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Can Vitamin C and Zinc Help Cure Colds

Nobody enjoys the aches, cough, and stuffy nose that comes with a cold, so it’s no surprise that we spend a ton of money on over-the-counter symptom relief — $3 billion a year in the US alone. And you’ve probably heard all sorts of tips and tricks to keep from getting sick: Drink some OJ for the vitamin C. Or spray some zinc into your nose. But it turns out that none of those popular cure-alls actually work. Take vitamin C, for example. It rose to fame as a cold-busting immuno-booster in 1970 when Nobel Prize-winning chemist Linus Pauling published a book promoting what he called “megadoses” of vitamin C. Since he was so famous, the idea that vitamin C could cure colds spread quickly, even though it wasn’t backed by solid science or the medical community. It’s not hard to see why he was so enamored with vitamin C — it’s involved in a ton of biological processes, including regulating how your genes are expressed. It’s so important that most animals synthesize it on their own; we humans are in the minority, because we don’t have that ability and have to get it from our diet. Now a vitamin C deficiency does decrease your ability to fight off some infections, and the most severe form, scurvy, can be fatal. But if you don’t have a deficiency, the evidence for boosting your immunity with extra vitamin C is pretty shaky. A 2013 review pooled data from 29 studies with more than 10,000 participants and found that taking extra vitamin C had no effect on the number of colds a person got. Some studies found that taking extra vitamin C during a cold could shorten it slightly, but when other studies tested that, the effect wasn’t replicated. Overall, the reviewers didn’t recommend taking vitamin C unless you’re undergoing extreme physical stress — like if you’re a marathon runner or doing military training in the subarctic. So, if you’re planning on exploring the frigid tundra Hoth-style, it might be helpful. But otherwise, don’t bother. The evidence isn’t much better for zinc, although there’s a lot more controversy about it. Like with vitamin C, the idea of taking zinc is based on what happens to people with severe deficiencies. Zinc is an essential component of all kinds of cellular processes, like DNA replication and cell division. People with zinc deficiencies have severe immune dysfunction, and many die from infections. Since too little zinc is so devastating, the idea that more zinc equals more immunity might seem like a sensible leap. But a review of the available research, also published in 2013, was lukewarm. There was no evidence that zinc prevented colds, and the only thing it seemed to do was make colds shorter, as long as you took it within 24 hours of the first symptoms. But there are a bunch of reasons to be cautious about that finding. For one thing, it’s really hard to compare the studies on zinc in a scientific way, because there’s no standard formula or dosage. The earlier version of the review, published in 2007, was withdrawn, and so was the 2015 update. That’s how hard it is to draw conclusions from the research that’s been done so far. And even if it does work, the side effects can be pretty awful. Many studies suggest taking more than 75 milligrams of zinc every day for effective treatment, but the Institute of Medicine says the tolerable upper limit is only 40 milligrams a day. Even at that dose, a lot of people notice a bad taste and get nauseous. And the nasal sprays have been linked to more than 100 cases of anosmia — the loss of the ability to smell. As for the almost unlimited number of herbal supplements, tonics, and teas that promise to help you dodge or cure colds ... very few of them have been studied extensively. Not even echinacea, a long-time favorite in the herbal cold and flu arsenal, has science on its side: a 2014 review found no benefit from anything with echinacea in it. And that’s assuming these supplements actually contain the advertised ingredients. An investigation of herbal supplements by the New York State Attorney General’s office found that four out of five products didn’t contain any of what they listed on the box. At this point, you’re probably wondering if there’s anything you can do to prevent colds or get rid of them more quickly once you have them. Unfortunately … no. Not really. Nasal decongestants, over-the-counter cough medicine, and antihistamines all show little to no benefit when it comes to decreasing cold duration or severity. That said, they can still make you feel better by helping with the symptoms. It’s also probably good advice to rest, stay hydrated, and try not to spread your germs to all your friends and coworkers. And while you’re resting, take comfort in the knowledge that there are researchers out there working on antiviral drugs and vaccines for the common cold. They haven’t found much yet, but they are trying. Thanks for watching this episode of SciShow, which was brought to you by our patrons on Patreon. If you want to help support this show, you can go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow and subscribe!

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