Most replayed moment: Do you really need vitamin supplements? | David Seres

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.

• 0:01Speaker 00

  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 Seres to help cut through the confusion and uncover what the science really says about vitamin C, vitamin D, and even the mysterious multivitamin.

• 0:46Speaker 01

  The history of vitamins is miraculous because there were different deficiencies in different populations in the world, iodine included, which would cause goiter and cretinism in children, vitamin D, as I mentioned, which caused rickets, vitamin C in 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.

• 1:21Speaker 00

  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 a deficiency that they're aware of or a doctor has told them they have?

• 1:36Speaker 01

  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 fuelled this.

• 2:11Speaker 00

  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?

• 2:22Speaker 01

  I think it was probably a gradual sort 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 H E, as some people call it. And the primary promoters got people to believe that this was nutrition and it was nourishing.

• 3:00Speaker 01

  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.

• 3:35Speaker 00

  Wow.

• 3:35Speaker 01

  It was very successful.

• 3:37Speaker 00

  So the ad was saying that I was going to have my vitamin C taken away.

• 3:40Speaker 01

  Yes.

• 3:41Speaker 00

  What was this legislation going to do?

• 3:44Speaker 01

  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 US 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.

• 4:22Speaker 00

  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?

• 4:34Speaker 01

  Couldn't be more different. So a drug company has to undergo a series of randomised controlled trials where people are randomly assigned to either the drug or a standard treatment or 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.

• 5:19Speaker 01

  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.

• 5:33Speaker 00

  And so I'm guessing you're going to tell me that most people selling supplements do not do randomised trials of their supplement before they sell it?

• 5:42Speaker 01

  That's correct.

• 5:44Speaker 00

  Is it quite common nonetheless to do randomised trials for your supplement?

• 5:48Speaker 01

  It's actually fairly common to find randomised 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.

• 6:08Speaker 00

  Many supplements now have many different things in them, don't they? They're not just a vitamin, there's lots of different things.

• 6:14Speaker 01

  Sure.

• 6:14Speaker 00

  What's the difference between the randomised trial you're describing and saying this is based on science and I've got papers against these ingredients?

• 6:22Speaker 01

  Sure.

• 6:23Speaker 00

  Because that sounds good.

• 6:25Speaker 01

  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 randomised 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?

• 7:08Speaker 00

  So we talked a lot, I guess, about there being issues around, claims around supplements. I guess it's also true that one of the reasons that there's mistrust around science is that scientists can also make mistakes, right? And they can change their minds 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, loss of trust amongst the public.

• 7:32Speaker 01

  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 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

• 8:09Speaker 01

  saying is that the quality of the data comes from a variety of levels of evidence, where the highest level of evidence is randomised controlled trials. But the lowest evidence of just a case report or two could influence guidelines on which we base our medical practice or our dietary practices, et cetera.

• 8:36Speaker 00

  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?

• 8:46Speaker 01

  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.

• 9:25Speaker 01

  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 been identified, because these have not been studied properly in long-term studies, such as I've mentioned with the vitamin E and selenium.

• 10:03Speaker 00

  Very powerful statement. I'd love to run through a few specific vitamins that people I think will say, 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?

• 10:17Speaker 01

  No, the studies in vitamin C have shown really no, 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, 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 one of those, in one of those groups and wanna decrease the, your frequency of common cold, then perhaps vitamin C is something that you should consider, but at much lower doses than what are usually prescribed.

• 10:55Speaker 00

  And if I'm going to the gym a few times a week, don't I get to count like, um?

• 11:00Speaker 01

  Yeah, no.

• 11:01Speaker 00

  No? Okay. So you think really of no benefit?

• 11:05Speaker 01

  Really of no benefit.

• 11:06Speaker 00

  What about vitamin D?

• 11:09Speaker 01

  Oh, boy. So vitamin D is a real headache for those of us who wanna adhere to science on this. The story of vitamin D is actually kind of interesting in 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 controlled trials

• 11:51Speaker 01

  of the general population, vitamin D has not shown to have much benefit. There have been some studies in older folks that, that showed maybe a slight decrease in, 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, and of course, all of these, these have the potential for side effects and, and deleterious effects.

• 12:16Speaker 00

  So just to confirm, David, you are not taking vitamin D?

• 12:19Speaker 01

  I am not taking vitamin D.

• 12:20Speaker 00

  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?

• 12:33Speaker 01

  Right. Now, this is debated hotly in the very lowest of those levels, um, 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.

• 12:54Speaker 00

  Is there any harm from taking mega doses of vitamin D?

• 13:00Speaker 01

  Yes. Uh, vitamin D at high doses can be very toxic. There are real, potentially even deadly, consequences.

• 13:08Speaker 00

  So I think, again, particularly for people who might not have heard anyone talking about vitamins on, on previous podcasts, I think will be really shocked because I think they're generally presented as like something with no downside.

• 13:20Speaker 01

  Sure.

• 13:20Speaker 00

  Like, why not take it? It's sort of like insurance. You can't harm yourself. After all, they sell it, like, and it looks just like the things you get as medicines, and we know it's all, that's all supposed to be like, safe. So when could it be dangerous?

• 13:34Speaker 01

  Vitamin D helps regulate your calcium uptake from the intestine. And, 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

• 14:17Speaker 01

  from taking it. There is some suggestive evidence that people who take multivitamins may have a decreased incidence of dementia and some other things, but it's, 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, of wholesale supplementation, simply because you're over a certain age.

• 14:44Speaker 00

  And is that because you're cautious that potentially we're 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?

• 14:56Speaker 01

  That would be, well, both. And, and, 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've 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, uh, get people to think about this in a different way.

• 15:42Speaker 00

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• 16:26Speaker 00

  randomized controlled trial to check if it worked. The results blew us away and helped us create the formulation that we sell today. By the way, whenever we talk about Daily 30 as a good source of fiber, we're required to say that it contains four grams of total fat per serving. Obviously, that's all amazing healthy fats from plants. To get your pouch of Zoe's delicious gut supplement, visit zoe.com/daily30. Thanks for listening and see you next time.