Professor Tim Spector: I was wrong about Vitamin D & sunlight! The 7 health habits he's changed his mind about

0:00Welcome to Zoe Science and Nutrition, where world-leading scientists explain how their research can improve your health.

0:13Health advice never stands still. One year we cut fat, the next we fear sugar. We demonize seed oils, and then we defend them. The headlines move quickly, but inside the body, change unfolds slowly. Arteries clog over decades. Risk accumulates long before symptoms appear. Professor Tim Spector, one of the world's most cited scientists, has spent years studying how food and lifestyle shape these invisible processes. He challenged calorie counting when everyone else believed in it. He warned about ultra-processed food, while many nutrition scientists deny that there was even such a thing. And of course, he has led the world in understanding the central role of the microbiome in our health.

0:55But science does not freeze in time. New trials emerge. Larger datasets appear. Evidence deepens, or sometimes it reverses. This year, Tim has been examining his own health closely. He's reviewing new research. He's looking at his own test results. Today, Tim explains where he has changed his mind, where he hasn't, and how he decides where new evidence is strong enough to act on. He shares the seven new habits that he started in 2026, from supplements and new exercises, to sleep and oral health, and the reasoning behind each one. Because the challenge isn't keeping up with every new health claim on social media.

1:35It's knowing which ones deserve your attention and which ones you can safely ignore. By the end of this episode, you won't just have heard the changes that one of the world's top scientists had made in his life. You'll understand how to navigate shifting advice for yourself. Tim, thank you for joining me today. Great to be here. I don't really need to tell you the drill. We have a set of Q &A questions. The good news is you don't know what they are, but I do. Okay, far away. If I brush my teeth badly, could this impact my brain health? Definitely. Have you changed the way that you exercise this year?

2:12I have a little bit, yes. Is folic acid only important for women? No, as I've recently discovered. Is it true that you now have rippling biceps thanks to your new workout routine? You can see for yourself, Jonathan. Yeah, I mean, you know, I've added at least 1 % to my muscle mass. All right. And then finally, what developing area of science are you most excited about in 2026? I'm really into the brain and the gut-brain connection. I just think it's absolutely fascinating. And a lot of that has come out of the Zoe studies that have pointed in that direction, areas we didn't think about when we started Zoe.

2:58I'd like to start, before we get into the specific things that you've changed in the last year, maybe step back a little bit and say, what is it about nutrition science that means that we don't just know all the answers. Because I think I was generally brought up to believe, well, science has figured all this stuff out. And I certainly was under the impression, you know, 40 years ago that the government knew exactly what we should eat. There's a certain naivety about public perception of these things, in a way, because governments are forced to have guidelines. And guidelines tend to be very black and white.

3:38And there isn't really room for nuance when people are giving out a leaflet or something. And so this then leads to a mentality that we have to follow the guidelines and that the guidelines must be correct. Otherwise, all our foundations are going to crumble. And that's why we've taken so long to get to this point to realize that most of the guidelines were wrong and that actually the science has changed. And can you give an example of where scientific opinion has changed in a big way in your lifetime? In the nutrition space, I was brought up to think that fat was really bad for you. As a junior doctor, I was telling my patients, avoid fats, have starchy foods, things like rice, pasta, potatoes.

4:23They're the stuff to have that's really good for you. And they were, course in the guidelines. Nobody really questioned them, just kept saying it, and no research was done to prove the opposite. And it took ages until this has been reversed. And now most countries, although this country is lagging behind in the UK, but even in the US, they've now switched the concept of fat being bad to saying, actually, many fats are good for you. So that's probably the classic one where we made a 180 degree switch just in a few years, although it seems to have taken much longer than it should have done. And in that case, what I feel is from just talking to lots of scientists that this is a process of lots and lots of different scientists doing lots of different studies, reaching a point where there seemed to be quite a lot of scientific consensus about this for a long time, and then actually being very slow to change government guidelines and therefore public opinion?

5:23Yes, exactly right. The evidence became overwhelming about 10 years ago. And I remember going to some early nutrition conferences and for the first time hearing respected epidemiology colleagues who are generally the most conservative group of doctors saying, yes, we believe this fat idea is completely wrong and the evidence is now overwhelming. And it's taken sort of 10 years from that point to starting to get changes in guidelines. It's incredibly slow because people feel that things like dietary guidelines have such knock-on effects on the industry and changing formulation and changing commercial products that it's not something that should be rushed or just changed.

6:10And so this is why nutrition is different to other fields of science because it has this big industry over it and they're lobbying to make sure that nothing happens fast. And so is this different if you were working in cancer or heart disease and your work was only going to doctors to change their advice rather than actually just going to everybody to change what they eat? Would it be easier to sort of change the advice and make sure the advice was more up to date? Yes, in theory, but doctors just like many other professions, are really also set in their ways, and they don't like to change. Really?

6:48Yes. It's hard to believe, isn't it, Jonathan? We're a stubborn lot, and once you get into a nice way of doing something or treating people, and if you believe it, it's quite hard to change your mind on it. And the classic story was surgeons cutting the vagus nerve for ulcers, and it took 20 years to convince doctors to stop doing this so-called vagotomy operation because they enjoyed doing it. You know, surgeons loved this operation, although it turned out to be completely useless and used antibiotics instead. So even in medicine, it can take a long time to shift patterns and behaviors, but nutrition is even worse than most of these branches.

7:30So I think that helps to understand why there's this delay between maybe the science and what we all sort of understand. I'd love to go more personal now. How do you decide when a new scientific finding is worth incorporating into your actual lifestyle? That's a really hard question. I'm generally skeptical of any new finding that comes out of the blue. So if I see something, as we increasingly do on social media, some new trend coming out, the average influencer on social media, isn't a scientist. They don't really know how to rank the different levels of evidence. So I take various levels of evidence.

8:12I generally ignore stuff that's done in test tubes. Just on test tubes, we added this magic CMOS to cancer cells and it killed them all. I ignore that. It's just a pure example. And it's CMOS to mice and it stopped them cancers growing. slightly interesting but nine times out of ten completely irrelevant for humans and then some small study where they did a pilot study and they gave CMOS to people with cancer and improved some of their outcomes yeah okay we're starting to get interesting then you do a randomized study of CMOS versus non-CMOS and people with cancer and you get a survival advantage now I'm interested and I'm even more interested if you have a couple of studies and you put them together in a meta-analysis.

9:00So then once I've got this randomized control study, I'd say, okay, I'm going to look at taking CMOS. Am I going to put CMOS in my muesli every morning on my breakfast bowl? So it's a journey, but it means you do have to have a bit of a scientific brain to think of it in those terms, because the average internet influence is just going to look at any of this data and see them all as the same. And yet one is a thousand times more powerful than the other. And I seem to remember you telling me in one of our podcasts that there were some big studies, I think to do with breaking your bones, which really changed, for example, your mind about something that you'd been quite convinced about in science before, but I don't remember any of the details.

9:43Can you remind me? Yes, we were talking about vitamin D and how the early studies of vitamin D showed that it worked, that it had really important effects on bone turnover, bone biomarkers, and everybody worried about osteoporosis trying to prevent it should be on vitamin D medication. It was only when they started doing really big studies with good placebo groups followed for a long time, they found that the fracture rates in the two groups were no different at all. Because they'd been using in the past, a small numbers and like surrogate markers. These are like chemicals that the bones produce to show they're healthier or whatever, what we call intermediate biomarkers.

10:27But when it actually got to the big studies with fractures, actually there was no difference. People didn't believe the first negative study. They didn't believe the second one. But by the time they got to the third or the 10th, they did believe it. And that's now why osteoporosis experts know that vitamin D is not useful for the vast majority of people in preventing fractures. I was fooled by vitamin D, and I was a big promoter of vitamin D back in the day for osteoporosis. And it's still being used because most doctors haven't changed their practice. And so does a good scientist change his mind?

11:03A good scientist should change their mind because they should be always looking for a reason to contradict their current theory. You know, what evidence is there that's going to make what I think not true? I think that's really interesting. One thing I'm struck is certainly whenever you have two scientists in a room, and sometimes we have like 10 scientists in a room, they all argue with each other all the time. But the other thing I really do notice is that skepticism is also something they bring to their own work, and that sometimes proving that something is wrong is as exciting as not. Absolutely.

11:35I think scientists generally will be humble because they realize, you know, we're on a learning curve and that all scientists have made mistakes in their lives, as have all doctors. And it's realizing that and not just carrying on regardless, because I've said it five years ago and I keep shouting, it's got to be true. I would like to talk now about the things that you're changing, but maybe actually let's start with what you haven't changed in 2026. I know you've looked at all of this again and thought quite hard, but I'd like to start actually with what are the principles that you still have a lot of conviction about?

12:12Well, I'm still very convinced more than ever that the gut microbiome is crucial for our overall health. And if we have a healthy gut microbiome, pretty much everything else follows. And the evidence that we've been seeing continually just keeps to enhance that view. And was there anything important in terms of the science last year that sort of reinforced that view for you? Things like food quality are increasingly getting noticed as causes of our mental health and our physical health. That wasn't the case five years ago. And if you're talking about food quality, obviously, which organ does that impact more than anything?

12:49It's the gut microbes. There's also been a lot of really interesting immunology work that got a real boost after COVID. basic level understanding how the immune system is interacting with the gut microbes is revealing just how important it is to our biology. So, you know, it's across all sectors that we're learning this, plus our own Zoe studies that just keep showing that when you can improve people's gut microbes, you can improve so many aspects of our health, both short-term and long-term, and in the brain and in the gut. And you haven't mentioned so far ultra-processed foods? I haven't changed my mind on ultra-processed foods at all.

13:30And I think the evidence is getting clearer that they're the most important public health danger out there for the population. So I think they've overtaken smoking as the number one enemy we should be dealing with. The evidence is building, but we haven't had good definitions of it up to this point, and we've had too broad a description of what ultra-processed foods. So I'm really happy to have been helping with the ZOE redefinition of ultra-processed foods in these medium, high, and low categories of risk. But that is showing us how important understanding the food is. Around the world, this momentum is gathering a pace.

14:11And I think the next phase is to really define better what the harmful foods are and not lump it all together. We'll get much better results. so I'm pleased to hear that in the last year you haven't abandoned your belief in the gut health revolution because I think I'd be out of a job so that's that's good I'd like now to talk about the things where you have changed your mind and you gave me a list of seven things and the first thing that you said is that you've changed your mind about oral health so can you tell me what's so important about having clean teeth

14:48Tim Spector:another notification something else to add to the to-do list is it work is it life admin or maybe another email from your boss your heart rate might be quickening at the thought after all life is full of little moments that add to our mental load if you're feeling wired tired irritable or on edge that's your hormones responding to everyday stresses they're trying to tell you something and your diet could be part of the solution. Your gut is a hormone factory producing and responding to all the hormones that affect your hunger, mood, energy levels, and stress responses. Feeding it the right foods is a crucial step to supporting those systems.

15:29Tim Spector:That's why gut health experts Zoe and reproductive health pioneers Hertility have teamed up to create a free guide grounded in science to help you decode what your hormones are trying to tell you. You'll find out how stress responses can impact your body and how diet influences hormones, metabolism, and mood. You'll also find delicious recipes that support these systems. Learn more about your hormones today and download the free guide at zoe.com forward slash fertility or click the link in the episode description. I always knew that cleaning your teeth was important, stop falling apart and getting gum disease and your teeth falling out.

16:12and there was always a story about if you didn't brush them properly you'd get more heart attacks because there was certain microbes something called strep mutans that also had this potential effect on your heart but the last year or so i've been diving into this more and there's actually some good studies showing that your risk of dementia can be reduced by something like 20 to 40 percent just by cleaning your teeth optimally not just cleaning your teeth but cleaning teeth optimally and discovered this means flossing or using a pick. It was only when I started doing this and I started seeing I was getting bleeding, there were a few areas right at the back, really hard to reach, used to bleed when I just do them.

16:55I didn't think much of it. And it realized, well, you just got to keep going until you don't get bleeding. That means that you don't have inflammation. That means you're doing something really positive for your health and reducing your risk of future early dementia and heart disease. Can you explain how like flossing every day can have an effect on something that's not in my mouth, but it's in my heart or in my brain? Yes, it all comes back to our friends' microbes, microbiome. Just as in our gut and our colon, we've got these microbes in our mouth, in our saliva, they're there all the time and they have their own community.

17:33And essentially what you're doing, if you've got bits of food that are stuck in your gums and are very hard to reach places, this feeds these bad bacteria in your mouth, and they are pro-inflammatory. So they often send out these signals to our immune system to say, things aren't great. So they're just heightening the level of stress in the same way as if you're eating lots of junk food in your gut. Those signals will go to the immune system. And we now know, again, only very recently that the immune system communicates with the brain. We have immune cells in our brain recently discovered. And this seems to be a mechanism that your brain thinks it's under stress because it's getting these signals.

18:20It thinks it's like fighting infections all the time. And that seems to prematurely age it. So yeah, it's really cool to realize how much of your body is connected, things that we had no idea about before. It seemed crazy if you went someone 10 years ago to say this. And are you now flossing once a day, twice a day, 10 times a day? I will do it once a day unless I've got a problem, in which case I'll do it twice a day. I use these special picks now. Brilliant. Let me go on to the second one. So I understand that you did a scan in your body for microplastics. Is that right? I had this state-of-the-art dementia screening test, including all kinds of blood tests, scans that would be used for me to take action to delay or prevent dementia because I have a higher risk of dementia because of my mother having vascular dementia.

19:16And as part of this extensive all-day testing, I had this blood test done in the Netherlands for microplastics, and it showed I had above average levels. And this was a shock to me. I thought, why is that? And it turns out that some of them were in my particles that probably came from my lungs and others through the food you're eating. So you can get them from all kinds of places. You are saying that there were tiny little bits of plastic floating around in your blood. And so they just literally took like a blood test like normal. And here they're actually measuring plastic in it and they found a lot.

19:56That's correct. Yes. Essentially, it's like a plastic assay in your blood. And just the fact they're able to record any is slightly worrying. I think you'd agree. Yes, detectable will be bad enough. And then you say, well, actually, you're above average, that was even worse. So I did start researching that and thinking, well, yes, it is associated with people who have dementia, end up, you look in their brains, you can see some microplastics. It's associated with various cancers, all associated. There isn't hard evidence as such as we've been describing, but it's become added to that list of things that want to avoid, like pesticides or antibiotics or all these things that we'd rather do without.

20:40It just adds to this stress of life, another thing I've got to worry about. So I said, what could I do easily to do this? And so they said, well, move out of London was one, which isn't quite so easy to do. But I could spend more time on the beach, I think, and in Spain, Jonathan, I'll show you the proof of that. The other was maybe reduce plastic packaging in your food. i don't have very much anyway because i don't have things like ready meals but it made me you know always be more determined to use my zoe metal water bottle rather than the plastic one and try not to use glass rather than plastic and i even changed my toothpaste i realized that most of the toothpastes we use have not only lots of additives but a lot of them have microplastics in them as do a lot of shampoos so going to more natural ones and i've i use a natural toothpaste now that's made with fennel, for example.

21:33So yeah, I'm keeping my eye on it. I know the science isn't perfect, but if there's some easy things, then I'm happy to do that. I feel like this is very new and I'm sort of trying to ignore it because I don't want another thing to worry about. No, for the anxious, I wouldn't do it, you know, but I'm trying to do these experiments for other people in a way. So I take the stress. Thank you for doing that, Tim. Well, let's move on to the third one, omega-3. And I know that's a topic that's hotly debated in nutrition circles in terms of like the value of taking that as a supplement rather than just something that's within a food.

22:12What did your tests tell you about that? And what have you taken away? So my tests showed me that I had relatively low levels of omega-3 in my blood and also slightly high levels of omega-6. which is another fatty acid. And there used to be this idea that the ratio of the two was really important. You should cut out omega-6s. That turns out to be rubbish. We've reversed our view on that in the last five years. But omega-3 still remains important. But absolute levels aren't that interesting, according to the latest studies. But what is interesting is something called the omega-3 index, where you look at the amount of the important omega-3s in your blood cells.

22:58And there's something called EPA and DPA, which are the subtypes. And I was pretty low on those. So I was advised in this clinic to go on supplements. They said, go and take an expensive supplement. This is what you do. I said, I'm not very keen on that. Although the studies have shown that people with low levels do benefit from supplements in terms of heart disease. People average levels don't, but people low levels do. I said, I'm going to try and eat more oily fish. And so the last year, I've been making sure that every week I'm getting some anchovies and some sardines and some salmon in my diet, particularly easy when I spend time in Spain eating lots of anchovies.

23:45And I do love them. And I retested myself and my levels are now above average without having to take an omega-3 supplement. And that's because the fish itself contains those healthy omega-3s you were talking about? They do. That's right. Because they eat little planktons and things that do produce these plant products. So yes, they're a very good source. And I think it just shows you that you don't have to always reach for a supplement when the food could actually be a better supplement. Because not only are you getting the goodness from those particular fatty acids that we know about, but there's lots of other stuff that we don't yet know about that can be really beneficial.

24:26And they're really tasty. And that's why in my new cookbook, little plug here, Jonathan, I've got lots of anchovy and sardine recipes in there. So because I realized that plants are great, but every now and again, we need to spice them up. And just to clarify for anyone listening, this is a new cookbook you haven't actually released yet. So if anyone's feeling, I mean, why don't I know about that? Actually, you're working on it. It doesn't exist. I've been working on it and working on recipes. And I'm always trying to work out ways to put things like, you know, mackerel, sardines and anchovies into those recipes because we need to eat more of them.

24:59So you mentioned something about omega-3 index, that that was the thing that was low that triggered your concern. Is that like a standard test that I get if I get like a standard blood test? How would someone listening who wants to know about this for themselves solve that? It's fairly standard in the United States. It's not standard in the UK. So most GPs wouldn't be able to easily get people to test it. And I think it just shows a slight mismatch between the latest nutritional science and what the NHS, for example, is able to offer. And is the omega-3 index something different than just your omega-3 levels?

25:40I'm sorry, I'm still struggling to follow that. Yes. So in the past, people have looked at the ratio of omega-3 to omega-6. And the old idea was omega-3 was good, omega-6 was bad. And therefore, you wanted a high ratio. We now know that you want both to be high, omega-6 and omega-3. So that whole ratio idea has really gone out the window. and this new test really just looks at the amount of blood cells in your body that have sufficient levels of these really key omega-3s because omega-3 is a family there's quite a lot of them so we're just focusing on the the two important ones that's really what we should be looking at so this is now the gold standard in clinical research and it's just taken it's going to take a while to come to some bits the more conservative of medical world what would you say to anyone listening who's a vegan or really hates fish who is thinking, oh, I think I'd like to be able to increase my level of these healthy omega-3s?

26:45If they're already on a pretty healthy vegan diet and they're taking all the nuts and seeds and other sources of all the plants that contain these as well, I would say, yeah, get tested. And in those cases, if you're low, take a supplement. But randomly, some people will have naturally high levels, some people have low levels. It's not like everybody needs it. I think the evidence now is if you are low, it's probably worth taking their supplements. But a lot of people like me can get by just by upping their real food intake. And is your belief that if I'm thinking about this and saying, well, why not just pop an omega-3 tablet, right?

27:27People are always trying to sell me that. Is that just as good as the oily fish that you're talking about? We don't know is the honest answer. But generally, my belief is that if there's a food alternative, it tends to be better because it's got all kinds of other benefits to go with it that we haven't yet been able to uncover. Let's move on to number four. And we're still on nutrients and supplements because we're now going on to vitamin B12, about which I know absolutely nothing. So what is it and where does it come from? Well, it's one of the essential B vitamins humans, and although our body does produce some of it, our microbes produce some of it, we end up eliminating it.