ZOE Science & Nutrition - Most replayed moment: Do you really need vitamin supplements? | David Seres

Episode Date: August 4, 2026

Today we’re talking about vitamins. Walk into any pharmacy or supermarket and you’ll find a shelf stacked with brightly coloured jars promising better immunity, stronger bones and sharper minds. Of course, I’m talking about vitamin supplements. But despite looking like medical products, supplements aren’t held to the same rigorous testing standards as medicines. So how much of what they promise is actually backed by science? I’m joined by Dr. David Seres to help cut through the confusion and uncover what the science really says about vitamin C, vitamin D, and even the mysterious multivitamins. 🌱 Try our science-backed and tasty wholefood supplement Daily30 Get our brand-new app and Gut Health Test designed by world-leading gut health and nutrition scientists to build healthy eating habits 👉 Join ZOE Follow ZOE on Instagram. 📚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 Ferment by Prof. Tim Spector Good Mood Food (preorder) by Prof. Tim Spector Free resources from ZOE The Hormone Harmony Guide: Tuning Your Body’s Internal Orchestra Eating for Better Brain Health: Your brain-gut blueprint How to eat in 2026 - Discover ZOE’s 8 nutrition principles for long-term health Live Healthier: Top 10 Tips From ZOE Science & Nutrition Gut Guide - For a Healthier Microbiome in Weeks  Better Breakfast Guide Have feedback or a topic you'd like us to cover? Let us know here. Episode transcripts are available here.

Hello and welcome to Zoe Recap, where each week we find the best bits from one of our podcast episodes to help you improve your health. Walk into any pharmacy or supermarket and you'll find a shelf stacked with brightly coloured jars, promising better immunity, stronger bones and sharper minds. Of course, I'm talking about vitamin supplements. But despite looking like medical products, supplements aren't held to the same rigorous testing standards as medicines. So how much of what they promise is actually backed by science? I'm joined by Dr. David's series to help cut through the confusion and uncover what the science really says about vitamin C, vitamin D, and even the mysterious multivitamin. The history of vitamins is miraculous because there were different deficiencies in different populations in the world.

Iodine included, which would cause goiter and cretanism in children. vitamin D, as I mentioned, which caused rickets, vitamin C and sailors, et cetera. And each one of these was an enormous public health boon. I think that ever since then, we've been waiting for the next big, huge discovery around vitamins. And I think there aren't any left that we are aware of. Why do you think that the promise of vitamins has become so attractive for people who view themselves as healthy and who are not suffering from, you know, a deficiency that they're aware of or a doctor has told them they have? There's a general feeling in being human that one would like to control one's destiny. And health is this mysterious black box that if you are able to do

something now that will give you extended health and longevity, that's very attractive to be able to do that. And vitamins have been held out as this without good proof. But nonetheless, the ability to market them in the way that they're marketed, suggestive of health benefits, has fueled this. So when did they move from being this sort of niche thing to treat a particular disease to sort of widespread usage here in the States? I think it was probably a gradual sort of of thing. I know that in the 90s, a law was passed to deregulate the industry, but at the time, there was already enough money in the industry to have made large donations to political campaigns and so forth in order to promote the passage of this law called the Dietary Supplement Health

and Education Act of 1995, and D.S.H.E.A. or D. Shea, as some people call it. And the primary promoters got people to believe that this was nutrition and it was nourishing. And people also believed that the FDA was trying to regulate these substances when in fact no such effort was ongoing. And Mel Gibson was hired to do a commercial in which he is in his home, in his kitchen, in his bathrobe, surprised by a SWAT team arresting him because he's got vitamins. and he called for people to write to Congress. And that advertising campaign got more letters written to Congress than the entire Vietnam War.

Wow. It was very successful. So the ad was saying that I was going to have my vitamin C taken away. Yes. What was this legislation going to do? So this legislation essentially deregulates anything brought to the market that's called a dietary supplement. And by that, it takes away the ability for the U.S. Food and Drug Administration to regulate these substances and left specific ways in which the supplements were allowed to advertise suggestively.

So it's actually written into this that you can say that this stuff supports heart health or supports brain health without really any. direct evidence of it. And so they are allowed to make these health claims. Is that different from what would happen if you were a drug or if you were something else in terms of the claims you can make? Couldn't be more different. So a drunk company has to undergo a series of randomized control trials where people are randomly assigned to either the drug or a standard treatment or a placebo. and studied over time to determine whether or not the product does what it's supposed to do. And then that research has to pass muster with the FDA in order to be allowed to be sold as a medication or a drug. Dietary supplements are treated as if they were a completely different thing, where they are nutrients, so therefore they must be safe.

Thus, we don't want to deprive people of the ability to access them. And so they're available without any science necessary, without any proof of benefit necessary, and frankly, without any safety testing, although there is some accountability if something is dangerous. And so I'm guessing you're going to tell me that most people selling supplements do not do randomize trials of their supplement before they sell it? That's correct. Is it quite common, nonetheless, to do randomized trials for your supplement? It's actually fairly common to find randomized trials done, but usually it's by scientists. It may sometimes be supported by the industry, but the results of most of those studies have

failed to show benefit in the general healthy population for any of these supplements. Many supplements now have many different things in them, don't they? They're not just a vitamin. There's lots of different things. What's the difference between the randomized trial you're describing and saying, this is based on science and I've got papers against these ingredients? Sure. Because that sounds good.

Well, it does, and that's how it's easily used to sell. But you're corrupting the science to say that because let me explain it a little bit differently. There's a lot of data, and a lot of data is observational and showing these correlations. versus doing good randomized trials which lead to better conclusions around cause and effect. And what's also confusing is that, yes, okay, maybe it is based on science, but at what level is it science in a petri dish, or is it real actual science in real people, or even in animals, to show a health benefit from giving more of a substance?

So we've talked a lot of, I guess, about there have been issues around claims around supplements. I guess it's also true that one of the reasons that there's mistrust around sciences that scientists can also make mistakes, right? And they can change their mind and say that we said something in the past and now we said something now. And I think that that can cause a lot of, like, lots of trust amongst the public. I'm glad you raised this because it's one of the things that I think we're suffering from as a society to a great extent, to the point where being an end,

expert immediately makes you suspect, you know, that people think that you're just in it for the money or you're in cahoots with the drug companies or whatever. I think we got there by not caring enough about how we message our recommendations and the strength of the evidence on which the recommendations are based. When I say evidence and when somebody says evidence-based medicine, What they're really saying is that the quality of the data comes from a variety of levels of evidence where the highest level of evidence is randomized controlled trials. But the lowest evidence of just a case reporter or two could influence guidelines on which we base our medical practice or our dietary practices, et cetera.

Given all of this, what really should be the advice? And I'd love to start with the vitamins and talk about what should we all be taking. So what we should be taking is the time to make sure we have a relatively balanced diet if we have the luxury and the ability to afford it. And really, in my not very humble opinion, that is reliably eating food that looks more like it looked when it either was harvested or alive, swimming in the ocean, et cetera. So less processed, more sort of healthy and fresh, but that's easier said than done. And for people who are unable to access that and to do the best they can with that. As far as taking supplements is concerned, unless you have an identified risk or deficiency that your doctor has recommended that you take a supplement, there is really no benefit

to any of these with a couple of minor exceptions. And so for the general healthy population, the recommendation is don't waste your money and that what you're doing may in fact have risk that has not. not been identified because these have not been studied properly in long-term studies, such as I've mentioned with the vitamin E and selenium. It's a very powerful statement. I'd love to run through a few specific vitamins, so that people, I think, will say, yeah, yeah, yeah, yeah, but I know I need to take vitamin C because everyone knows that that's

really good for you. Come on, David. Surely that's an exception, isn't it? No. The studies in vitamin C have shown really no salutary benefit for, again, for healthy people who don't have a deficiency. With one minor exception, and that is in performance athletes, a couple of studies have shown that intense skiers and marathon runners had fewer colds if they took vitamin C, which is a thorn in my side, but the data is the data, and those were randomized

trials. So if you are in one of those groups and want to decrease the frequency of common cold, then perhaps vitamin C is something that you should consider, but at much lower doses than what are usually prescribed. And if I'm going to the gym a few times a week, don't I get to count like... Yeah, no. Okay. So you think really of no benefit? Really of no benefit.

What about vitamin D? Oh, boy. So vitamin D is a real headache for those of us who want to adhere to science on this. The story of vitamin D is actually kind of interesting, and that some years ago, a laboratory arbitrarily decided to label a certain range of vitamin D level as insufficient, based on very weak evidence. But they labeled it insufficient. So now all of a sudden, 50% of the population has vitamin D insufficiency.

And it created a billions of dollar industry in vitamin D testing. So that's piece number one. In the randomized control trials of the general population, vitamin D has not shown to have. much benefit. There have been some studies in older folks that showed maybe a slight decrease in the incidence of falls, but really not anything that's enough of a bang for your buck that I would recommend taking it. And of course, all of these have the potential for side effects and deleterious effects. So just to confirm, David, you are not taking vitamin D. I am not taking

vitamin D. And you think that at least for like the healthy population again, even if the lab test says that they're insufficient in vitamin D that you don't need to go and take this? Right. Now, this is debated hotly in the very lowest of those levels as to whether or not this really constitutes a deficiency or not. But without really good study, I really can't support that. When it's just a matter of opinion, people like to butt heads. When there's good, strong evidence, there's no fight. Is there any harm from taking megadoses of vitamin D? Yes.

Vitamin D at high doses can be very toxic. There are real potentially even deadly consequences. So I think, again, particularly for people who might not have heard anyone talking about vitamins on previous podcast, I think we'll be really shocked because I think they're generally presented as like something with no downside. Sure. Why not take it? It's sort of like insurance. You can't harm yourself.

After all, they sell it. And it looks just like the things you get as medicines and we know it's all, that's all supposed to be safe. So when could it be dangerous? Vitamin D helps regulate your calcium uptake from the intestine. And if you save too much calcium, you can put. deposits down in different tissues, the kidneys, the coronary arteries, and so forth. And I should be very careful to say that there are some studies that associate the use of calcium supplementation with an increased incidence of coronary disease, but that's not a

randomized trial, and it's not a cause and effect relationship proven. But it worries me enough that without any good proof of benefit and with the potential for harm, this is just one example of how it might be harmful that I would shy away from taking it. There is some suggestive evidence that people who take multivitamins may have a decrease incidence of dementia and some other things, but it's still very weak. And given the frequency over my career with which I have been surprised by the harmful effect of something, I really just can't get behind the idea of wholesale supplementation simply because you're over a certain age. And is that because you're cautious that potentially were like taking in these individual

chemicals like more than we would do through our natural food and therefore it potentially has a harmful effect rather than it just being a waste of money? That would be, well, both. And that would be one of many different possible reasons. But as I said, biology is complicated and we don't know until we have really good studies done, and it's never quite made sense to me that people don't think of vitamins taken for health benefit in the same way they would think about medications. If you're taking them for salutary health benefit, why would you not want to make sure that they'd been properly tested?

And the answer, I think, goes back to people wanting control of their health outcomes, not trusting the experts, and so forth. And I understand that, but I wish we, could get people to think about this in a different way.