Research Says Zinc Can Shorten The Common Cold It's possible — but it depends on a few key factors. NPR health correspondent Allison Aubrey explains, and tells the story of the scientist who uncovered the importance of zinc for human health in the first place.

Follow Allison on Twitter @AubreyNPRFood and host Maddie Sofia @maddie_sofia. Email the show at shortwave@npr.org.
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Can Taking Zinc Help Shorten Your Cold?

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Can Taking Zinc Help Shorten Your Cold?

Can Taking Zinc Help Shorten Your Cold?

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MADDIE SOFIA, HOST:

You're listening to SHORT WAVE from NPR. Maddie Sofia here with NPR health correspondent Allison Aubrey. Hey, Allison.

ALLISON AUBREY, BYLINE: Hey, Maddie.

SOFIA: So we are right in the middle of cold and flu season. And, Allison...

AUBREY: Yep.

SOFIA: ...As our consumer health aficionado, let's start with talking about how to reduce the likelihood of getting a cold.

AUBREY: OK.

SOFIA: There's our SHORT WAVE favorite, which is washing your hands, of course.

AUBREY: Sure. And, you know, Maddie, not everybody who gets exposed to a cold actually gets sick. So when they've done these studies where they take rhinovirus and they stick it up people's noses and they see who gets sick and who doesn't, they find that people who've slept less than six hours are about twice as likely to get sick when exposed to this cold virus as compared to people who've slept more. So sleep is really important. High stress has been shown to increase the likelihood. And a lack of exercise has also been shown to make you more susceptible.

SOFIA: I feel like you just targeted me with the high stress and lack of exercise...

AUBREY: Oh, stop. No. Stop, stop, stop. No, I am not here to wag my finger at you or anyone else because at a certain point - look - we all get a cold. Typically, adults in the U.S. get about two to three colds a year. And when you do get a cold, there is something you can do to put yourself out of so much misery.

SOFIA: One method people swear by is zinc, right?

AUBREY: That's right. It's a mineral found in trace amounts in a lot of the foods that we eat. Our bodies need zinc to function optimally. In fact, it's considered an essential mineral. And boosting the amount of zinc you get during a cold by sucking on zinc lozenges is actually shown in a bunch of studies to help shorten the length of the common cold but only in certain situations. And there are a lot of caveats.

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SOFIA: So today on the show, zinc, an essential mineral and a cold remedy. We'll talk about when it works and when it doesn't.

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SOFIA: OK, Allison, we're talking about zinc and whether or not it helps shorten the length of a cold. And there's a story behind that question that starts in the 1960s?

AUBREY: Yep, that's right. That is when a young physician named Ananda Prasad studied a group of young Egyptian men who were completely deficient in zinc. Now, these young men suffered from stunting. They hadn't grown to a normal height or developed normally in other ways. And this is because they had very limited diets. They ate a lot of bread that was high in phosphate. And that can actually block the absorption of zinc.

SOFIA: OK.

AUBREY: Now skip ahead. Prasad is now 91 years old. He is still an active researcher at Wayne State University in Detroit.

SOFIA: Wow.

AUBREY: And he told me that when he gave these young men zinc, something really remarkable happened.

ANANDA PRASAD: They grew at a rate of 5 to 6 inches in height the first year. So it was a really remarkable, remarkable change that occurred after supplementation.

AUBREY: When you first documented this, what was your - you must have been ecstatic.

PRASAD: (Laughter) Well, actually, the first patient we gave zinc and he has started to grow, I couldn't believe it because I thought that the growth phenomena will be all shut off after the age of 18, and nothing will happen to anybody. But that was not the case.

SOFIA: So does that mean that we all need zinc to grow?

AUBREY: Right. Well, we all do need zinc for optimal health. It doesn't work like a growth hormone.

SOFIA: Sure.

AUBREY: And here in wealthier nations, it's completely possible to get enough zinc in your regular diet. But back in the 1960s, the role of zinc was not at all understood. I mean, people thought Prasad was crazy for just suggesting that zinc deficiency could do this. But he ignored all those people who were skeptics. He just kept pressing on. He became really just kind of obsessed with getting to the bottom of, how does zinc work in the body? And so after he documented the growth in these young men, he threw himself into further studies. He really laid the groundwork by showing that zinc influences immunity. He theorized that zinc works as an anti-inflammatory agent.

SOFIA: OK.

AUBREY: And then over the course of a couple decades, Prasad and other scientists have shown that up to 300 enzymes require zinc for their activation or stability of their structure.

SOFIA: Right, like, enzymes that you would even be familiar with, like alcohol dehydrogenase, which is...

AUBREY: Which is - rolls right off the tongue.

SOFIA: Yeah.

(LAUGHTER)

SOFIA: But, importantly, breaks down all that beer and wine you drink, the alcohol in those.

AUBREY: Oh, right, right. Exactly. But, you know, keep in mind, it took decades to show this. I mean, lots of scientists completely questioned Prasad's findings. But eventually in 1974, the National Academy of Sciences declared zinc an essential mineral for human health. And they established a recommended daily intake level.

SOFIA: What is that level, Allison? Because now I'm a little worried...

AUBREY: (Laughter).

SOFIA: ...About my zinc levels, perhaps.

AUBREY: Sure. Well, public health officials say that adult men need about 11 milligrams of zinc per day, women about 8 milligrams.

SOFIA: OK.

AUBREY: So let me help you figure this out. If you ate a 3 oz beef chuck roast...

SOFIA: OK.

AUBREY: ...You'd get about 7 milligrams. So red meat can be quite high. That's close to a day's amount. A half cup of beans will get you about 3 milligrams. Pumpkin seeds - a single ounce provides 2.2 milligrams, so that's a good source. And then there are lots of cereal grains that are fortified with zinc.

SOFIA: Right. That's why I eat a bowl of cereal every night at 11 p.m.

AUBREY: (Laughter).

SOFIA: It's for my zinc.

AUBREY: That's right. You are clearly not zinc deficient. Here's a fun fact - oysters have more zinc per serving than any other food. They contain 74 milligrams per a 3 oz serving.

SOFIA: Honestly, that feels like too much zinc.

AUBREY: (Laughter) I know. Now, overall - we shouldn't laugh. I mean, overall, here in North America, overt zinc deficiency is pretty uncommon. But let me get back to the story of Dr. Prasad and his discoveries.

SOFIA: Yeah, yeah.

AUBREY: Now, these zinc guidelines were first put into effect in 1974. And once that happened, Prasad began to wonder, since he knew that zinc had an effect on immunity, whether zinc supplements might help to shorten the duration and symptoms of a common cold. And I should say that he kind of came at this from what he had realized back in Egypt. He had seen that a lot of these deficient men died early from infections...

SOFIA: Oh.

AUBREY: ...So his guess was that, yes, zinc, lo and behold, probably did play this role in immunity. Now, it's known, for instance, that the body requires zinc to develop and activate T lymphocytes. You know what those are?

SOFIA: Yeah. Yeah, they're, like - protect you against viruses and cancer.

AUBREY: Totally, exactly. They're the little soldiers that come out to protect you. They're the type of white blood cell that is a key part of the immune system. So this was all kind of in the back of his mind. He wanted to test out whether these zinc supplements might help shorten a cold. So he collaborated with a scientist, a fellow scientist named Tom Fitzgerald at the University of Michigan. I talked to Fitzgerald. And he told me, you know what? When Prasad first gave him this theory, he was pretty skeptical.

TOM FITZGERALD: I got to admit when I first heard this, I actually told the research assistant, I think he's losing it.

SOFIA: Why was he so skeptical other than just being a scientist, so therefore being skeptical?

AUBREY: Yeah. Right, exactly. You know, I guess he was skeptical that something as basic as a mineral would be powerful enough on its own...

SOFIA: Right.

AUBREY: ...To alter immune function, which is a good level of skepticism. But he did agree to do the study. They recruited a whole bunch of people in Detroit who had colds. They gave them zinc lozenges made by a pharmacist. It was a double-blind, placebo-controlled trial, so that means that neither the participants nor the researchers knew who was getting the real thing and who was getting the placebo. And here's what they found.

FITZGERALD: Lo and behold, when I did the analysis, it indeed did shorten common cold symptoms by about two or three days. And I got them. And I was stunned by that result.

SOFIA: Two or three days isn't nothing.

AUBREY: No, not at all. When you think about how many lost work and school days there are just because of cold symptoms...

SOFIA: Yeah.

AUBREY: ...That's significant.

SOFIA: Absolutely.

AUBREY: And then several other studies have confirmed these findings. I talked to another scientist. His name is Harri Hemila of the University of Helsinki in Finland. He published a sort of meta-analysis that reviewed a bunch of the studies. And he says bottom line here is low doses of zinc lozenges don't work. You got to take about 80 to 90 milligrams a day of zinc at the onset of a cold. That has been shown to help shorten it. And he says he now uses zinc when he feels a cold coming on himself.

HARRI HEMILA: I'm also encouraging my patients to try zinc. But usually, I am encouraging only if the common cold has been lasting for a day or something like that.

SOFIA: So he's saying only within the first day.

AUBREY: That's right because if you don't catch it at the beginning, you can't really halt the progression. It doesn't work.

SOFIA: OK. So if you're taking zinc at the beginning of a cold, it has to be within the first 24 hours.

AUBREY: That's what the studies have shown.

SOFIA: OK.

AUBREY: But here is another caveat, and it's a pretty big one. If you go to the drugstore right now and you find a zinc product, a lot of what you'll find are these multi-ingredient products. You'll see zinc with a whole bunch of other ingredients you probably have never heard of before. Be aware that a lot of ingredients can undercut the effectiveness. For instance, some of them contain citric acid, which actually binds with the zinc and makes it completely ineffective.

SOFIA: So you're basically saying you've got to take it early. You've got to take at least 80 to 90 milligrams. And avoid stuff with citric acid.

AUBREY: That's right. And as the consumer health reporter here, I want to be able to say, you know, go out and buy this product. Unfortunately, I can't do that because the lozenges used in the clinical trial - those are not commercially available. And here's the deal - a lot of times, manufacturers change their ingredients. They change dosing. It's hard to make a solid recommendation about a product. You just basically have to do your homework. You got to be aware that you need a certain dose and that you don't want all these other ingredients.

SOFIA: Right.

AUBREY: I think it's more - what you can feel assured of is that there's science behind the idea that, yes, zinc can help shorten a cold.

SOFIA: Would you be comfortable saying, hey, go out there and eat a couple oysters?

AUBREY: You know, if you're a seafood lover, absolutely. Go enjoy some oysters. I can't tell you whether or not they're an aphrodisiac, but I can tell you they've got plenty of zinc.

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SOFIA: (Laughter) Allison Aubrey, thanks for the advice.

AUBREY: Thanks, Maddie.

SOFIA: Hey, you, listening to this, I am positive you've recommended SHORT WAVE to your friends, family, loved ones, acquaintances and co-workers. But if you want to help recommend it to complete strangers, do us a favor and rate us and review us in Apple Podcasts. That will help more people find our little show, OK? OK.

This episode was produced by Brent Baughman, edited by Viet Le and fact-checked by Emily Vaughn. I'm Maddie Sofia. We're back tomorrow with more SHORT WAVE from NPR.

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