March 28, 2023

Vitamin D Deficiency | Absorption & Metabolism, Purpose of Vitamin D, Causes of Deficiency

Hey everyone this is an introductory lesson on vitamin d deficiency so we’re going to talk about what vitamin d is we’re also going to talk about some of the sources of vitamin d we’re also going to talk about how it’s absorbed and metabolized why we need vitamin d what it actually does in our body and at the end of this lesson we’re going to talk about a variety

Of causes of vitamin d deficiency so vitamin d deficiency is actually very common around the world it is a global phenomenon and vitamin d itself is a fat soluble vitamin there are multiple forms of vitamin d we’re going to talk about in this lesson one of them is vitamin d2 also known as ergocalciferol and there’s also vitamin d3 which is caulicalciferol and

Because vitamin d is a fat soluble vitamin it is mainly stored in fat tissue so vitamin d is required for several processes we’re going to talk about these processes in more detail later but i’m just going to briefly introduce the processes here one is calcium homeostasis so it’s important in calcium homeostasis it’s also important in bone maintenance and

Metabolism and it’s also important in immune system functioning what are the sources of vitamin d where do we actually get vitamin d so we can get vitamin d from our diets so animal food products like fish and meat do contain some vitamin d fortified dairy milk so dairy milk that’s literally had vitamin d added to it also is a source of vitamin d and vitamin

D supplements so taking an over-the-counter vitamin d pill is another source as well but we can also get vitamin d through endogenous synthesis so endogenous synthesis means that we’re synthesizing vitamin d in our own body and that’s actually derived from cholesterol in our skin when it is exposed to sunlight so vitamin d can be derived from this process when

Our skin is exposed sunlight and it’s actually vitamin d3 that is produced so caulicalciferol and the recommended daily intake of vitamin d differs depending on the age of the patient so i won’t go over all the numbers for each age group here if you want more information please check out the reference in the description below and as we’ll see later different

Populations require different amounts than the ones stated here so how is vitamin d absorbed and metabolized so when you actually do ingest it or if it’s synthesized in your skin when your skin’s exposed to sunlight what happens so i’m going to first briefly talk about vitamin d absorption when we actually ingest it from our diet so if we actually eat vitamin d

From our diet it goes into the gastrointestinal system and because it’s a fat soluble vitamin we need bile bile helps to emulsify fats and we also need certain pancreatic enzymes like lipase to break down those fats so we can get access to that vitamin d and eventually as it traverses through the gastrointestinal system it gets absorbed in the ileum and the other

Mechanism by which we get vitamin d is through endogenous synthesis i’m not going to go through the mechanism here that’s a topic for another lesson so nonetheless when the skin is exposed to sunlight it produces vitamin d3 cholecalciferol we can get vitamin d2 and vitamin d3 from our diet but from the skin the endogenous synthesis it is vitamin d3 now when we do

Have vitamin d2 and vitamin d3 they both go to the liver and they get acted on by an enzyme in the liver 25 hydroxylase enzyme and it adds a oh group and hydroxyl group to each of them so we get 25 hydroxyl vitamin d2 so we can see here this hydroxyl group has been added and we also get 25 hydroxy vitamin d3 and we can see that the hydroxyl group has been added

Here as well and the next destination is the kidneys and in the kidneys there’s another enzyme one alpha hydroxylase and one alpha hydroxylase enzyme adds another hydroxyl group and the addition of the hydrox group is actually on the opposite end so we’ve added one hydroxyl group here and another one here so now we’ve got 125 hydroxy vitamin d and this is also

Known as calcitriol try all three all so three hydroxyl groups we’ve added two and we actually started with one so we’ve actually got three hydroxyl groups now so calcitriol three hydroxyl groups and it’s also known as 125 hydroxy vitamin d so what does vitamin d do why do we actually need vitamin d so vitamin d when i’m talking about vitamin d here i’m actually

Talking about calcitriol so it’s the active form of vitamin d as you can see there’s three hydroxyl groups here calcitriol as you mentioned before is important in calcium homeostasis and bone maintenance so why is that so when we actually have calcitriol this active form of vitamin d it helps us absorb calcium and phosphate from our gastrointestinal system it

Also helps us reabsorb calcium and phosphate from our renal system from our kidneys so those are two main mechanisms as to bringing in calcium and phosphate and how does it do this in the gastrointestinal system so i’ve got a pathway here if you want more information i have an entire lesson on this pathway vitamin d and calcium but briefly in an interest site so

Here is a cell of the intestinal epithelium and here’s the intestinal lumen here’s the blood vessel calcitriol enters into the entro site and it can do a couple of different things it can enter into the nucleus and activate genetic programs that lead to the production of calcium transporters on the intestinal lumen side it can increase expression of calbinin

And it can increase expression of atp dependent calcium pump on the opposite end of the intra site so all of this leads to more calcium being brought into the enterocyte and more calcium being pumped into the blood vessel so it helps absorb calcium we need calcium for bone development and maintenance so our bones are made of calcium and phosphate so we need

Both calcium and phosphate so vitamin d is extremely important in having enough calcium for our bones and another thing that vitamin d does is immune system regulation so i have an entire lesson on this as well vitamin d and immune system function with regards to sars cov2 if you want more information please check out that lesson i’ll briefly talk about it

Here so vitamin d is involved in immune system regulation by way of inducing expression of antimicrobial peptides so peptides that go against microbes these include catholicitans so it helps produce catholicism antimicrobial peptide or camp camp and another category of antimicrobial peptides defensins these are expressed in leukocytes and epithelial cells and

There’s alpha and beta defensins so vitamin d can induce catholicisms like camp and this antimicrobial peptide can bind to bacteria and reduce bacterial functioning and then with the fensons the fencing production can be induced by vitamin d and these defenses can actually bind to viruses like influenza virus and that actually prevents and reduces the influenza

Viruses ability to bind and infect other cells and these defenses have also been shown to bind to bacterial membranes as well so again vitamin d is important in calcium homeostasis and bone development and maintenance and immune system regulation through its ability to induce antimicrobial peptides so what are some of the causes of vitamin d deficiency one of

Them is actually reduced exposure to sunlight so we can see this in people that have a generally reduced sun exposure so if they’re inside a lot or they’re institutionalized they’re not able to get sun exposure we can see vitamin d deficiency in these individuals dark skinned individuals are at an increased risk as well and older individuals so as individuals

Get older they also have a reduced ability to absorb vitamin d another category of causes is decreased endogenous synthesis so really the decreased endogenous synthesis really has to do with the modification of the vitamin d after it has been absorbed so we talked about the liver and the kidneys being important areas where vitamin d is modified and formed into

Its active mature form calcitriol so in some cirrhosis patients they won’t be able to add that hydroxyl group to form 25 hydroxy vitamin d in renal failure they may be lacking one alpha hydroxylase enzyme so they won’t be able to completely form calcitriol another category is reduced dietary intake generally speaking we see this mostly in the elderly population

Another category is malabsorption so in patients who have a malabsorptive process like celiac disease and crohn’s disease chronic pancreatic insufficiency in cystic fibrosis we can also see issues with absorbing vitamin d so with regards to crohn’s disease often times the terminal ileum is affected that is the place where we absorb fat soluble vitamins chronic

Pancreatic insufficiency is a cause because they’re not able to produce pancreatic enzymes like lipase in order to break down fats and get access to that vitamin d and cystic fibrosis for a similar reason the other category is medications so medications like spironolactone rifampin clotrimozole dexamethasone phenobarbital and carbamazepine also can lead to a

Vitamin d deficiency as well these actually decrease activity of enzymes in the liver so decreasing activity of 25 hydroxylase enzyme for instance and another category of causes is genetic causes so there’s a genetic condition of hereditary vitamin d resistance and we call this hereditary vitamin d resistant rickets so even though they have vitamin d they’ve

Absorbed it there’s nothing wrong with the production of vitamin d it’s not being able to be used properly and out of all these categories the individuals at the highest risk of vitamin d deficiency are elderly patients overweight and obese patients and institutionalized patients so i hope you found this lesson helpful and informative if you did please give it

A thumbs up and consider liking subscribing and clicking the notification bell to help support the channel and stay up to date on future lessons in the next lesson we’re going to talk about the signs and symptoms ways to diagnose it and ways to treat vitamin d deficiency so check out that lesson for more information thanks so much for watching and i hope to see you next time

Transcribed from video
Vitamin D Deficiency | Absorption & Metabolism, Purpose of Vit D, Causes of Deficiency By JJ Medicine