Zinc supplements are a popular cold remedy. But do they really work?
There’s a chill in the air in many places in the U.S., a sign for many to begin stocking their medicine cabinets with remedies that supposedly prevent the common cold, or at least make them feel less crappy if they do catch it. A few of my friends swear by zinc supplements at the first sign of a runny nose, sore throat, or other telltale symptoms, claiming that popping one on the reg makes their colds to clear up faster. But can zinc really help you get over a cold? I interviewed experts about whether science backs up this popular cold remedy.
Let’s back up. Zinc is a mineral naturally found in meat, shellfish, chickpeas, and other foods, according to the National Institutes of Health’s Office of Dietary Supplements. You can buy zinc supplements, and many cold lozenges and drugs marketed as cold remedies contain zinc.
Zinc is “one of those things that is necessary in a lot different functions in the body, and some of those do relate back to the common cold or anti-infection,” Evelyn R. Hermes-DeSantis, clinical professor at the Rutgers Ernest Mario School of Pharmacy, tells me. That’s the origin of the rationale for taking it when you start experiencing cold symptoms: If your body needs zinc to help fight infections, then taking it can prevent infections — right?
It make sense, in theory, Hermes-DeSantis says. How it actually plays out, though, is a different story. She cites an analysis that homed in on eight clinical trials that looked at zinc and the common cold. In these randomized, placebo-controlled clinical trials, researchers randomly assigned participants to take either zinc or a placebo to ensure that any benefit observed in the treatment group was due to zinc, not to chance.
The findings suggested that if you take a lozenge containing between 10 and 20 milligrams of zinc every two hours while you’re awake, starting within two days of your symptoms appearing, your cold might last up to three days less than it would’ve if you hadn’t taken zinc. The problem is, “it was a mixed bag,” DeSantis says. A couple of the trials showed that zinc had no benefit.
And it might be hard to have confidence in even randomized, placebo-controlled clinical trials of zinc. To avoid bias in such trials, participants (and researchers) shouldn’t know whether they received a placebo or the treatment— but that’s not really possible if the treatment is zinc. “The thing about zinc is, it tastes pretty terrible,” says Stuart Campbell Ray, a professor of infectious diseases at Johns Hopkins Medicine, adding that it’s hard to create a placebo that tastes like zinc.
Plus, when an intervention “is obnoxious, if it hurts a little or tastes bad, it tends to have a placebo effect,” Ray says. In other words, it can be tricky to tease apart whether any potential benefits observed really were due to the zinc, or a placebo effect.
In other words, evidence of whether zinc can shorten the duration of a cold isn’t that strong. But can it prevent colds, say, if you take it regularly before cold season starts? “That data is even worse,” DeSantis says, and the little that exists “is really conflicting.”
As for whether zinc can help with the coronavirus, “we don’t have evidence that zinc helps with anything like COVID-19 or any other viruses,” Ray says.
At best, zinc might shorten the duration of your cold by a few days — and the cost for this pretty modest, uncertain payoff is pretty steep. Not only does it have a weird metallic taste, it can also cause dry mouth, Hermes-DeSantis says. “I’ve tried a zinc lozenge, and I had the worst cotton mouth in the world,” she recalls. Ray adds that people who take zinc lozenges are also more likely to have a distorted sense of taste in general. Nausea is another possible side effect.
“I’m all for a safe placebo, but I’m worried people can overdo it with zinc,” says Ray, who recommends consuming no more than the product label recommends, if you do insist on taking it. If you take it for a prolonged period of time — for months on end — you can end up with anemia, a condition in which you don’t have enough healthy, oxygen-carrying red blood cells, Hermes-DeSantis says. She points out that anemia can make you tired and more prone to infection. The FDA has also cautioned against using intranasal spray containing zinc after many people who used them complained that they’d lost their sense of smell, leading to recalls of such products.
If you’re on any sort of medication, check with your doctor or pharmacist before you start taking supplements, Hermes-DeSantis says. You’ll want to avoid zinc if you’re on medication to control your blood sugar, since zinc may also lower your blood sugar. Zinc can also bind certain drugs, including some antibiotics and drugs to treat HIV, so that your body doesn’t absorb them. It can counteract diuretics, too, often used to control blood pressure, Ray says.
If your doctor has told that you have a zinc deficiency, then supplements might be a good idea, Ray says. Zinc deficiency isn’t that common, though. “It’s really not hard to get enough in your diet.” If you don't have a zinc deficiency, and you’re taking zinc supplements just to prevent a cold or get over a cold faster, you’re throwing money at something that might not help you, and could even have some not-so-fun side effects.
The take home-message: “If it works for you, and you can tolerate it, fine,” Hermes-DeSantis says, “but it’s probably not going to work for a lot of people.”