ZOE Science & Nutrition - Do vitamin D supplements work? | Prof. Tim Spector and Dr. Federica Amati

Episode Date: October 10, 2024

Vitamin D is the world’s favorite supplement. Governments around the world recommend people take the supplement for at least six months out of the year. But do we really need these pills? Do they even work? And could they actually be harming us? In this episode, two ZOE scientists - Professor Tim Spector and Dr Federica Amati reveal the truth about vitamin D. Tim is scientific co-founder of ZOE and professor of epidemiology at King’s College London. Federica is head nutritionist at ZOE and author of the Sunday Times bestseller ‘Every Body Should Know This’. 🥑 Make smarter food choices. Become a member a zoe.com - 10% off with code PODCAST 🌱 Try our new plant based wholefood supplement - Daily 30+ *Naturally high in copper which contributes to normal energy yielding metabolism and the normal function of the immune system Follow ZOE on Instagram. Timecodes: 00:00 The sunshine vitamin 01:50 Quickfire questions 04:05 What is vitamin D? 07:12 Is sunlight the best source of vitamin D? 09:40 Does vitamin D keep my bones strong? 15:34 Are vitamin D levels a marker of good health? 20:00 What counts as normal levels of vitamin D?  24:42 Supplement controversy 29:10 Do calcium supplements help bones? 31:29 Can I take too much vitamin D? 37:50 Could vitamin D prevent these health conditions? 42:54 Tim’s sunscreen controversy 46:46 Vitamin D and immunity Books by our ZOE Scientists: The Food For Life Cookbook Every Body Should Know This by Dr Federica Amati Food For Life by Prof. Tim Spector Mentioned in today’s episode: The VITAL Trial - Principal results of the VITamin D and OmegA-3 TriaL (VITAL) and updated meta-analyses of relevant vitamin D trials (2020), published in The Journal of Steroid Biochemistry and Molecular Biology Cut-points for associations between vitamin D status and multiple musculoskeletal outcomes in middle-aged women (2016), published in Osteoporosis International Assessment of the genetic and clinical determinants of fracture risk: genome wide association and mendelian randomisation study (2018), published in British Medical Journal Other ZOE Science & Nutrition episodes to try: What to eat to avoid osteoporosis with Prof. Tim Spector & Prof. Cyrus Cooper | Listen on Apple or Spotify Mushrooms as medicine: Uncovering the health secrets of fungi | Listen on Apple or Spotify Have feedback or a topic you'd like us to cover? Let us know here. Episode transcripts are available here.

Welcome to ZOE Science and Nutrition, where world-leading scientists explain how their research can improve your health. Vitamin D, also known as the sunshine vitamin, it plays a crucial role in the health of our entire body, from bone fractures to cancer. But there's a dark cloud looming over the sunshine vitamin. Some are calling it an ignored epidemic. A reported one billion people have low vitamin D levels, with almost half of us now classed as dangerously deficient.

It's no wonder that so many people are reaching for the supplements. But are we swinging towards too much vitamin D? Recent years have also seen an increase in people hospitalized with dangerously high levels. Our vitamin D intake is a tightrope walk. On one side deficiency, and on the other side intoxication. Today we're joined by two of Zoe's best scientists to steady us during this balancing act. Tim Spector is one of the world's top 100 most cited scientists, a professor of epidemiology and my scientific co-founder at Zoe. I'm also joined by Dr Federica Amati. Federica is a head nutritionist here at Zoe, a scientist at Imperial College London,

and author of the best-selling book, Everybody Should Know This. You'll finish today's episode knowing exactly how much vitamin D you need and where you can get it. Tim and Federica, thank you for joining me today. Thanks for having us. So you know the drill. I don't need to tell you the rules. We're going to jump straight into the quickfire questions.

Are we ready to go for it? Ready. Tim, is vitamin D a vitamin? No. That's going to be a big surprise for many people. It's a good start. Federica, can vitamin D deficiency increase your risk of developing cancer? Possibly.

Can you be vitamin D deficient without experiencing any symptoms? Unlikely. Tim, can vitamin D supplements be bad for your health? Sadly, yes. And then finally, maybe for both of you, what's the biggest misconception about vitamin D in your opinion? In my opinion, the biggest misconception is that it's a panacea for all ills. It's not. I would say that taking more of it is going to give you great benefits. And there's no evidence for that. I think that's going to already shock a lot of people, all this feedback.

I mean, I'm already still reeling from vitamin D is not a vitamin. So that's already like quite confusing. And I know there is a lot of buzz about vitamin D in the media. And I've noticed sort of more and more vitamin D supplements and fortified foods, you know, the grocery aisles. But I've never really understood what it was. And I thought I at least understood it was a vitamin and apparently it's not even that. So, you know, I definitely want to start at the beginning. But before I do that, I just want to sort of tell our listeners, I think they're in for a bit of a treat because

Federica and Tim have slightly different views about what the scientific evidence tells you about vitamin D. And this is sort of, I think, a window for a lot of our listeners into what it's like to be at Zoe and try and take the latest cutting-edge science and turn it into real advice. Because one of the things I've learned is if you ever meet someone who is absolutely categorically convinced about what the science says about something, they're not probably a leading researcher because they're always telling me, well, it's a bit nuanced and there's this other study. And so I think today will be quite fun to understand what does the science really tell us and understand how world-leading scientists like Tim try and pass the latest

evidence to understand what might that mean for regular people like me trying to figure out what to do. So if vitamin D is not a vitamin, what is it? It was misnamed a long time ago. And a definition of a vitamin is something that the body cannot produce itself. And you only need minute quantities in order for it to be effective and keep your body going. And so real vitamins are things like the B vitamins that are key for chemical reactions in the body and our cells that basically keep us alive and that we can't generate them themselves

and so we have to get them from our food. And that's why vitamin D, as we call it, doesn't meet those criteria because it's actually in huge amounts compared to the small amounts you need for vitamins already in its natural form. And the body synthesizes itself via sunlight. So under the skin, you can convert sunlight mixed with various lipids and fats into this compound, which we call a vitamin, but is actually more like a pro-hormone or a form of a steroid. So it's closer to a steroid than it is to a vitamin. And I think our reactions to it, if we're calling it a steroid, would be very different. It's been

had fantastic PR for the last hundred years just because it's called a vitamin, wrongly. And so I understand now it's not a vitamin. I have no idea what a steroid is. So could you help me to understand what it does do? We've got to call it vitamin D. I'm not going to rename it now. Parahormone D. There you go. Parahormone D is key to many, many functions in the body. That's why

we evolved to be able to synthesize it. And as we moved out of Africa, our skin got lighter so that we could get more of sunlight in and convert it into vitamin D. So we know it's very important for our bodily function. And it's crucial for our immune health primarily. That seems to be the main driver of it, but it's involved in all kinds of reactions. Just like, in a way, the other vitamins are, it's not different in that. It's just coming at it from a different angle. So we know that it's involved in many immune reactions, and our response to the environment is fairly crucial. And when we

talk about immune reactions, we're talking about inflammation, we're talking about the response to allergies, response to aging and cancers. And it has a very general plan of action, as well as specific effects on things like bone health and growth. So that's where it sort of comes into its more specific roles in that you can't create bone properly if you don't have some vitamin D on board. You absolutely need it. It's like, I feel like quite a lot of things we end up talking about on the show is like involved in lots of different things. You can't live without it. Absolutely. But you're saying the key difference between this and generally the vitamins that we talk about is that generally those are

vitamins that the body can't create at all. So you've got to ingest them in like very low levels, but you've got to have it. Whereas here we can actually make it ourselves. So Federica, is sunlight the only way we can get vitamin D? So no, it's not. We can get it in food. I think what's important as well to note is that actually now we've discovered that, for example, vitamin K is made by gut microbes. So it's not the only vitamin that isn't made by some part of our body. But Tim's right in that it's the vitamin that our body is very well adapted to make plenty of for us if we just get enough sunlight exposure. We can also get it in food, but generally speaking, we can't get enough of it in food compared to what we need for our health.

So we do need to get some sunlight exposure onto our skin to create vitamin D. What's the recommended daily intake of vitamin D? And I'm sitting here feeling that I know I haven't got enough of it, that no one I know has got enough of it because I'm surrounded by all this advertising telling me that I need to take more. So Jonathan, this is really complicated actually, because we have receptors for vitamin D all over our body, every single tissue, right? And that causes a cascade of reactions, including different gene expressions. It's hard to even measure how much vitamin D we have in our bodies, let alone how much of it we're actually converting to other

things, because that depends on how many receptors you are. So it's not a simple answer. And it goes back to what Tim was saying. This is a parahormone. It's a bit like if I said, what's the recommended amount of estrogen that every woman should have? There isn't a recommended amount, but the UK and the US differ quite a lot in what they consider to be healthy amounts in the blood and what people should supplement through not food but supplementation and it's really interesting because when you look at the recommendations they clearly state that these recommended amounts to take as supplements excludes any exposure to sunlight and any food intake so already these recommendations are aiming at helping people who have very little sunlight exposure and maybe don't have the right foods in their diet to include vitamin D.

And these numbers are 28 nanograms in the US as the recommended blood level, whereas in the UK, we recommend 12 nanograms. And in the UK, we recommend 400 international units per day for adults. And for the US, we recommend 800 international units per day for adults. And for the US, we recommend 800 international units per day. So very different numbers, which we'll get to why that is or why we think that is because it's a very interesting story. As a supplement, just to make clear. That's exactly, excluding sunlight exposure and food. So it's interesting because in my career, I obviously started studying vitamin D as a rheumatologist in the late 1980s. And when I started, there weren't many labs measuring vitamin

D. And the only cases you saw were these rickets and osteomalacia. These are when the bones go bendy and soft. And you might remember those pictures from the 50s and 60s where many poor children had bow legs and stunted growth. And there's an adult form of this called osteomalacia. These were serious diseases, and people had no vitamin D to grow their bones at all. And slowly, the level of what was seen as the normal level of vitamin D in the blood rose from actually having quite minimal levels where you saw these diseases to every 10 years,

like doubling up to the point where many organizations around the world or in the US are claiming you need very high blood levels to be seen as having sufficient vitamin D. Now, as Federico explained, it's very difficult to know what that level is because you're actually trying to measure things in the cell, not actually directly from the blood. And I think that's being directed more by the vitamin D companies and the commercial pressures than from science. And many people who are experts in vitamin D agree with me that it's just been pushed up and up and up without really any scientific evidence to say that 28 nanograms

is better than 14 nanograms and that there isn't a universal amount. And it's confused by the fact that we did a very large twin study to show that the blood levels you have is not so much dictated by how much you eat or once you go in the sunshine but it has a genetic basis so about half of that difference between people is actually genetic so everyone has their own personal vitamin d blood level that suits them which makes it even less likely that you can sort of give everyone the same level across the world and say that's what they need so it's extremely problematic and i think it's been driven more by commercial concerns than by real clinical evidence and can i ask a bit more about the consequences of deficiency so i think you were taking this picture of what happened with children

with absolutely no vitamin D, which sounds pretty terrible. Are there levels of deficiency still below that? And like what percentage of people are classified that? And what happens to you if you're in this sort of low level of vitamin D, but not like the complete absence that you were sort of describing? So that's the difference between deficiency and insufficiency. And that's where the lines get a bit blurred. Because with deficiency, as Tim described, you see a real change in bone structure in children and in the quality of bone, even in adults. So it's quite easy to see and measure.

What you mean is they can fracture with very painful fractures that look really obvious on the x-ray and they don't heal up well. And so if you're in the US or in Western Europe, what fraction of people have that level of vitamin D deficiency? It's a tiny, tiny amount that have deficiency. Luckily, rickets is really rare. There is a strange increase in numbers in the UK and the US, but we think that's mostly related to lifestyle and diet actually, but really vanishingly rare to see somebody with rickets at osteomalacia. However, when you look at the reports, countries will report that there's between a 10% to 14% in the UK deficiency

and in the US it's up to 30%. Some other papers have suggested that deficiency and insufficiency might be as much as half of the population. But these are based on numbers from surveys and they are with these inflated numbers that we're expected to reach. And you see this across the randomized control trials as well, where some participants in the randomized control trials will go into vitamin D trials with very high blood levels already, and then they're given extra to reach even higher levels. So it's, I think when you look at clinical reports of

osteomalacia or rickets, they're still incredibly low, very rare. But sometimes the reporting of how many adults are missing vitamin D or lacking vitamin D in the US and UK can seem alarmingly high. But just to clarify, because I used to treat people with osteomalacia, which is the adult form of rickets. And you'd often see this in immigrant populations who are changing their diet, had come to a place where there's a lot of sunshine to no sunshine, and their diet wasn't adequate, and they may have been lacking it as children anyway. And so they would come with very painful muscles, aching in their body, very tired, and they'd have these rather weird fractures for little reason at all. So that's the classical picture of the adult form of rickets, which we call osteomalacia. And it tells you that's what the symptoms of real vitamin D deficiency are. They're painful joints,

painful muscles, and the consequences with these fractures. Everything else we're talking about is like theoretical risks or theoretical problems. This is where we get into this difficult territory. And Tim, can I ask you about the health consequences of what you're talking about, the theoretical deficiency? So you're saying like there's this people, it's really clear they're getting these awful fractures, but that's with the extreme deficiency. And then we're hearing there's maybe 30% of the population that's deficient. What are the symptoms? Depression, tiredness, all kinds of mental illness.

There were these conditions like fibromyalgia, which were supposed to be associated with it. Everything that couldn't be explained by medical science was, in the last several decades, been linked to vitamin D deficiency. And in general, if you take super healthy people and you compare them with generally unhealthy people, there will be a difference in their blood vitamin D levels. And the healthier people will have higher vitamin D on average.

It's a sort of marker of health. And I think this is why the whole literature is rather confused. But if you think about it, someone on a healthy diet who's going outdoors and doing sports and things is going to have a higher vitamin D level than someone who is unwell and sitting inside and on a poor diet. So this is where the whole literature has got very confused and people have associated the fact that it's a health marker with the fact that, oh, we just have to give you more of that health marker and you can be even better and healthy. That's really interesting. So it sounds

like everyone agrees you need some vitamin D or that's a huge problem. There's quite a lot of controversy about whether a large fraction of the population is really deficient and this is really causing them symptoms or whether actually it's a much smaller fraction who are truly having symptoms from lack of vitamin D. Yeah, well, it's not a controversy in my eyes, but yeah, that's... And it's not a controversy in your eyes because... Because I believe that you don't need that much vitamin D and everything above that, you're fine. I've seen so many patients,

for example, with extremely low levels, sort of nearly off the charts, including one who was a colleague of mine who was an expert in vitamin D and calcium. He came from Sri Lanka and he'd been walking around for years with virtually no levels and felt completely fine. So I think the idea that it's this amazing thing that is like a thermostat of our health and we just have to top it up every now and again is very misleading. But at the same time, I've seen vitamin D cure some of my patients. And if you give vitamin D to someone with these painful fractures, their pain goes away nearly immediately. It's this ground where I think the industry has made a disease

where none really existed. And Federica, I'd love to get your perspective. I think because it's such a marker of health, I can see how there's lots of studies that show how individuals who suffer with certain conditions, including depression, multiple sclerosis, Crohn's disease, cancer, they tend to have lower vitamin D levels. So I understand how, you know, when you have these patients, giving them vitamin D could be one of the tools that you use to help improve what's known to be a marker of health. And so I know what Tim is saying in terms of the deficiencies are pretty hardcore and easy to spot clinically, But there's this insufficiency range, which lends itself to giving your patient or your client an intervention that might be helpful. And Jonathan,

we've just spoken about the fact that vitamin D receptors are all over the body and they impact all tissues. And there's a lot we still don't understand about vitamin D. So from a public health perspective, there is little harm in recommending that certain patient groups take vitamin D to help them reach that healthy marker level that we feel would be good for them, basically. Now, it's true that the markers are so different between the UK and the US. I feel that the US has been conflated and inflated because of industry intervention, and there's been lots written about this but if we take the sort of medical cutoffs I think it can be very helpful to give people

vitamin D to get them above that critical deficiency line and it could be something that helps them without harming them and that's really important. How would someone know if they're low in vitamin D? There's a blood test you can have 25 hydroxy D which is one of the metabolites of vitamin D so as we sort of said earlier it's really hard to actually measure vitamin D status and this is the best proxy measure and so a proxy measure means that it gives us an idea of how your body is breaking this down but it doesn't necessarily tell us how it's being used or what effects it's having. So again, very hard to know how useful. And some countries and other places have an alternative test called the parathyroid hormone,

which goes up if you're deficient. And that might be a better way of seeing that. So they go in opposite directions. So if your body needs vitamin D, in a way your parathyroid hormone goes up and therefore it starts to get nutrients from the bone. And I feel this is something that I have been told about by doctors in both the US and the UK. So is this quite a typical sort of clinician's test? Absolutely, yes. But it's been a problem because we don't

know what the normal levels are. And that also goes for parathyroid hormone, it goes for these vitamin D levels. And so I think, you know, medicine likes to play safe. So what we've done every 10 years, just keep raising this level, the bar, so that half the population are now seen to be deficient, whereas it perhaps should be, you know, 1% of the population, you've now got 50% nervous and worried that they've got some deficiency or problem. So this is the risk of taking this route and treating it like, okay, let's give everyone this. It's all harmless. That'll be fine. And it's absolutely not the case. And I think by focusing on these things, you're then neglecting many other things you could be doing for their healthcare. You could be looking much more at their diet, you could be

looking at their lifestyle, their exercise levels, or some other disease that they've got. So at the moment, we're very focused on this as the cure-all, and the evidence simply doesn't back it up. So can we talk a bit about supplementation and the experience, I guess, that people are having? And then, you know, I think we're already exposing definitely a spread of you about what to do. And we said there's quite a big difference between, you know, the US and the UK, which is actually very surprising because it's been very unusual across these podcasts that we ever have that. And I think that itself is interesting. It sounds like you're saying like 30 to 50% of people might be low on this number. What happens when that's the case? Well, if you

see your family doctor and they do a blood screen for you and show you're below that level, they would probably prescribe a vitamin D supplement with or without calcium. And that, I think, is fairly common around the world, depending on each country's cutoff levels and what their lab is telling them, all of which are very different. And even in the world, depending on each country's cutoff levels and what their lab is telling them, all of which are very different. And even in the US, depending on whether you take, you know, the bone health colleges, the gynecologists, the cardiologists, you know, they've all got slightly different levels, interestingly. So there's no real consensus about where that level is. But once you've made that stand and you've taken it, then generally you'll be

prescribed a supplement and be told, oh, this should help X, Y, or Z, whether it's your tiredness, whether it's your depression, whether it's your muscle aches, or it's going to be a general preventive for fractures. And that's still commonly practiced, although we now have scores of trials showing that it doesn't work. I would love to discuss what does the science say? So presumably there have been real clinical trials to try and answer this question? So there's two types of study. There was the ones that led to this, which were the epidemiology studies, which compared 100 different diseases to controls. And as we discussed, they found vitamin D levels were generally lower in the disease group

than compared to the control group, for the reasons we've discussed. Virtually all likely be lifestyle and self-selection of people because of their disease. It's not before that, it's after they have the disease. These are called observational studies. They're a useful starting point in epidemiology, and that's how lung cancer and smoking came about. That's the starting point, but it doesn't prove anything because there are all these other factors, particularly with something that's involved in lifestyle,

diet, and general health. A disease could lure it. The fact that you're sick, you stay indoors. The fact you're sick, you're not eating well, all those three things can lower your vitamin D. So that's probably the explanation for why it was associated with a hundred different diseases all erroneously. Then you've got the clinical trials and they're seen as the gold standard of this. And I actually did one about 20 years ago in twins. We gave calcium and vitamin D to one twin and we gave dummy to the other one and measured their bone densities, et cetera, and found no differences. And we thought this is strange because everyone was saying this should be a miracle cure. And at the time, there were a few studies dating back to, I think, the late 80s when they did some big studies in France in nursing homes.

Yeah. And they basically randomized nursing homes to be given vitamin D supplements or not and found a difference in fracture within two years of doing this. And people said, oh, wow. And from that point, really, everyone was told vitamin D can prevent fractures and is really important in old age. But bit by bit, there have been another 20 studies or so, including a massive U.S. study called the VITAL trial, that have shown no difference at all in fracture rates. I will come in on that though and say that the study that was done in the old people's home was looking at people over the age of 65. The vital trial, the average age is about 50. So actually, when we look at the evidence, there is some suggestion that older people,

especially women that are in a care home setting, may benefit from vitamin D supplementation. So I think within these trials, there's subgroups of people who do seem to benefit, but they are the minority. And Tim was talking about family physician and prescribing, but actually the public health recommendation in the UK is that everyone supplements with vitamin D from October through March. That's 400 international units of 10 micrograms. So the question becomes whether

everyone's supplementing is helpful or whether we should really be focusing on the groups in the randomized controlled trials that did show an improvement in their outcomes. Yes, but a lot of people have discredited that very early French study. The guys who were running the study ended up having their own companies selling vitamin D. That doesn't help. And it was never been replicated. So there have been other subsequent studies in old people's home that haven't found the same effect. So I'm not saying we can prove definitely.

And yes, these are very high-risk individuals and very high risk of hip fractures in old age homes. They don't go out much. The diet is not be good. I think it's still reasonable to do that. But I think we have to be a bit cautious about how great the evidence is. Did you say there was a third type of study that you were going to talk about as well? Yes. There's another study based on genetics, which is called...

Very complicated, Jonathan. I'm sorry about this. It's called Mendelian randomization. Well, it's got a fantastic name. I've heard the name before, and I don't have any idea what it means. What is Mendelian randomization? Well, you might remember this monk, Gregor Mendel, who did this pea experiment. He probably faked a bit of the results. he basically sorted out the idea that you inherit these these genes from your parents and they get passed down and the sort of

they're mixed up and then they get separated so the idea is that once you've discovered the genes for something for say vitamin d and i actually led a study of this about 10 years ago showing that not only was vitamin D genetic, but that you could determine what genes controlled it. So there are about 10 gene variants that we've all got that can make your vitamin D level higher or lower. This is the thing you were saying before that actually amongst different people, like my wife and I might be making very different levels of vitamin D, even though we're eating the same food and we're having the same amount of sunlight.

Exactly. And it might be perfectly healthy for you to have lower levels than vitamin D, even though we're eating the same food and we're having the same amount of sunlight. Exactly. And it might be perfectly healthy for you to have lower levels than your wife because your genes have decided that's what they want to do. We're not sure. We don't know which way around it works. But you would expect that if you've got the genes for low vitamin D, then it doesn't matter what stage you are at life, you're going to have had lower vitamin D levels than your wife. So it's like doing a randomized trial lifelong because you can't change your genes. They can't be influenced by your disease. They can't be influenced by whether you live in Spain or Iceland.

It's the same. So this was supposed to show that people with these low vitamin D traits, these low vitamin D genes, these low vitamin D genes, should have higher fracture levels. And they've done this in over a million people now. And there's absolutely no difference. There's no difference whatsoever if your genes are making more vitamin D than someone else. Absolutely none. So if you combine that with the meta-analyses of all these randomized trials, really the evidence that vitamin D supplementation has any role in bone health once you're out of that rare deficiency range, it doesn't exist. And there's some evidence from about three trials where they gave quite high levels of vitamin D that you make

it worse. And actually there was one trial that showed that actually more than one trial that showed that if you have the vitamin D plus calcium in some populations older people can increase risk of cardiovascular disease so that's where the vitamin D calcium supplementation issue comes up and you know I'm always quite wary if people are taking large amounts of calcium supplements because again the thinking there is that it could help with your bone health well there's even less evidence that calcium supplements work compared to vitamin d and there's even better evidence that it's really harmful for you so i don't think anyone listening unless they've been given specific advice by their doctor should be taking calcium and supplementation.

Because there's quite a lot of evidence, both in animals and in humans, that it can lead to atherosclerosis, a sort of clogging up of the arteries. Because you think about getting calcium naturally from plants or dairy or whatever form it is, you're getting small, tiny amounts all the time, regularly, which your body's

used to. To take a big one gram tablet of this once a day that your body's got to deal with, we're not meant to do. And it's not surprising that it ends up in the wrong place. You are saying that unless a doctor has specifically prescribed calcium supplementation, Tim, you think people should not be taking it because you think it's not just that it's neutral, it's positively harmful and can hurt your health. Absolutely, and particularly your heart. And particularly your heart.

Because I think it's rather terrifying, right? Because you can't buy it at the store anywhere. It doesn't have great big labels on it saying warning. Have we known this forever or is this different from what we understood 20 or 30 years ago? We've known it for the last 10 years, but such is the difficulty of changing medical mindsets and the power of the supplement industry that really hasn't still got mainstream. And so most family doctors are still prescribing it, although many of the specialists now are not. People who suffer with osteoporosis or bone disease sometimes are prescribed both.

And the randomized control trials, even in the groups who have a higher chance of problems like osteoporosis, the trials clearly show that the vitamin D plus calcium combination is not helpful. And it's not helpful for the bones and actually could be dangerous for your heart. So it's interesting that it's very clear in the bones and actually could be dangerous for your heart. So it's interesting that it's very clear in the research, but as Tim said, people still take it. And I've seen it as well, where people come to me and they say,

this is what I'm taking. I'm like, let's not take the calcium. Hi, I love that you're listening to this. It means a lot to me and the whole team who put such a lot of hours into this podcast each week. We release this show for free without ads to help millions of people improve their health with cutting-edge science. In return, all I ask is that you help us on this mission. If you know someone who'd benefit from listening to this episode, please send them a link to this show. And if you haven't already, hit follow wherever you're listening right now.

Thank you, and on with this show. And if you haven't already, hit follow wherever you're listening right now. Thank you, and on with the show. And what about the vitamin D alone? So I think you're saying very clearly, like if a combination with calcium is like definitely out, is there any downside of taking these vitamin D supplements? You know, is there any risk? Can I take too much? Absolutely. We didn't think there was, but in the last 10 years, there have been several trials where they've given people larger than 400 units up to 5,000 units a day, and many people are self-medicating. And in these trials, they've shown that the group that were having, say, vitamin D by injections or large amounts by mouth had increased fractures

and increased falls. So the researchers in those trials have really changed their minds about it. So you can overdose on these. And increasingly in clinics, we're seeing people who are self-medicating from the internet. You can get very high-dose tablets from the internet, which seems very strange. And these are very, very dangerous because you do accumulate the vitamin D in your body. It doesn't just get peed out like some other B vitamins. So you will get more and more levels and that can cause real problems, nerve problems, muscle problems. And because it's called a vitamin, people think it's harmless. It's not just getting passed straight out if I don't need it? Correct. That's right. It does depend on the form you're taking it. But in general,

that's correct because it does build up and it is dangerous. So again, it comes back to this idea of taking a supplement in a chemical form is often different to, you know, you can't get too much from sunlight or from food i think that's it's more like a drug right like i could take paracetamol that's great it helps with my headache but i know that if have loads of their you know it could really hurt me or kill me and so you're saying that i should think about vitamin d a bit more like that yeah so when you go and buy tylenol you're not allowed to buy you 500 of those tablets, but you can buy unlimited amounts of vitamin D and self-medicate. And I think it's just wrong. And if it was called a steroid,

you wouldn't have this. It would be more controlled. And that's why our body is well set. I can go in the sun as much as I like, and I may have noticed I've been in the sun, but my vitamin D isn't going to keep going up. My body knows when I've got enough. We have a system for controlling it when it comes from food or sun. We don't have any system to control it when we're having it as a pharmaceutical. Everything we've talked about has really been around bone health and the impact on fractures. Is that the whole role of vitamin D? Because I feel like lots of people are taking it because they think it's going to help with their general health. And does that also mean that if

I'm not worried about fractures, then I can keep taking lots of it because I don't think that's a very big risk for me? No, there's so much more to the research and there's so much more to how we think vitamin D works. So we spoke at the beginning, Jonathan, about its role in immune system function. And I think that's where research has been more promising for the use of vitamin D, even as supplements. Because, for example, with groups of patients who have, for example, Crohn's disease, which is an inflammatory disease, we see that those individuals benefit from vitamin D supplementation in randomized control trials. They have a reduced risk of hospitalization and complications. Now, if we think about this as a steroid that helps immune system function in individuals who have complicated

inflammatory diseases, it makes sense that supplementing with vitamin D could help to mitigate some of these problems. Another group that has seen some good outcomes in the vital trial is patients who have cancer. Now, not to prevent cancer, but if you already have cancer, taking vitamin D could actually help to reduce mortality risk. Now, again, this is in a subset of patients, so patients who don't have obesity, whereas patients who do don't seem to benefit. And that probably comes back to how the vitamin D is stored in tissues. So again, try to understand how this works in our bodies is really important. And so where I stand is like there is exciting evidence that this could be

helpful in certain groups of people and really make a difference on the outcomes for those people. And so where does this leave the two of you on supplementation? I'm living in a northerly climb, which is dark all winter. And that is going to be true for quite a few of our listeners. And I think they're getting this message that you're just not going to get enough from the sunshine during the winter. So you should supplement. That is the outside. Should they be supplementing? And if so, how much? There is reams of evidence that getting outside all year round is helpful for our health for lots of reasons, not just vitamin D. Now, if you get outside all year round, including in the summer months, being mindful of your skin tone. So some people listening to this, like myself and definitely like Tim, can get outside and not wear a strong sunscreen and not get sunburned, right?

Other listeners listening know that if they go outside for more than five minutes, they will get sunburned. Sunburn is always a risk factor. But if you can go in the sun and enjoy 15 to 20 minutes outside without sunscreen, without getting burnt, so with no redness, then doing that every day is recommended. Remembering that we accumulate vitamin D means that if we get enough sunlight exposure in the months when there is sunlight, right, then we'll probably have enough to carry us through the winter months. But if you're somebody who can't get outside, if you're somebody who has perhaps a really sensitive skin tone and finds it difficult to go outside, or if you're somebody who already has compromised health, so maybe you're an older person living in a care home maybe you have Crohn's disease or maybe you've just been diagnosed with cancer then it may be worth speaking to your healthcare

professional and getting some vitamin D supplementation because it could be helpful but I will really again come back to this vitamin D toxicity I've seen vitamin D toxicity and it's really not fun there is a lot of influences online that are promoting very high levels of vitamin D. So the takeaway for me with vitamin D is if you're in one of these groups who could benefit, make sure you're getting the 400 international units in the UK, that's 10 micrograms in the US, they recommend up to 800 international units, which is 20 micrograms. But really, if you're taking 400 international units a day in one of these groups, you could see a benefit. So I don't completely disagree with that.

But I don't want to give the impression that everyone living in Northern Europe or parts of Northern America and Canada, you know, should be so dependent on vitamin D. I think we've evolved for tens of thousands of years to have the right conditions for our body. So we mustn't forget that. And if we have a diverse diet, then that's also going to help us. There are some conditions that, interestingly, I'm pretty convinced vitamin D can prevent. And one of those is something called multiple sclerosis, which many listeners may know about and my mom actually suffered from. And there's a link between people getting multiple sclerosis who live actually in northern hemisphere and in cold climates, and it gets less as you go

towards the equator. And this is one where this Mendelian randomization studies actually showed a difference in the likelihood of getting multiple sclerosis. So there are some rar know, my mother's got it, so I've got high risk, but I know my vitamin D level is high because I go in the sun, I have a good diet, so I'm not going to take supplements. But someone else might, if they're living in Alaska or living in Scotland, then it'd be quite reasonable in the winter months to take those supplements. But I think we've got to realize that, you know, I would say sunlight and food are a much better option for the vast majority of people. That's really clear. And we've gone on a little bit, but I do want to make sure I touch a bit these alternate ways of getting vitamin D. And so what are some of the foods that contain vitamin D? Well, most people know that it's contained in dairy products, which a lot of people are already eating.

So milk, cheese, keffirs, yogurts, et cetera. Then it's in oily fish and it's in mushrooms. And they're the key ones. And many people are not incorporating those in their diets. And that's why I think it's been quite interesting, this journey with Zoe and the nutrition program that we're seeing. We're getting people to eat these kind of foods, incorporate them more regularly into their diets. And that's just one example of how we can shift people's attitudes to foods so that they don't need supplements just by thinking intelligently about what they're eating.

If we think about it in proportions, I think up to about 30% of our requirements can come from the food we eat. It could really make a difference to that absolute minimum level of vitamin D you're getting compared to the sort of people living in these terrible conditions 100 years ago you're talking about. But compared to the sort of numbers

that the government is talking about, this now pushes you over to sunlight, is that right? As the much bigger thing that would drive your vitamin d levels being outside yeah that's interesting because a lot of place countries suffering for the most vitamin d deficiency are places like australia where they're now avoiding the sun and living in air-conditioned, you know, the inside for six months or more of the year. So as we're changing our environment away from nature, we are sort of developing some of these new problems.

It's about how we, you know, live with our evolution and our nature and everyone has to decide, you know, what those special examples are. That brings up a good point though, Jonathan, as well. If you're a person of color and you have darker skin and you live in these like cold climates then you are at higher risk because that sunlight that will actually penetrate your skin and create the vitamin d you won't get that in london right very rare or maybe like a couple of weeks a year so to tim's point we've evolved to adapt to our environment but now we're such an international community all over the world.

We have to be aware of what we need for ourselves and our backgrounds to make sure we don't lack. But also another important point, we talk about sunlight. I want to be super clear here that sunlight does not, there's no hack for sunlight. So having a sunbed so that you create vitamin D is not the way to do it, right?

There's this fine line between getting enough sunlight exposure, but not increasing your risk of it, right? There's this fine line between getting enough sunlight exposure but not increasing your risk of cancer, of skin cancer. Well, I was going to say, Federica, so both Tim and I are married dermatologists. So I happen to know that Tim created a storm in dermatology circles earlier this year because the idea of going out in the sun

without sort of factor 50 sunscreen is very controversial because quite reasonably, dermatologists spend a lot of time dealing with people with skin cancer and people who end up dying from skin cancer, right? So they see that. And therefore, there's been these very big campaigns across the States and Europe, Australia, about the extent to which whenever you go outside, you should make sure that you have a really high sunscreen. And I have to say that since I met Justine, I've wear out way more sunscreen than I had done before.

And you look so young, Jonathan. Well, thank you. And I am totally convinced that this is great for anti-aging. So I'm sold on that. But I think, Tim, you Tim, this conversation brings around this question about what the impact might be on vitamin D and health. And I think you had what I thought was a fairly nuanced position, but was interestingly very controversial. So will you tell us how you think about sun exposure and sunscreen, given this conversation of vitamin D?

It was triggered both by a research article I read, which was actually on mice, which normally I don't pay much attention to, but it was showing that how vitamin D was really important in helping the immune system deal with cancers. And the other thing was going in the tube and seeing posters by a UK skin charity, but basically sponsored by a sunscreen manufacturer, to say that we need sunscreen all year round in order to stay young and beautiful, and to protect us from the harmful rays of the sun. And the idea has permeated that we need 365 days of protection with a chemical, a pharmaceutical on our skin has permeated everywhere. So there are some schools in the US and the UK that won't let their children go unless

they've got sunscreen every day. And this is quite ridiculous in northern climes where you need every little bit of sunshine just to get enough vitamin D, you're not going to get any harmful radiation in that time. It's not going to make a significant difference to your aging. And dermatologists are seeing more and more problems of particularly young girls with major skin problems because they're applying so much chemicals to their face. And this just seemed to be totally driven by the sunscreen industry, who are going through charities and making it sound like it's all scientific. When I looked into it and when I asked melanoma experts like my wife,

there was obviously no evidence. And after about 2 million people had seen this tweet, and I got lots of nearly death threats for sort of insinuating that sunshine might be good, including from, you know, doctors and celebrities and various other people. It turns out the British Dermatological Association came out and said, actually, you know, he's right. There's no rationale for year-round use of this. And you need every bit of sunshine you can get in winter. So you're basically suggesting sunscreen in the summer when the sunshine is high and you've got this risk of burning all the rest of it. But actually, you know, if you're not lucky enough to be in Florida in the winter or whatever

it is, actually your view is you're better off not having the sunscreen because you're going to increase the vitamin D and that is much better than what you're saying. Not really real risks that they're worrying about to do with skin cancer and sparring. Correct, it's more likely to do harm than good. And definitely your skin health will probably be better if you don't have all these layers on every single day of your life.

Federica, too radical in your opinion? Well, tell that to women who wear lots of layers. But anyway, I think the main thing there though is we have to be mindful of sunburn again so i with children especially we know it's the evidence is really clear sunburn in childhood increases our risk your risk of melanoma later in life and so when it comes to protecting children's skin or again if you're somebody who's got extremely fair skin i think we know that you only need about 10 to 20 minutes of sunlight exposure

between 10am and 2pm to produce enough vitamin D. So you don't necessarily have to have prolonged exposure with no sunscreen. It's just about getting enough in every day. And I do agree with Tim 100% though that we don't need to be wearing SPF 50 throughout the winter months. It does just seem like a complete waste of money and a waste of a layer on our skin. But try buying a foundation cream for women that doesn't have SPF 30 or 50 in it. It's really hard. So women are not given the choice really, actually. That's the other thing that's quite interesting. I'd like to talk about COVID actually briefly and the immune system, because I that was a another big area with that when I was talking about vitamin D and preventing COVID you might remember that there was a huge

thing about taking it and this was absolutely crucial it was like 5,000 international units a day to prevent people were everything sold out as usual in this area in a bid to prevent it and we did our own study with Zoe looking at supplements and people, what they were taking. And interestingly, we looked about a million people and saw the severity of COVID. We saw a slight effect of vitamin D, but only in women.

This was a self-report observational study. The fact that it wasn't consistent in men, we said it was probably just selection bias and that women were buying it and they believed in it for the family. And the men were just, you know, being given it. And therefore it didn't help them. So it was a placebo effect.

But other studies have shown no benefit in COVID for vitamin D. And there were some big studies about injecting it for people with the disease that didn't show it unless they were very deficient. So people, again, in this sort of really deficient category will benefit from vitamin D. And it's, again, this nuanced argument that is really hard to convey to the public that if you're severely deficient in vitamin D, giving it can be life-saving. But if you've already got reasonable levels, having anything extra is really unlikely to help you at all and i think the same goes you know these studies of cancer and all the things related to immune system autoimmune

diseases etc so i think that's where we just need to think are you really deficient or not and only if you're really deficient should be really be really worried about this. Otherwise, I think sunshine and a diverse diet is going to be all you really need. And we should be worrying about other things and spending our money on other things. And that's why I think Zoe members who are getting all this education are in a much better position to think about the things that are really important in their health that they can make changes to, rather than just spending huge amounts of money on supplements that are proven not to work. Do you know someone who worries about their vitamin D levels, or maybe worries about their bones? Maybe they're unsure what a healthy vitamin intake really means.

Why not share this episode with them right now, and empower them to make better decisions based on the latest scientific advice? I'm sure they'll thank you. So it feels like you're basically saying for most people, they could save all the money they're spending on this vitamin D supplementation and spend it on something else that they're going to eat that is going to have a much bigger impact on their health. Is that? Spending more on real food, getting mushrooms, for example, that have been suntanning, the oily fish occasionally, just a more diverse diet and realizing that, yeah, just putting their arms in the sunshine and walking in the woods and the garden regularly is good for you. I think moving away from this miracle fix of the vitamin is really important

for these other aspects, this more holistic view of life. I mean, and I'm personally about this, about the vitamin D supplementation for the last three years, as Tim knows, but I'm coming away from this podcast pretty clear that as long as I'm able to get some sunshine, it's out the window, and I should be thinking about, you know, what am I doing really to feed the good bugs? Good man. You've got it, finally. And I think for those people who have caring responsibilities, maybe you have children, maybe you're helping with an elderly parent, having it in the home and maybe occasionally giving your child some or giving your elderly mother some isn't going to do them harm. But

there's other things that we can do for our health, which are going to have a much bigger impact and actually measurable improvements to our health. So if you've got some in your cupboard, you don't have to throw it in the bin. But definitely don't worry if you skip a few days, unless, as we said, you're in one of these minority groups of people who do have a specific condition that could benefit. Brilliant. Well, look, Federic and Tim, thank you very much. And I think for the listener, I hope that was fun because you can definitely see that there's agreement on what the studies are and what they say that you can have two scientists looking at this and still have some

spread of opinion. And we've had a lot of conversations like this over the last seven years. And I imagine we will have many more. I'm going to try and do a quick summary, if that's all right. So my biggest takeaway from all of this is do not take calcium supplements. Like if I think anyone listening, if there's one thing to take away is don't take calcium supplements unless they've been prescribed. And if you have friends and family who are taking calcium supplements, again, ask them like, has the doctor actually told you to take this? And if not, you should stop. So I think that's actually probably the most valuable thing I've taken away. Secondly, vitamin D is not even a vitamin. That does matter a bit because it means that,

for example, you really can overdose on vitamin D and end up with something that's toxic because you're saying if it was really a vitamin, you'd just sort of pee it out. But actually, it sort of builds up. And so that really should shift the way that I think about it and everyone else would think about it. And then the other bit is there's this huge gap between what the government is saying in terms of saying maybe 30% or more of the population is deficient in vitamin D and what you can really tell from people getting rickets or some of these other diseases, which is a tiny, tiny fraction. And so there is a big debate about really, are so many people deficient or is it actually just a product of the fact that we're all different

and our genes are different? And that the evidence on this has really shifted over the last 20 years where previously, you know, Tim was saying he also thought vitamin D was really good and would prescribe it because it was going to reduce fractures. And basically the data, the studies, one after another have been drip feeding and saying, actually, there is no evidence that if you take this vitamin D, it's going to reduce your risk of fractures, which was the original idea for taking it. And there is real evidence that you can overdose on it. So if you are taking really high levels of vitamin D, unless your doctor has told you

to do it, like stop again. And then I think critically, while there may be some groups, and Federica's pointing out some groups where supplementation could work. And interestingly, you're tending to talk about groups that might actually be living with some sort of disease. Maybe there's a role for people who are very old and in care homes. I think, Tim, you said that's also possible, but these are relatively small groups. What we should all be

doing is rethinking our attitude to the sun, particularly in the winter for people who are living in very northerly or southerly climates, or people who are living in a place where it's hot and they're putting on so much sunscreen like Australia or Florida all year round that they're getting none and that actually we need to rethink this balance between yes you want to avoid cancer you don't want to burn but on the other hand you do want to get some vitamin D from your skin and that for a lot of people that means that you could probably go out in the winter months without having to have sunscreen. And just to wrap up, I would say I have had a personal dispensation from my wife that

in the winter six months, I'm allowed to not wear sunscreen. And I think that her view has changed since I've known her. So I think what I see there, I think, Tim, is it's obviously a shift also in medical views from dermatologists and others as this evidence is changing, right? That the vitamin D is seen as something that matters if you can get it through something like the sun, whereas this supplementation has come under much more question. Yeah, and I think Tim's been saying this for a while, actually. I have to say, Jonathan, he's been very skeptical of vitamin D supplementation for general health and prevention of all disease. And the newer evidence is proving that Tim's approach has been right.

And I think quite satisfying for you, I guess, but it's important to always keep an open mind because the status quo on what recommendations are doesn't always hold. I don't want to puff up Tim's head anymore since, you know, we wouldn't want to recommend that. Could be another study next year that proves me wrong. So, you know, you're open to that. But, you know, and I open to, you know, if there's another way of giving vitamin D that actually works because it's so important in the body. It just so happens that the trials that have all been done so far, apart from saying multiple sclerosis and a few other rare diseases, you know, have not been effective. But I'm open to supplements

working, but let's look at the evidence clearly and come into it with our eyes open and not be driven by the industry into spending all our money on things that are proven not to work. And if I were going to wrap up, I'd just say, I think this reminds me of the conversations we have around food and nutrition all the time, where the latest science is very often completely different from what I was told 30 years ago is the right answer, that it's complex, you have to work it through. And it's part of the reason we spent so much time trying to figure out how we use sort of the membership in the app to guide people to understand what to change, because this is just vitamin D, right? Like, it's just one little part of how you think about improving your health. It is complex.

And I think what's interesting is just how many areas scientists are now saying, actually, you know what, the view that we had 30 years ago with a lot less data we've really changed a lot and that there has been an enormous amount of research that's going on around the world in so many of these areas I think you know Tim is generally saying well actually you know what this has really changed you know my views and our views about what we should do but I do think that though the science is complex I think the advice remains quite simple and Jonathan we obviously know this in the app and in the way we speak to our members but eating a whole food-based diet where you have a lot of plants on your plate and being active throughout the day preferably outside is quite simple in terms of the messaging so I think we mustn't lose sight of the fact that these are all things people can do and it's quite easy to make

that change obviously it's easier when you have the help of someone like Zoe to do it. Yeah, so it's a holistic approach. It's not about one little chemical. It's all about the thousands of chemicals, the whole complexity of our body that we need to embrace. And that's why this whole idea of diversity is absolutely crucial.

Brilliant. Thank you both very much. Thank you. Pleasure. I loved having Tim much. Thank you. Pleasure. I loved having Tim and Federica on the podcast today. I hope you learned something new and enjoyed watching them disagree a little bit. My biggest takeaway is that if possible,

we should try to get our vitamin D from natural sources. Now, if you listen to the show regularly, you probably already believe that you can transform your health with food. regularly, you probably already believe that you can transform your health with food. But there is only so much that you can learn from general advice on a weekly podcast. If you want to feel much better and be on track for more healthy years, you need something more. And that's why each day, more than 100,000 people rely on Zoe membership, our personalized nutrition program, to make smarter food choices so they can feel better in weeks and be on track for more healthy

years. So how does Zoe membership work? First, your at-home tests allow you to understand your body's responses to food and the good and the bad microbes that are in your gut. Then Zoe's app uses your test results to create your personalized program, helping you to build life-changing nutrition habits step by step. Your program includes recipes, meal plans, food scanning, and simple scores out of 100 for any meal. Regularly retesting your gut health lets you track your progress. I rely on Zoe's advice every day, and truly it has transformed how I feel. So, will you give Zoe a try? The first step is easy. Take our free quiz to find out what Zoe membership could do for you.

Simply go to zoe.com, where as a podcast listener, you can get 10% off using the code podcast. The Zoe Science and Nutrition podcast is not medical advice. And if you have any medical concerns, please consult your doctor. See you next time. Thank you.