hormone, PTH. So low calcium triggers parathyroid hormone to be released, and parathyroid hormone is going to trigger one alpha hydroxylase. So that means we've now got active vitamin D. Its whole job is to increase calcium because the stimulus was a drop. Increased phosphate, its stimulus was a drop. How does it do it? It does it like this: it increases absorption of both calcium and phosphate at the gastrointestinal tract. It increases reabsorption of calcium and phosphate at the kidneys, so throws it back from the tubes of the kidneys back into the blood. Really important. Increased absorption and also increases osteo activity. Osteo means bone, clast means to crush. It breaks bone down to release calcium and phosphate into the bloodstream. Now you may be thinking, wait a minute, if this is breaking bone down and releasing calcium and phosphate into the bloodstream, don't we need vitamin D for strong bones? This seems like the opposite of what we want. All right, important point: if we have vitamin D, both calcium and phosphate will be released into the bloodstream. Calcium and phosphate love to be together. They're partners for life. They love to be together. When they're together, they precipitate or mineralize into the bone. So you're going to absorb it in the GIT, it's going to be in the blood. You're going to reabsorb it from the kidneys, it's going to be in the blood. Some is going to be taken out of the bone, it's going to be in the blood. It gets together and then goes back into the bone, deposits into the bone, strengthens the bone. That's what we want. Now, important point: if we have no vitamin D and we only have parathyroid hormone, something interesting happens. Calcium increases in the blood, but phosphate gets peed out. That means this connection, this bond of the two, is not present, and bones actually get broken down. So without vitamin D and only parathyroid hormone, bones will start to become brittle. All right, now I want to talk about deficiencies. What happens if we don't have enough? What happens if we have too much? All right, let's have a look. Deficiencies are important. Let me tell you why. Firstly, because 50 percent of the world's population is deficient in vitamin D, and that's because of their lack of exposure to sunlight. The color of your skin actually changes how much vitamin D you produce. If you have lighter skin, you'll produce five times more vitamin D than somebody with darker skin, and this has to do with where the individual is in the world and they're exposed to that sunlight. So let's first talk about deficiencies. So a deficiency, what can cause it? Well, lack of sunlight, obviously, lack of UV light. It can be caused if you've got a problem with fat absorption. Now why? What does this mean? Vitamin D is a fat s...

that we require in very small amounts that we cannot produce ourself but we need it for normal growth and development vitamin d being a fat soluble vitamin what that means is it can be stored within our body because the cells of our body are

surrounded by fatty layers and it allows for the movement of this vitamin into those cells easily and therefore easy to be stored water-soluble vitamins however they often get excreted from the body quite quickly that's one of the major differences so

when we look at vitamin d first thing you need to be aware of is that the main way that we get vitamin d is through uv exposure or our exposure to sunlight so this is going to be the first step

in the synthesis of a precursor vitamin d to an active vitamin d we can get some from the food that we eat from animal and plant products but it's quite minimal but i'll get there in a second so our exposure to uv light

is going to trigger the conversion of a cholesterol that's present in our skin in our epidermis called 7d hydrocholesterol what the uv light does is it turns 7d hydrocholesterol into something called cholecalciferol so colicalciferol will now be floating around in our

bloodstream now when it's floating around in our bloodstream it's ultimately going to get to our liver and in our liver cholecalciferol which is also known as vitamin d3 still not active yet it's inactive once it gets to the liver it comes across

an enzyme now this enzyme is called 25 hydroxylase and what it does is it gives a hydrogen to the 25th carbon of this cholecalciferol molecule this cholesterol molecule and it turns koly kelsey feral into something called 25 hydroxy coli

kelsey ferrell 25 hydroxycholic calcifero which is also known as calcifediol now interestingly when we ingest vitamin d so for example if we ingest it from animal products what we usually get it from is fish predominantly and liver this comes in the form of

cholecalciferol or vitamin d3 and therefore it's just going to enter the bloodstream and go via this particular pathway in the liver if we ingest it through plant products one of the main ways is uv activated mushrooms we actually get ergo calciferol not coli

calciferol ergo calciferol and this is actually vitamin d2 and this will travel to the liver and undergo this hydroxylation through 25 hydroxylase and then go via this calcifedial which means once this is produced it then moves to the kidneys

so we've got calciferdil also known as 25 hydroxycalled calciferol traveling to the kidneys it comes across another enzyme in the kidneys which is called one alpha hydroxylase and what one alpha hydroxylase does is it gives a hydrogen to the first carbon

of this calcifidel so now we have a molecule which is 1 25 hydroxy coli kelsey which is a mouthful but it's also known as calcitriol now what we have is an active form of vitamin d important point these enzymes here

really important because you're always going to go through this process and turn into calcifedeal this 25 hydroxy coli calciferol we're always going to go to this point when you're exposed to sunlight but that means this enzyme is always going

to be activated in the liver but this enzyme in the kidneys specifically it's produced by what's called the proximal convoluted tubule cells this one alpha hydroxylase that needs to be stimulated to be active right so what that means is when you get a

blood test for vitamin d you are not actually testing often you're not testing kelsey triol or 125 hydroxy color kelsey ferrell you're actually calcified 25 hydroxycoli calciferol that's the one you're actually getting tested for because you're always going to be

producing that at all times so that's a good indicator of your baseline vitamin d at least precursor if you've got a problem with calcium which i'm going to talk about in a sec then they may test this one down the track so this gets

activated now the question is what activates this well we'll get there in a second because we need to now talk about what does the active form of vitamin d calcitriol do that will tell us here what it needs to

do is it needs to increase calcium in the blood it needs to increase phosphate in the blood two really important points how does it do this well it's stimulated if calcium and phosphate levels are too low and that means

the thing that stimulates one alpha hydroxylase is going to be low calcium low phosphate now think about like this what happens is low phosphate that's going to directly stimulate this enzyme to activate all right what indirectly stimulates this

is calcium low calcium so when calcium levels are low it actually travels to the parathyroid gland so you've got your trick here and you've got your thyroid that hugs the front of your trachea behind your thyroid you've got the

parathyroid gland so i'm going to draw the back of your trick here so here's the trachea there's the rings of your tricky this is at the back the parathyroid glands are these glands that are embedded in the larger thyroid gland and what the

parathyroid gland does is it produces parathyroid hormone p t h so low calcium triggered parathyroid hormone to be released and parathyroid hormone is going to trigger one alpha hydroxylase so that means we've now got active vitamin d it's whole job is to increase calcium

because the stimulus was a drop increased phosphate its stimulus was a drop how does it do it it does it like this it increases absorption of both calcium and phosphate at the gastrointestinal tract it increases reabsorption of calcium and phosphate at the kidneys

so throws it back from the tubes of the kidneys back into the blood really important increased absorption and also increases osteo activity osteo means bone clast means to crush it breaks bone down to release calcium and phosphate into the bloodstream now you may be

thinking wait a minute if this is breaking bone down and releasing calcium and phosphate into the bloodstream don't we need vitamin d for strong bones this seems like the opposite of what we want all right important point if we have vitamin d both

calcium and phosphate will be released into the bloodstream calcium and phosphate love to be together they're partners for life they love to be together when they're together they precipitate or mineralize into the bone so you're going to absorb

it in the git it's going to be in the blood you're going to reabsorb it from the kidneys it's going to be in the blood some is going to be taken out of the bone it's going to be in the blood it

gets together and then goes back into the bone deposits into the bone strengthens the bone that's what we want now important point if we have no vitamin d and we only have parathyroid hormone something interesting happens calcium increases in the blood

but phosphate gets peed out that means this connection this bond of the two is not present and bones actually get broken down so without vitamin d and only parathyroid hormone bones will start to become brittle all right now i want to talk about deficiencies

what happens if we don't have enough what happens if we have too much all right let's have a look deficiencies are important let me tell you why firstly because 50 percent of the world's population is deficient in vitamin d and that's

because of their lack of exposure to sunlight the color of your skin actually changes how much vitamin d you produce if you have lighter skin you'll produce five times more vitamin d than somebody with darker skin and this

has to do with where the individual is in the world and they're exposed to that sunlight so let's first talk about deficiencies so a deficiency what can cause it well lack of sunlight obviously lack of uv light it can be caused if you've got a problem

with fat absorption now why what does this mean vitamin d is a fat soluble vitamin it needs fat in order to be absorbed from the intestines into the lymphatic system then to go from the lymphatic system into the bloodstream and into the

tissues of the body if you've got a problem with fat absorption so what could that be an issue with your bile for example or maybe it's a problem with your intestinal tract doesn't allow you to absorb fats this can have a problem and lead to

diminished vitamin d and maybe you're not getting enough vitamin d from the diet now the main issue here with the deficiency is going to be the exposure to uv light so the question then is how much vitamin d should we be having

so somebody under one year of age around about 400 international units 600 international units if you're between 1 to 70 years and 800 international units if you're above 70 years of age so what happens if you don't have enough vitamin d

well you can have something called rickets if you're a child or you can have something called osteomalacia if you're an adult it's basically the same thing right both are vitamin d deficiencies that result in issues with bone now here's the thing if it happens

in a child their bone has not matured yet so there's a lot of collagen and not a lot of the hard stuff the solidified mineralized bone tissue from the calcium of phosphate so if somebody doesn't have enough vitamin d and the calcium of phosphate

is leaving it's still collagenous so it's bendy so somebody with rickets gets bendy bones because they're a child and the bone hasn't matured somebody with osteomalacia this is an adult so ricketts happens in children osteomalacia as an adult the bone has

mineralized and has hardened so what's now happening is you're pulling calcium and phosphate out of already hardened bones so it doesn't become bendy it just becomes brittle and this is what happens in osteomalacia brittle bones all right so the best way

to get vitamin d especially if one of these disorders is through supplementation obviously uv exposure but supplementation as well now what this also means is anytime you're exposed or start to ingest supplements you have the risk of overdosing

overdosing vitamin d very bad very toxic it's one of the worst types of toxicities you can get from having too much vitamins so let's have a look at what happens when you have too much vitamin d so overexposure now you're not going to

get overexposure vitamin d from sunlight you will get overexposure vitamin d from supplementation so what happens is this you get stones bones abdominal moans and psychic groans this is an old-school way of remembering what happens if you have too much

vitamin d stones bones abdominal moans and psychic growns let's have a look so stones increase the amount of calcium increases the likelihood of calcium-based kidney stones they're the stones bones we spoke about osteomalacia right if you're an adult which i assume this

is going to be abdominal hormones calcium remember you're going to have too much calcium floating through the bloodstream this is the problem with an over amount of overabundance of vitamin d abdominal moans calcium we need to tell muscle to contract

so it contracts the smooth muscle of the abdomen contracts the smooth muscle and anytime you have abdominal pain it's because the muscle is contracting over something so contraction and psychic groans now what's this referring to too much calcium blocks your neurons

ability to fire properly so you get a depression of the nervous system now not depression in the classical sense but just a depression in the firing of the nervous system so nervous depression leading to the psychic groans so

what we've had a look at here is vitamin d how it's synthesized what happens if you don't have enough or if you have too much