Nov. 28, 2020

"Vitamin D and the Athlete" with Dr Daniel Owens PhD

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Episode 149 of the Institute of Performance Nutrition's "We Do Science" podcast! In this episode, I (Laurent Bannock) discuss "Vitamin D and the Athlete" with Dr Daniel Owens PhD (Liverpool John Moores University, UK).

Discussion Topics Include:

  • Overview of Vitamin D and its unique characteristics
  • Why Vitamin D is one of the most "on trend" sports supplements used by elite and recreational athletes
  • From health to performance: The biological influences of Vitamin D (incl. immunity, bone, and muscle)
  • Deficiency, insufficiency and adequacy explored (incl. influencing factors such as diet, sun exposure during winter, skin colour, clothing and sunscreen etc)
  • Test, don't guess: assessing Vitamin D Status
  • Vitamin D supplements (incl. dosage, what forms, when, and when not to supplement))

Podcast Episode Transcript:Download PDF Copy

Key Paper(s) Discussed / Referred to:

Related Podcast Episodes:

Check out our other podcasts, publications, events, and professional education programs for current and aspiring sports nutritionists at and follow our social media outputs via @TheIOPN



We Do Science Podcast


NOV. 28, 2020

"Vitamin D and the Athlete" withDr Daniel OwensPhD




[00:00:00] LB: Hi and welcome back to the Institute of Performance NutritionWe Do Science” podcast, the IOPNpodcast with me, Dr. Laurent Bannock as the host for this podcast. So welcome back. I cannot wait for you to listen to today's episode that I have just recorded. Just giving you a little overview and introduction before you get to enjoy our conversation, or my conversation with my guest today, which was Dr. Dan, or Daniel J. Owens from Liverpool John Moores University where we talked about his current main area of research or one of them at least, which is Vitamin D and the Athlete. He's published with his colleagues, doctors Richard Allison and Greame Close, or Professor Greame Close, who you'll remember from a few episodes back on CBD that I’ve talked to Greame numerous times on this podcast.


So we had a fascinating conversation today about all things relating to vitamin D. What is relevant about vitamin D to athletes? We talked about you know what vitamin D actually is. How does it actually function within the body both in normal people, but also what's relevant to athletes? So we looked at areas like bone muscle regulation, repair muscle function. We talked about the impact that vitamin D has on innate and acquired immunity. We talked about things like exposure to sunshine, ethnicity. Should we test? Shouldn't we test? What does the evidence tell us about vitamin D and how much of that evidence is actually relevant to athletes. And are we able to influence performance through vitamin D are just some of the really fascinating areas that Dan and I talked to in today's episode. 


So you'll hear us talking about various references like this main paper that we covered, his review article on this topic that was published a couple years ago. You'll find that linked on the podcast website, which you can access along with all the other resources that will relate to this podcast. Some of the other podcasts that I referred to or that you will find irrelevant to this conversation that we had today I will also link to in the podcast notes on the podcast webpage where also you'll find in these new episodes that I’m recording uh transcripts where you don't just listen to our podcast. You can also read the transcript and get a double dose of that knowledge, which I hope you find of value. 


Also, while you're looking at our podcast website when you go to, do please have a look at our various other offerings that we do there such as our online diploma in sport and exercise nutrition, our diploma in performance nutrition, which is specifically aimed at training you in a practice-focused system of education for sport and exercise nutritionist, sports dietitians, sports nutritionists, personal trainers and so on who are interested in a high-level of training in education in applied performance nutrition. You can learn all about that on our website. And of course our new software platform, SENPRO, which is a suite, a collection, if you like, of tools, proverbial tools for the proverbial toolbox that you will need to practice as an effective performance nutritionist. Meal planning tools, we've got these cool new performance plates and a wide range of recipe tools and a whole host of business tools that you'll find in SENPRO to help you in your day-to-day practice with individuals or in team sports even. We have a solution for you there in SENPRO.


Anyway, I shall plug those two resources and leave it at that and let you enjoy this episode with DR. Daniel Owens that I had earlier today all about Vitamin D and the Athlete. Enjoy.




[00:04:15] LB: Hi and welcome back to the Institute of Performance Nutrition’s “We Do Science” podcast, the IOPNpodcast. My guest today is Dr. Dan Owens. Hey, Dan. How are you doing?


[00:04:27] DO: Good. Thank you. Thanks for having me.


[00:04:29] LB: It's an absolute pleasure. You and I have known each other a while one way or another. You've contributed quite a few lectures on our program over the years. And as I was just saying off there, which is relevant to our conversation today, you created some other cool content including a presentation I gave on vitamin D, which you'd actually created the slides for. And that's kind of the idea for this chat today came up, because I reread some of that work that we had done a few years ago and then I read your paper that you had published after that on Vitamin D and the Athlete: Current Perspectives and New Challenges with Richard Allison and Greame Close. And of course my listeners will be particularly familiar with Greame Close, because he's done lots of podcasts for us, and one of your close colleagues of course there at LGMU. 


But, listen, before I sort of dive into why I specifically wanted to get into this, and then we can have a good chat. Just give the listeners a bit of an overview as to who you are and what you're up to.


[00:05:34] DO: Yeah. So my name is Daniel Owens. I’m a lecturer here at Liverpool John Moores University in the school of sport and exercise science. So I’m lecturing across a few different degree programs. And then I also have a research profile as well. So we're investigating things, mostly things like vitamin D and also working on some other things with Greame Close as well. And in the past I’ve also worked as a practitioner working with some different teams providing nutrition support as well.


[00:06:01] LB: Yeah, that's brilliant. Like many of my guests on here, you've got that science practice and that sort of translational perspective where you can see where one goes to the other and also inform back to your research, which I always find cool. And that's evidenced when we read this paper, for example, that we're talking about. It's very relevant to informing practice, which is obviously what I’m interested in and what I’m hoping our listeners get the most out of these conversations. 


So, look, in my sort of preamble I was talking about we've done a few things on vitamin D, and it is such an interesting area for reasons that I think most people get anyway, but we're going to really unpack that, and you're the man that's going to help us dig a little deeper and unpack that as we just indicated into practice in particular. What does all this science mean? What's relevant? What's irrelevant? And what should we take from that as current or aspiring practitioners? 


So maybe we could start this conversation off with – I mean why is vitamin D so on point? Why has it become so popular? And I guess in this current climate, for those that are listening to this podcast months or years down the road, this is right in the middle of a pandemic where vitamin C may also have some implications. So we are talking about athletes, but we're also talking about human beings where vitamin D is relevant. I mean why is it such an important and interesting area?


[00:07:31] DO: Yeah. So I think it's important for the general population for a start because most people for most months of the year, let's say from October through to march time, tend not to get enough sunlight exposure, whether that's because of the geographical location or whether it's because of their lifestyle because they live indoors and maybe they were full body clothing, or whatever it might be. 


And as a consequence of that, we don't really produce enough vitamin D. So as we can get into a little bit more detail later, vitamin D is primarily obtained from sunlight exposure. So as a consequence, what we see is large proportions of populations around the world have vitamin D deficiency. So basically low vitamin D levels. And as we've learned over the past must be 30 40 years now, vitamin D has so many different biological roles. So the impact of not having enough of it could be quite serious in some cases.


[00:08:31] LB: Yeah. Well, that's I think what makes this so interesting. And in the same way that human beings vary enormously. Their geographical locations very enormously, where they live at altitude, but the sports, personal preference in terms of how much they wish to expose to the sun. I mean there's just so much to this that's absolutely fascinating. But before we explore those different areas, let's just define then what actually is vitamin D? Because I’m sure people have got an idea. Some may have really researched this area. Some who are less familiar will have an idea that may not be the full picture. So what actually is vitamin D and what makes it so unique?


[00:09:12] DO: Okay, yeah. I mean that's a really good question to start with, because although vitamin D is called a vitamin, it isn't really a vitamin. So it was just called that because at the time the sort of biochemical investigations that were going on were uncovering new vitamins with functions in the body that came from the diet, and vitamin D happen to be one of those. But what we've learned since then is that vitamin D is much more similar to a steroid. And not only that, as I mentioned before, we don't really need to get a great deal of it from the diet, because 80% to 90% percent of it we get from some light exposure. So we actually make it ourselves, which is very different to other vitamins. 


So it's more of a steroid hormone, and as a consequence it can affect any of the tissues in the body that have got the machinery to process it, which happens to be quite a lot. So I guess the takedown there is that it's not really a vitamin. We can produce it ourselves with the correct sunlight exposure and it's more similar to a steroid. 


[00:10:16] LB: And we like to sort of keep technical terms simple as possible. So of course everyone's familiar with the term vitamin D except that it isn't just vitamin D. There are various forms of it, aren't there? And there're various forms that you acquire externally. And then there're things that happen internally. Tell us about that.


[00:10:37] DO: Yeah. So to start with, I guess, the external part is important to consider, and there are two main forms of vitamin D, which are vitamin D2 and vitamin D3. The type that we produce when we're exposed to sunlight is vitamin D3. And most of the dietary sources of vitamin D that we would get are also vitamin D3. There are some sources of vitamin D2. They're a lot less than vitamin D3. And in addition to that, we know that vitamin D3 is about 9.5 times more potent than vitamin D2. So the main one that we're looking to get is vitamin D3. 


When we produce it in the skin or whether we get it from the diet, the fate is pretty much the same in the body. It undergoes a couple of different reactions that lead to it being activated. So the first one happens in the liver and it creates this compound called 25-hydroxy vitamin D or 2,5OHD. And although that sounds like a technical term, it is important to grasp, because if we talk a little bit about measuring vitamin D status this becomes important. 


And then this particular compound gets activated again in the kidney or some other tissues that can do it into a compound called 125-dihydroxy vitamin D, or 1,25OHD. And it's that molecule which actually exerts the effects in the body. So trying to keep technical terms to a minimum, but it is important to sort of pick up on those two key ones.


[00:12:03] LB: Absolutely. And we're going to get deeper into that, because that's what I think makes this so interesting. And as my listeners will hear me say all the time, we need to have a certain depth to our understanding of these things in order to understand when and when not to use them and what we should expect out of these things, which I think from vitamin D is very much an important concept. But as with all these areas of science and medical science and sport and excise science, there's a body of knowledge, some of which is relevant for medical reasons and some of which is relevant for performance reasons. Perhaps you could give us just a wee bit of historical perspective on what actually vitamin D, because we're going to be talking about unpacking the science, the research. But where does that knowledge even come from?


[00:12:55] DO: Yeah. I mean the discovery of vitamin D started because of work on experimental Rickets. So Rickets being a disease by which bones become soft and brittle. We typically see in children. And in adults it's called osteomalacia, but it's essentially the same thing where we have these sort of soft bones as a consequence of not enough vitamin D. And what that research really started to show was that vitamin D is really important for absorbing calcium from the diet into the bloodstream. Now when you've got enough vitamin D, that calcium gets in. It maintains normal calcium levels, which are obviously important for so many things, one of which being bone health. But when you don't get enough vitamin D, you can't absorb that calcium and you start to take it from other places to maintain how much is in the blood. And one of those places is bone. 


So the classical biological function for vitamin D, if you want to call it that, is maintaining calcium levels within the body, and therefore also maintaining bone health. So that's where all of this research really started. But it's developed so much over the years into areas of immunity and also the musculoskeletal system as well. So there are so many other biological functions that we can now attribute to vitamin D that span much further than just bone health.


[00:14:20] LB: Yeah, that's interesting, isn't it? Because, well, if we have this conversation with sports scientists or nutritionists, they'll have a different perspective. But if for example we asked my father, for example. Vitamin D, he will immediately say bones. And that's what I find interesting particularly now that you've given us some historical perspective. And yet of course I think what's really key here is it's so much more than bones. And in fact we'll get into the relationship that vitamin D and bone has, which we have explored in other podcasts like I’ve done with Craig Sale and Kirsty Elliot-Sale about nutrition, exercise and bone health and so on. But this is one of these areas like in your paper that we just referenced, you've got a section on this where you're referring it to as being on trend in sports nutrition nowadays. So it's not just a health thing. It's not just the bone thing. There's so much more to that. And I’m going to come back to that, because I think before that becomes a relevant conversation, I think I'd like to delve just quickly back into what actually vitamin D does and the different areas in which it exerts its influence. 


[00:15:28] DO: Yeah, sure. So I think in order to have an appreciation for that, we need to first sort of understand how vitamin D is actually exerting any of its effects in the human body. And it does that in the same way other steroids would do. It binds to a particular receptor, which is specific to it and then exerts a number of different effects. And that is only going to happen if a cell or a particular tissue expresses that necessary machinery. So if it's not there, it's not going to have an effect in that tissue. 


And what we know is that so many different tissues actually express the machinery or the receptor for vitamin D to exert its effects. We know that bone cells have it, muscle cells have it, immune cells have it and so many different cell types have it. And what happens when these two things interact? It can also interact with our DNA and it changes basically the function of our cells in simple terms. So obviously different tissues and different cells have different functions. So that's going to be specific to the cell type. But we know for example that in muscle cells, vitamin D is going to up-regulate certain things that are responsible for muscle growth, maintaining muscle repair as an example. 


[00:16:43] LB: So I think one of the things that stands out to me particularly when you start looking into this sort of area of this body of knowledge that there is on vitamin D, there's sort of a misinterpretation as to where vitamin D lies in the sort of requirement hierarchy of need. If you go into a food supplement store or look online, you're given the idea that vitamin D is this sort of panacea for all sorts of issues. And we'll even delve into what it may or may not do specifically for athletes. But maybe you could help us understand the difference here as it relates to vitamin D. The difference between something that's required necessary, essential as opposed to something that could be maybe ergogenic, for example.


[00:17:33] DO: Yeah. So that's a really key point, and that'll eventually come back to the recommendations that we might talk about later. Vitamins are absolutely required in the diet in the sense that if we don't get them we develop a deficiency, which means that there's some sort of health implication of not getting them. So in that sense, vitamin D can be considered a vitamin, although structurally it isn't. But if we don't get it, we develop deficiency. We develop health problems. 


So the key thing that we have to think about here is maintaining vitamin D status. We're not trying to go for some super physiological level, which you might think of with things like creatine or other supplements. What we're trying to do is just maintain levels that are considered to be normal and then that allows any of the tissues that require to do their function as they normally would. But if we provide more, it's not going to do any better. It's just going to do what it's supposed to do. So that's a really important thing that I think any practitioner, anyone working in this area needs to think about, because you'll know yourself. When you talk to athletes, oftentimes we might talk about a particular nutrient. And if we tell them it's good for one thing, they might think that having 10 times more of it is even better. If you give me this much, well, I want to take five of those pills instead, because I’m going to be even better. But it's really important that we convey the message that more is not necessarily better when it comes to vitamin D.


[00:19:01] LB: Absolutely. I'll add one to that, which is normal isn't necessarily normal. What even is normal? See, that's one of those words that crops up. And you see this in reference ranges. Well, from the perspective of a practitioner, Dan, how am I supposed to determine what actually is normal? And I guess there're two sort of angles there. You've got what constitutes as, I guess, a normal person relative to normal reference ranges? Or are we supposed to look at different reference ranges? But also, I guess, what are the different scenarios that it doesn't become normal even if it is normal? Help me with that one.


[00:19:41] DO: Yeah so I guess a useful place to start is to consider what the different levels or the different categorization of vitamin D status is that's considered deficient and adequate and what all these different terms mean. The categorization is generally accepted by dietitians, physicians and so on, is the US Institute of Medicine, they're now called the National Academy of Medicine, I think they've changed their name, their guidelines for vitamin D status. 


So first things first, we measure vitamin D in a unit of nanomoles per liter. So that is accepted worldwide instead of referring to it micrograms or whatever it might be in the blood. Let's just think about it as nanomoles per liter. And the reference ranges are they span from severely deficient, which is less than 12.5 nanomoles per liter. Deficient being 12.5 to 30. Inadequate, which is 30 to 50. Adequate, above 50. And some people suggest that above 75 might be needed for optimal function. So these guidelines were developed a long time ago based on this early work on bone that we talked about. But now that we know a lot of other functions for vitamin D, it seems that – Or maybe they might need a little bit of adjustment. So if we're thinking about normal, for the most part we consider that to be above 50 nanomole per liter. Anything less it means you probably haven't got enough. 


[00:21:16] LB: So I’m going to come back to some of that in a minute, because another sort of phrase I come up with often is why guess when you can test? Which I think is an important issue here to test. And not just guess, but not everyone can do that. And actually there's a decision that comes before testing, which is do I need testing? So what are going to be the risk factors that might lead someone into some sort of vitamin D inadequacy? Because there's a spectrum there as well. 


[00:21:44] DO: Yeah, absolutely. So anything really that limits sunlight exposure is going to be a risk factor. So the first one that you can think about is geographical location. So the further you live north of the equator, you're going to see less sunlight for more months of the year. And the same goes if you are quite south of the equator. So let's say 40 degrees south, which is sort of Tasmania, New Zealand, that sort of area. So if you live in these regions you can say that probably from October to March you're not going to see enough sunlight to produce vitamin D. 


Now some people have often asked, “Even on a sunny day in the winter, then am I not going to produce vitamin D?” And the answer is no. And the reason for that is because where the sun is in the sky, it's too low and such that not enough of the ultraviolet radiation from the sun can actually reach the earth's surface. So even if it is sunny on Christmas Day, we're not going to be producing much vitamin D at all.


[00:22:41] LB: I think we're saying sort of high and low. Are you talking about the angle, the zenith angle or whatever it is? 


[00:22:48] DO: Yeah. I mean the technical term is solar zenith, which is basically just that angle of the sun. And the lower it is in the sky, the less chance you have of producing any vitamin D. Some people say that, “Look, if your shadow is longer than your height, then you're not producing any vitamin D. And if the sun is so low and if you've got no shadow at all, then you're not producing any, because there's no sunlight to produce a shadow.” 


[00:23:11] LB: Because this is an area I find fascinating, because people make assumptions. Don't they? Oh, well I went for a jog in my T-shirt. My skin was exposed. It was sunny-ish. Even in England you can make that claim occasionally But actually you shouldn't make those assumptions, should you? Based on what you just said.


[00:23:28] DO: Exactly. And that's really important to consider. So it was nice here in Liverpool today, which is rare. But if I went for a run during my lunch hour, I certainly wouldn't have produced any, much at all, of any vitamin D, because we're getting right close to December where the angle of the sun is so low that we're not going to see enough ultraviolet b radiation. 


Another point on that which links to it quite well is that skin pigmentation is also going to affect it as well. So if we think about the summer months now where we might be seeing enough sunlight exposure and enough to actually keep us vitamin D sufficient, the darker skin you have, the longer you would need to spend in the sun to produce enough vitamin D to make you replete. 


So there's some really nice research out there which is categorized skin colors on a scale of I think it's one to five. So going from quite light to quite dark. And basically for the same time exposed to UVB radiation, darker skinned individuals produce less vitamin D versus lighter skin individuals. So skin pigmentation is going to play a role. Even if you are light skinned, if you put a lot of sunscreen on, that's also going to block it out as well. As well, clothing being indoors. You get the idea that anything that's going to stop the UMB actually reaching your skin is going to limit your ability to produce vitamin D.


[00:24:53] LB: Yeah. I mean that's pretty shocking for some people though because they think they've got it lit just by going outside on a bright winter's day. And like you just said, and I'll just summarize those factors, because I think they're important. Anything from skin color, latitude, the amount of time you spend indoors, which face it, in our sort of moderately cold environment, particularly during lockdown, we're indoors a lot. But also if you're in a seriously hot environment, you're probably indoors because it's too hot to be outside even though it's perfect sunshine. You might get fried. Or you deal with that by slapping on some sunscreen. And invariably you're wearing some element of clothing. And if that isn't enough, the season is a factor. So that all adds up to me like an extremely high likelihood that there could be an issue.


Now before we get into how you can determine your own personal or an individuals or a teams or whatever vitamin D status. What about variability between individuals? Because, yes, there's color of skin and so on. But presumably, there's some degree of variation as well between individuals. What does the evidence tell us about that?


[00:26:04] DO: Yeah. This is an area that requires a lot more research in my opinion because there are invariably going to be some genetic factors, which influence how well we produce vitamin D. How well we use it. How well we transport it around the body. So at the moment, there isn't a great deal of understanding about why there's variability between individuals who might be exposed to the same amount of sun or vitamin D in the diet. But we do know that there are different genetic variations in some elements of the vitamin D system within the body. So I would assume over the next sort of you would think five or ten years that we're going to see a lot more on this particular area. 


One thing that sort of is emerging in the literature and some ideas have been popping up, there're only a few papers on this, is your body composition might actually play a role in this. This is probably something that when you look back at some of the work I wrote in the past probably wasn't covered, but it's certainly important now. What we've seen is that we know vitamin D can be stored in our fat, in the adipose tissue. And some studies have shown that when you exercise, acutely after that exercise bout you see a little bit of an increase in your circulating vitamin D. That is quite well associated with your ability to break down the fat, break down that adipose tissue. So some of the theories at the moment are that we can store some vitamin D in our fat and it can be released into the circulation when we exercise. 


There is also some evidence that it can potentially be stored in muscle as well. So that has more implications. And Professor Greame Close and myself talked about this in the past that we've seen in some cohorts of rugby players who have a lot of muscle mass. In the winter months a lot of them actually have quite high vitamin D levels and it could actually be that the ability to store it in muscle and release it when we exercise could be a way of maintaining vitamin D status. But at the moment that's kind of theory and it still needs to be experimentally proven.


[00:28:11] LB: Yeah, but interesting. Because of course as we just pointed out, even our ancestors who didn't muck around with sunscreen and get worried about needing air conditioning and all that hundreds thousands of years ago, whatever, they still did exist in a seasonal environment. And yes, there were times of the year where they had optimum exposure through hunting and gathering and getting plenty of sunshine and exercise, but obviously they had times of the year where they didn't. So it obviously makes you think, “Well, does that matter?” 


And I’m mentioning this because we're going to talk about how do you actually test them. What is the relevance of that reference range when if there are seasonal changes, if you like, in vitamin D levels, do we have a static requirement for vitamin D? Or is it okay that it goes up and down? Or is there, like you mentioned, some magic storage somewhere that helps us get around that problem?


[00:29:04] DO: I think that's a really good question and it's something that I’ve been thinking about recently when designing new research studies. So I’ve got a student at the moment doing a little bit more work on this idea that it can be released from adipose tissue. And some of the thinking behind this is will that change the way that we prescribe vitamin D through the winter? At the moment, as I say, we obviously need to experimentally determine this. But it does raise that question that we've obviously said, “Okay, seek sun exposure in the summer, and then we can supplement through the winter.” But will that change when we learn more about this? I think that's a really exciting area in vitamin D research at the moment.


[00:29:44] LB: And just because it's popped in my head as you're saying it. With certain things, I am thinking, say, with alcohol, for example, when you consume alcohol at relatively high levels for a certain period of time, you get to a point, I think it's called tachyphylaxis or whatever where you have to consume even more to get the same effect. Perhaps that's an issue with exogenous vitamin D or ingested vitamin D as opposed to those other, well, exposure to the sun maybe? I don't know.


[00:30:14] DO: Potentially, I mean there are so many areas of, I guess, vitamin D biology that are not that well understood at the moment. So the regulation in terms of storage and release and exercise and how we supplement, although we think we know quite a bit, we don't. There's still a lot more to understand.


[00:30:32] LB: More questions than answers, right?


[00:30:34] DO: As always.


[00:30:35] LB: As always. All right. Look, let's just quickly talk about the whole testing thing, because I find this area interesting, because again there are assumptions made with this. And then we'll lead into maybe some of the more functional roles of vitamin D as it relates to what's relevant to the athlete, because that's in itself interesting. But there's no point going there until we actually determine do we even need vitamin D? Are we even deficient? 


So like I said, why guess when you can know? And the way you can know is through testing. But not all methods of testing are accurate like in everything. We hear this with the COVID testing. There are all these tests, but they don't necessarily work. There're different levels of confidence we should have in these testing. Tell us about how do you even get tested in the lab or in a practice setting? And how confident should we be of that information and how relevant is it?


[00:31:28] DO: So the way in which we're going to test is, is from the blood. So first of all we need to somehow draw a blood sample. And we can either do that by taking a venous sample, so directly from the vein. Or blood spot samples, we can use as well. And they have been shown to have good agreement with the venous samples now, which is brilliant, because they're a lot easier to obtain. Once you've taken the blood sample, the method then by which you, I say, for vitamin D is really important. So there's plenty of research out there now to say which is the gold standard method. And the gold standard method is mass spectrometry. So we should always be aiming for that. Other methods tend to either overshoot or undershoot. And the variability from one test to the next can be quite large. Whereas with mass spec, it's really sensitive and reliable. So we're going to be measuring the right thing and we're going to get consistent results if we use that method.


In our labs we tend to take it from the vein, and we use a hospital lab that has developed a lot of the assays for vitamin D. But that's just because of a research relationship. You can actually do that on the NHS and they will use mass spec as the method to determine it as well. So if an individual, anyone in the public wanted to do it and they you know they were just interested rather than being referred by their GP or something like that, you can order home vitamin D test kits from Birmingham University hospitals online. I think they're around about 40 quid or something like that. And they send you everything you need to take your sample yourself. It's a finger prick sample. You dot it on some paper, send it off in the post and they'll do the assay on the drive blood spot. And that will give you a really reliable measure of your vitamin D status.


And just to sort of give a little bit of I guess detail about what is actually being measured. As I kind of alluded to at the start, the reason for saying 25OHD or 25-hydroxy vitamin D is important to know is because that is the thing that we measure in the blood as the marker of vitamin D status. And the assay is basically a sum of 25OHD 2 and 25OHD 3. So our some exposure to vitamin D is captured by that particular method.


[00:33:42] LB: Okay, that's awesome. So there's different ways of getting tested. And of course not everyone's based in the UK. There are listeners are all over the world. But there's a very high chance that you have pretty decent accessibility to testing. Please don't contact me to give you links or anything, listeners, because it's going to be all sorts of options for you. But I will put a link to the one that Dan mentioned, because I use those actually, the blood spot. I used to use them in practice. I don't have much time to practice currently. 


All right. So clearly you need to test. Just out of interest, what are the consequences of making decisions with some sort of supplementation of vitamin D without actually knowing what your levels are whether you need it or not? What are the consequences of that?


[00:34:30] DO: I mean, first of all, if we test we're going to have a better idea of what we need to do in terms of how much vitamin D we might want to supplement with to correct the deficiency. If we were going to just blanket supplement a group of people without knowing what the vitamin D levels are like, there is the chance that you're going to start giving vitamin D to people who have already got enough circulating in their body. 


Now, with the sort of recommendations of doses, which I guess we'll talk about shortly. It's unlikely that we would cause any real health detriment. So we wouldn't likely see toxicity from given a couple of thousand international units to someone who's already got enough vitamin D. But what Greame and myself have shown in some past research is that you can start to increase the breakdown of vitamin D, which in turn might actually influence how effective the supplement actually is. So you might be having the opposite effect of what you aim to do in the first place. 


So I think the key thing really is that people shouldn't be too worried that they're going to cause any harm per se, but we might not be getting the optimal function out of it if we just blanket supplement to everyone. 


[00:35:41] LB: Yeah. The only caveat I’ve got to that, and this is something that I’ve actually seen in my own practice in working with an elite football team where one of the players whose English was not their first language had been advised by the team doctor to take a significant dose of vitamin D once a week. But because most people think they do these things every day, this player had assumed that that dose was something they should take every day. And I guess it's like with anything, we just got to be absolutely clear that our recommendations are actually understood by the individual. Anyway, I just thought I'd add that in, because it is actually a scenario.


[00:36:23] DO: Yeah. I think that's a nice case study of where things can go wrong particularly when athletes haven't quite understood the recommendation. It also highlights why given a really high weekly dose isn't that effective. Now our research has shown that experimentally. But just on the anecdote that you provided there, an athlete might take that and then do it every day, and that's when it can become a bit of an issue. 


I guess if you really didn't have the capability to do the testing though, one of the things you could do is determine all of the risk factors that the athlete might be experiencing related to obtaining vitamin D. And then also really drill down if they are getting any vitamin D from a supplemental form, even if it's a multi-vit that they might not think it's in, from a fish oil, from something the doc's giving them or a jab or whatever it might be to really determine are they actually getting it from anywhere else. 


In addition to that, one thing that often gets overlooked, and I’ve seen this in practice, is the use of sunbeds. So the UVB that you get from using a sunbed will increase your vitamin D. That's one of the benefits as well as being tanned. We know there are a lot of detrimental effects to that sort of level of exposure to UVB, but it will increase your vitamin D. And in the past we've tested players who said, “No, I’m not taking any vitamin D. I’m not taking this supplement or that,” but their vitamin D is really high. And we've kind of been scratching our head and then said, “Are you sure you're not like using sunbeds or anything?” They’re going, “Oh, well, once or twice.” And so it comes out. And you’re okay, “That's where it is so.” But the flip – 


[00:38:00] LB: Football players. 


[00:38:00] DO: Yeah. So the flip side to that though is know some individuals don't even appreciate that using a sunbed, for example, would increase your vitamin D. So again it comes back to education like everything that surrounds nutrition and applied practice. We need to make sure that the messages has been crystal clear and received by the athlete.


[00:38:23] LB: Absolutely. Well look, let's move on from that into why vitamin D in particular might be relevant to athletes, who of course our listeners are primarily performance nutritionists, sports dietitians, researchers, students and or athletes themselves potentially. So you've outlined in your paper, for example, there are a number of sort of indirect and direct effects. But I guess just so I can make sure we cover the main ones here, one of the areas that you talk about is muscle repair and remodeling. So what's happening there?


[00:39:04] DO: Yeah. So we've known for a while now that muscle is responsive to vitamin D, which means that it's got all of the machinery to be able to take vitamin D in, use it or convert it to its active form and then use it. So we know it's a target if you will for vitamin D. Some of the work I did during my PhD added to this body of research by showing that in individuals who have got low vitamin D status, their recovery from damaging exercise is slower than those who have been supplemented to improve their vitamin D status. And then we tried to take it a little step further to develop some of the cellular mechanisms by which that happens as well. So it looks as though vitamin D can influence the stem cells that are responsible for repairing muscle. 


Interestingly, in the past couple of years, so since I wrote the review that we're talking about, there has been some new evidence showing basically backing up that early research. The stem cells in the muscle are definitely responsive to vitamin D and might be responsible for some of the beneficial effects that we see the vitamin D in muscles. 


[00:40:12] LB: And when you say beneficial effects though, what you're meaning is adequacy as opposed to deficiency, right?


[00:40:18] DO: Yeah. That's a good point. So beneficial effects compared to if you didn't have enough vitamin D. Absolutely. So it's not ergogenic in any way. So the key take home here really is that if you are involved in a sport where you might experience muscle damage or, let's say, contact type of damage, rugby being an example, the muscle has to undergo some sort of repair process, which is a really nice and interesting feature of muscle is that they can repair itself. But so many different factors can influence that repair process. And what we're saying is that we think vitamin D is important for that process. So if you don't have enough of it, the process might be impaired slightly.


[00:41:00] LB: And yeah, this is great, because key role I feel we have as performance nutritionists is it's not really about performance, it's about just keeping them healthy, keeping our athletes healthy and robust. And it's not just about how can we return them to play, but how can we prevent them from falling apart in the first place. Given more legs so to speak, which I guess segues into this idea that vitamin D isn't ergogenic, but does it nonetheless still play a role in how the muscle actually functions given skeletal muscle is a key area of interest in an athlete? So is there something there that is relevant from a performance perspective you think?


[00:41:40] DO: Yeah. Again, this is an area that's a little bit more ambiguous in the sense that there have been studies that have shown a beneficial effect of maintaining your vitamin D status and some that don't show any effect really. And I guess one of the things that has hampered that research is that people's classification of what is low and what is adequate has been a little bit muddied and it's not really conformed to one particular categorization. 


For example, in our lab before I even started my PhD, Greame Close and James Morton and some of the other guys here did a little bit of work looking at some basic outputs of muscle performance and sort of 30-meter sprint times, bench press, squat, that sort of thing. And what they actually showed was that if they took people from pretty low vitamin D levels to adequacy, they actually saw an improvement in these different outputs that are reflective of muscle function. 


I guess it's best been summarized in a meta-analysis that came out, and I think it was 2015, which basically showed that it seems that you have to have pretty low vitamin D levels in order for muscle function to be affected. And it seems that you probably need to be in the range of less than 25 nanomole per liter, which is getting to the range close to severe deficiency until you actually see an effect on muscle function. So if it's going to have any effect at all, I think it might be at the more severe end of deficiency. 


[00:43:12] LB: Yeah. And I guess as people are already getting from this, it's just the sheer broad spectrum of issues that deficiency or at least inadequacy of it leads you down a path you don't really want to be going, right? And I guess one area from that that I find really interesting is the impact that, well, I guess nutrition generally about vitamin D very much now we know impacts innate and acquired immunity. And this is something that was mentioned in numerous podcasts I’ve done, Neil Walsh and also Mike Gleason, just to name two, and both of them are coming back hopefully. Well, Mike is coming back very soon on the podcast. But they both mentioned the importance not to overlook vitamin D. But also in Professor Walsh's concept of looking at the bigger picture of lifestyle rather than just one area. But tell us, if we're going to be a bit reductionist about this, I mean why is vitamin D important to immune function?


[00:44:14] DO: So like the other tissues that we've talked about, the immune system has the capability to use vitamin D. It's got a vitamin D receptor and it's got some tools to be able to convert it to its active form. I guess from a historical perspective, a lot of the interest around vitamin D and immunity was stimulated by a study that was done a long time ago, which basically showed that the incidence of the sort of winter infection increase coincided really nicely with the reduction in vitamin D levels. So people started to say, “Is this a cause-and-effect relationship?” 


And what subsequent research has shown is that both the innate and acquired immune system as you've correctly said are responsive to vitamin D and it mediates so many different aspects of innate and acquired immune function. I think Neil talked with you about that on one of your recent episodes. And I just had a chat with him. Actually, he's here next to the office next to me today and we were having a chat about this area. But I think one of the key things to take home from this, which Neil has published in one of his recent articles, I think was the sports medicine review, is the idea that vitamin D is a tolerogenic nutritional aid in the sense that it might not necessarily prevent you getting the infection. Now, there are some data that might disagree with that, but it might not necessarily affect you getting it, but it's going to influence the infection burden. And that basically means how severe are the symptoms and how many days are you going to have those symptoms for? And that's been shown in the general population, but Mike Gleason has also shown that in athletes as well. So basically the athletes who have higher vitamin D levels have a lower infection incidence and their symptoms are less severe and for fewer days than those who have replete vitamin D levels basically. So I think the evidence is really strong for that, and that's one of I guess the key reasons why we try and optimize vitamin D status for our athletes.


[00:46:18] LB: Yeah, it's an on-point conversation for what we're all currently going through. I think it's in everyone's best interest. Particularly, I said right at the beginning, and I say this often, athletes aren't just athletes. They're also human beings. But every single human being who this COVID pandemic is affecting one way or the other are also largely likely to have some degree of an issue with vitamin D status, which I think maybe one of the good things that might come out of this pandemic is an increase in an interest in these areas so that we can really learn about how – Like you say, maybe not about disease prevention, but our ability to tolerate an infection and actually get over it. We might get the sniffles, but it won't kill us necessarily. I think it's fascinating. 


Of course athletes who, particularly, like endurance athletes, ultra-endurance athletes or even intermittent sports athletes, but those that are have high volumes of training and competition, they're just wearing themselves down, lack of sleep, over training. You add in that inadequate or even a deficient state of vitamin c, and it's a pretty bad combination, isn't it? It’s sort of a scenario that's bound to result in problems, which is why we're interested in this.


[00:47:32] DO: Absolutely.


[00:47:33] LB: Right. So something else that all humans and athletes have is a heart. And it's quite interesting. A few years ago now, but I did a really interesting podcast with professor Greg White who is also the chief examiner for my own doctorate, which just brings back interesting memories of how Greg is about evidence and so on. But we were talking about the athlete's heart and a sudden cardiac death, which is a an interesting phenomenon that does occur more often than we would like to think to. But other than you know standard concerns over things like heart disease and people eating badly. So they're furring up their arteries and so on. Of course, the heart is a muscle as well. It undergoes a fair amount of pounding in certain types of sports in particular. How does cardiac structure and function become of interest when we're talking about vitamin D?


[00:48:27] DO: Yeah. So this comes back to some of the work uh done by Richard Allison, who was a co-author on the review that we're talking about here. And whilst Rich was out in Qatar, he did some research on a large cohort of athletes. Actually I think sort of 800 plus looking at cardiac structure in these athletes basically. And we know that one of the beneficial adaptations of being trained or exercise training is a structural and electro physical improvements in cardiac structure. So we basically see an increase in the muscle size of the heart, okay? And particularly in the left ventricle. And basically what Richard showed was almost a stepwise increase in the size of the heart with each level of vitamin D status. So if you've got really low vitamin D, they have the smallest left ventricular size. And as you got higher up, you've got bigger, stronger hearts. So that was a really interesting finding, and of course a really well-powered study as well in over 800 athletes. 


So I think that's one aspect of it. We also know from some work on animals, which obviously the translation isn't as great as of course working in humans. But we know that energy metabolism in the heart as well is affected when they have low vitamin D diets. So this was in a rat model I think from a long time ago. So there's a reason for both the structure and the function of cardiac tissue for vitamin D.


[00:50:00] LB: Yeah, fascinating. Fascinating. Well, look. We haven't got a whole lot of time left here. So I do want to mention, but we don't need to get too deep into bone health and fracture risk only because I’ve done an entire podcast just on this topic with professor Craig Sale and Kirsty Elliot-Sale. But we should quickly get into it. What's relevant to bones and fracture risk when it comes to vitamin D? 


[00:50:23] DO: Yeah. So I mean, okay, a couple of key points. One obviously we talked about earlier, which is that vitamin D regulates calcium homeostasis in the body. So clearly it's important for me maintaining normal calcium levels. I guess the pitfall of all of this and the conundrum is that Richard again did a nice piece of research in a large cohort of athletes. I think this time over 900, which basically showed no relationship between vitamin D status and bone mineral density, so a marker of bone health. And one of the reasons that has been postulated for that is potentially that the stimulus of exercise, known as the osteogenic stimulus, which gives us stronger bones, might actually override the effects of low vitamin D status in athletes. 


So the athletes that might be at most risk are those that potentially don't have such an osteogenic stimulus, those that are not weight-bearing exercises, for example. So jockeys are a great example that Greame’s will have talked about in the past. I’m not aware of any research on this, but potentially swimmers that are not doing a significant amount of weight training. Obviously, those that do, that could also act as an osteogenic stimulus. But really it's the weight-bearing activity that seems to override the negative effects of low vitamin D. 


[00:51:45] LB: Now since we talked about bones and we've also talked about how various either environmental factors and/or individual characteristics within humans like skin color, for example, the pigmentation. Certain assumptions are made when you start talking about these things. And of course what's emerged from that is what you referred to in the paper as the black athlete paradox, which is really interesting, because it does bring out this point of not making assumptions about these things. What is it that I’m referring to there and why is that relevant to listeners to understand this? 


[00:52:22] DO: So there's been some research that came out basically showing that despite black athletes having quite consistently low vitamin D levels, they don't present with the negative outcomes of typical vitamin D deficiency. So in fact they have some of the highest bone mineral densities even for lower vitamin D status, which doesn't really make sense then. That's why we call it paradoxes, that they've got low vitamin D but all of the things that we associate with low vitamin D don't seem to be affected in this group of individuals. And there have been a number of different explanations for this. 


One of them that came out was that potentially the fraction of the 25OHD that's circulating in the body that is considered to be free, so it's not bound to anything else in the blood, is more important as a marker of vitamin D status than measuring the whole thing. And what some of that early research showed was that black individuals actually have a higher amount of this free fraction versus the total amount versus if we compared that with Caucasians, for example.


What we've learned since then is perhaps some of the methods in those papers were a little bit flawed. So we don't actually know anymore whether it really is the free fraction in black individuals, which is attributing to this higher bone mineral density or all of the outcomes that we associate with vitamin D. But what we do know is that 25OHD isn't acting as a particularly strong marker of vitamin D status in these ethnic cohorts. So we're still searching for what could be the best all-round marker of vitamin D status. It might be the free fraction and it might be a mixture of other vitamin D metabolites that are informative.


[00:54:15] LB: Brilliant. Well, I think – Look, we, for the last hour or so, pretty much argued. I'd say you've argued a very good case for why we should be taking an interest in this. I think it's clear. We need to revisit this after researchers like yourself will add and clarify the body of knowledge. But we're going to sit here, right? The listeners are going to be going, “Great, I want to take this. I feel there's a good reason to take it.” Maybe just some sort of recommendations from you that I realize it's difficult. We've talked about we've got to individualize this. But just some general recommendations as it relates to vitamin D for active people. What would you say to them?


[00:54:58] DO: So given the time of the year that we're in now, we're getting into winter months, or at least we are here in the UK. So during these winter months, supplementation of one to two thousand international units per day is going to correct for most deficiencies and it's going to maintain your vitamin D throughout the winter. It's important that that's taken daily as opposed to weekly or monthly in a higher dose based on some of the research that we've done. And if you do that, it's unlikely that unless you’re repeatedly using sunbeds or getting vitamin D from anywhere else that it's going to cause any harm, any toxicity or any issues like that. So it's a pretty safe routine to get into that might give you some really good benefits during these winter months.


For individuals who are in the summer months, so in the southern hemisphere, and for when we get into the summer months, we typically recommend that first of all you don't burn in the sun, okay? That is not good. And we know that it's associated with an increased risk of skin cancer. However, sort of 15 to 30 minutes arms and legs exposed to the sun per day is going to maintain your vitamin D throughout the summer months and it's going to lead you into the winter with a pretty good level of vitamin D that you can maintain. 


So it's important that in those summer months we're not hiding from the sun, but we're not over doing it and burning and looking like the red Brits on the beach abroad. So they'd be my key recommendations. The only other thing I would add to that is if you're working with athletes, you're a practitioner, as with anything that's supplemental, we need to be making sure that we're getting this from a reputable source and a trusted source. So basically when I say reputable, somewhere that can provide you the information the amount of vitamin D that they're saying is in the supplements is actually in it, but also the safety part of it, which is that it's tested and it's free from any other and contaminating sources that might put the athlete at risk. So that would be – Hopefully that was clear enough and in bullet point form, but they would be my key points.


[00:57:08] LB: That's brilliant. Well, look. Thank you, Dan. There're all sorts of areas I think we could have got into, but quite frankly I think everyone should read the various resources that we've referred to. And I will put those links to the podcast page for this particular episode and there will be a transcript and various other things. But there're plenty of resources for people to really geek out on should they want to dive deeper. And if they want to follow you and your research in more detail, how do people access you, your social media, your research gate? What are the ways in which to follow you?


[00:57:41] DO: Yep. So I have a research gate. It's a big long link. So I'll just send that to you. Twitter, my handle is @Dan_Owie. It's Dan_Owie. And I also got LinkedIn as well. So you should be able to find me and feel free to message me. And if anyone wants any advice, happy to jump on a call and talk you through any of the things that we've discussed here. 


[00:58:04] LB: That's brilliant. Thank you so much for your time, Dan. I personally really enjoy these conversations with people like yourself, but I’m sure the listeners will benefit hugely. And hopefully time was well spent listening to our conversation. Just to reiterate, I will put links to all of this on the podcast page, which is you can access that just via our main website at and just follow the links from there. 


Anyway, thank you, Dan. Thank you for your time today. We're at the end of that conversation. I am Laurent Bannock, of course, and I look forward to bringing another episode of We Do Science back to you all very soon. Take care, everyone.