Leah:

Hello and welcome to the Ideal Nutrition Podcast. I’m your host, Leah Higl, and I’m here with my co-host Aiden Muir. And today we’ll be covering the topic of zinc. Specifically in the context of immunity, and if taking zinc does help with the prevention of the common cold or other respiratory tract infections and/ or reducing the severity and duration of these particular things. So starting with how zinc works or what it does in the body.

Zinc supports the development and function of immune cells, including T cells, B cells, and other immune cells, which are involved in fighting infections and maintaining overall health. Now, we do know zinc deficiency can weaken the immune system, making individuals more susceptible to infections, particularly in children and older adults.

And that raises a few more questions and answers. For example, does adding more zinc still help if somebody wasn’t deficient? Is it still going to have that impact? And also, how common is deficiency?

Aidan:

So, on the topic of how common deficiency is, it is surprisingly hard to get good stats on this. When I make claims on this podcast, in many cases, if you go to our show notes, you’ll see references for the claims. When I was looking at stats on this, I was like, yeah, I’ll reference some stuff here. The first one or the best one I kind of found was from like 1992. I was on the fence. I was like, do I use this? It’s hang on, it’s 2025. People are reading different stuff now, surely than they were in 1992.

And cause I didn’t find anything better. I was like, you know what? I’m going to go a different route on this one. And I would rather have a bit of a ballpark than perfect stats, not a perfectionist. You can make of this information what you will. What I did was I went to chat GPT and I’ve used this for a lot of stuff like this, surprisingly, not on the podcast, just in my own life, you know?

And I asked the question, if you had to give an estimate of what percentage of people in Australia is zinc deficient, what would you say? Actually, the first one I did was in relation to what percentage of people do you think meet the recommended daily intake? And it speculated 20 to 40 % don’t hit the recommended daily intake. So, 20 to 40 % are below that. With actual deficiency, it estimated five to 10 % in Australia.

Outside Australia, it’s likely higher in certain countries and people who are either plant-based and/ or older tend to be at higher risk of deficiency than that five to 10 % kind of stat would give. It’s worth noting that a blood test does seem to be the best way to test for this at the moment, but can have 20 % variability within day.

There aren’t easily accessible better alternatives, but it’s worth knowing that the accuracy isn’t incredible. When I was reading into that a fair bit as well, I was looking at like how much to changes in dietary intake change your blood tests. And like there were cases people were looking at where they noticeably increase their dietary intake and their average blood value of zinc increased by about 6%. So 20 % variability is actually quite high.

As I said, make of this information what you will. Those aren’t legitimate stats, but based on what I have seen and what I’ve observed, they do seem to be pretty fair estimates to me and that’s kind of what I’d say without having better stats.

Leah:

So, what does the research show when it comes to this particular topic? There are three separate categories that we are looking at from an outcome point of view. We’re looking at prevention of developing these infections, as well as the symptom severity and the symptom duration.

The main study we want to point to that summarised all of this quite well included 34 randomised control trials and a sample size of over 8,000 participants. Roughly half the studies looked at prevention and half looked at recovery. Now they use different forms of zinc but mostly they were lozenges and the dosages ranged from 45 milligrams up to 276 milligrams per day.

And just highlighting how that is that the upper limit for zinc is 40 milligrams per day. So, 276 milligrams is a very large amount of zinc. And the RDI, to add a little bit more context, is eight milligrams for women and 14 milligrams for men per day. Once again, in relation to those RDIs, the intake or the supplemental amount of zinc is very high.

Aidan:

Something I personally find humbling as a content creator in the nutrition space is whenever I’ve written content on a topic and then a meta analysis comes out after and like I’ve gone through and tried to find as many studies on the topic as I can. And I’ve come out with a number being like, as far as I there’s X amount of studies and then a meta analysis comes out with 34. I’ve previously written about zinc and immunity.

The number I found was noticeably lower than 34, but I’m like, it’s cool. And like that study came out last year, so 2024. The last one I wrote that was comprehensive was like 2020, but I’m just like, I just don’t think that many studies have come out in that interim. Anyway, I do my best. But, going onto other stuff here. So, we’re going to look at more outcomes in relation to prevention. From a prevention standpoint, it didn’t make any noticeable difference with prevention.

From a duration standpoint, it helped reduce the duration slightly. The difference was an average of about two days, although there were mixed outcomes in relation to that topic, even on this podcast, I’ve spoken about this previously, there was one study I remember reading on this where people’s duration of being sick increased by seven days. Like, obviously zinc has not caused that. Like this is just a small sample size study.

That group was probably just going to be sick for longer. Right? But it does give a bit of an insight that there are mixed findings, but once you’re at the point, you have 34 randomized control trials, over 8,000 participants, I’m starting to take the two day reduction in duration actually pretty seriously at that stage. Symptom severity didn’t change, although obviously with the reduction in duration, it’s still a net positive from what we are seeing.

Leah:

The consensus based on research is that you should start taking zinc supplements within 24 hours of actually noticing the symptoms if this is something that you wanted to do. It doesn’t really make that much sense to take all year round. A surprisingly high percentage of people do report adverse side effects to supplementing zinc, particularly at these kinds of higher dosages.

The main ones are going to be nauseousness as well as taste disturbances. And honestly, it’s high enough in terms of people citing the side effects that it’s worth factoring in whether or not it’s actually worthwhile. For context, the studies were done in a pretty wide range of countries. So, we’re not just thinking like Australia, America, England, like there were some noticeably different countries to Australia in there. And we’d probably make the wager that there is a much lower zinc intake in some of those countries.

As opposed to Australia, where nutrition overall may be harder to get for individuals, like being nourished overall, food access, all that kind of jazz. So, we could speculate that the effectiveness would scale a bit based on baseline zinc intake. Perhaps this is something that would be more effective in a country with a baseline that’s lower than in more your first world countries where the baseline is probably higher.

Aidan:

Now, very briefly touching on food versus supplements. So, you could probably tell from the amounts that were being spoken about that food probably isn’t necessarily as realistic of a way. You can piece it together being like if the recommended daily intake is 8 mg for women, 14 mg for men, the top end of the dosage is what did you talk about? Like 200 and?

Leah:

Yes, 276 or something.

Aidan:

Yes, super high. Very big gap there. And then we also touched on chat GPT’s estimate of like 20 to 40 % of people aren’t getting enough through food anyway to meet the recommended daily intake. You can be like, okay, it’s pretty hard to get to these really high doses.

So, you can already piece some stuff together just from that. Although zinc supplementation doesn’t reduce the risk of getting sick noticeably at a population level, it’s a pretty safe bet that being deficient probably does increase your risk of getting sick. At a minimum, you want a good enough food intake to avoid deficiency if you can.

So, getting a decent amount through food is always a good starting point. There’s not any evidence that I’m aware of that getting high zinc intakes from food while sick will help noticeably, but I would say it’s always worth trying to aim for a nutrient rich diet. I just wouldn’t be overly focused on that.

Leah:

Now, the next thing we’re going to discuss is more about the method in which we are consuming this supplemental zinc. And in a lot of the research, you will note that lozenges are quite a common way to supplement zinc in the space of researching upper respiratory tract infections and things along those lines.

And you could go like, well, why? Why lozenges? And it’s a pretty simple answer. It’s because lozenges slowly release zinc in your mouth and then actually into the upper respiratory tract, which is where the cold viruses are living and where they’re replicating. So, this is another argument for supplementing potentially rather than just getting it through food. It’s like this very specific way of doing it.

Aidan:

In terms of how to take if you want to take it, the dosages are quite high, but I’d personally be looking at 50 to 75 milligrams per day from what I’ve seen. So, it’s lower than the top end of that, but just above the bottom end of what we’ve typically seen in research. I’d also only do it for three to seven days. One reason why I wouldn’t go higher or longer than that is beyond just the frequency of mild side effects.

And for reference, like in that review that had over 8,000 people, it seemed that just over 2000 people reported some form of side effect. That’s high. I didn’t dig deep into the details being like how severe is every case by case and stuff like that, but that’s pretty high. So, beyond just like the side effects, you can also impact absorption of other nutrients. Copper is one of these examples where theoretically you could throw off the balance by going too high for too long.

So, if you were to take it for those three to seven days and immediately upon getting sick or noticing symptoms, to also optimise it you would want to split the dosage across the day. So, using those lozenges, you’d be aiming for like five to six lozenges across the day to add up to around that 50 to 75 milligram target. Note that that is just my personal thoughts on it. Like, if your lozenges added up to 85 milligrams, it’s fine.

I just wouldn’t go towards the top end and I’ll just spread it out across the day. And if you think about it from that lozenges perspective, it kind of means you have more exposure to zinc hitting those areas and upper respiratory tract and areas that we’re kind of looking at for longer across the day.

Leah:

To summarise, zinc does potentially help reduce the duration of symptoms. So, it could be worth trialing. But, ultimately, it doesn’t necessarily help with the prevention or severity of the common cold or upper respiratory tract infections. And it also has the potential to come alongside several downsides that are worth being aware of. It’s kind of just weighing up the pros and cons when we’re thinking about do we or do we not want to take this approach when we are getting sick?

This has been episode 214 of the Ideal Nutrition Podcast. If you haven’t yet left a rating or review, it’s always greatly appreciated for you to do so. But otherwise, thanks for tuning in.