Have you ever wondered if there’s a natural way to lower your high blood pressure, guard against Alzheimer's, lose weight, and feel better? Well as it turns out there is. Michael Greger, M.D. FACLM, founder of NutritionFacts.org, and author of the instant New York Times bestseller “How Not to Die” celebrates evidence-based nutrition to add years to our life and life to our years.

COVID-19 Series: Immune-Boosting Foods and Zinc

Should we be eating immune-boosting foods and what about zinc? Does it help slow the replication of the virus?

This episode features audio from The Immune System and COVID-19 Treatment and Would Zinc Lozenges Help with COVID-19?. Visit the video pages for all sources and doctor’s notes related to this podcast.


In our first story today – we look at some of the immune-boosting foods we should be eating.

Though there are more than 400 clinical treatment trials underway, currently there is no specific proven therapy for COVID-19. And we should not expect a vaccine or effective antiviral drug to be available any time soon, although we are developing COVID-19 vaccines at pandemic speed. Just for reference, the average vaccine takes more than a decade to develop, with an average failure rate of 94%.

Many have asked me for advice on what they can eat to help bolster their immune system. “How Not to Die from Infections” is, after all, the title of chapter five of my book How Not to Die, and I do have more than a hundred free videos online at NutritionFacts.org that reference immune function. And there are amazing studies, like randomized double-blind trials, showing, for example, that eating broccoli sprouts can reduce viral loads for influenza, decrease virus-induced inflammation, and boost our antiviral natural killer cell activity. Just from eating some broccoli sprouts! But this isn’t the flu.

I certainly support general, common sense advice to stay healthy during the crisis, put forth by trusted authorities, such as the American College of Lifestyle Medicine. This includes getting sufficient sleep (seven to nine hours), keeping active, reducing stress, staying connected—albeit remotely—to friends and family, and eating healthfully (a diet centered around whole plant foods)., The World Health Organization agrees: Fruits, vegetables, legumes—like beans, split peas, chickpeas, and lentils—nuts, and whole grains, cutting down on sugars, cutting down on meat, dairy, and junk, and cutting down on salt.

Optimal Nutritional Status for a Well-Functioning Immune System Is an Important Factor to Protect against Viral Infections.” However, one must resist the urge to jump on the snake-oily spamwagon of foods to boost your immune system, given our near-total ignorance of the immunological aspects of this new disease, because enhancing specific arms of the immune system could hypothetically even make things worse. Let me explain.

Take the example of this married couple, both the same age, admitted to the hospital on the same day for the same COVID-19 infection—fever and shortness of breath. Tragically, the wife was immunocompromised, because she was on chemo for breast cancer at the time (yikes!), whereas her husband had an intact immune system. The wife did fine, though, out of the hospital in under a week, whereas the husband ended up in intensive care. Wait, the immunocompromised patient did better? How is that possible? Because unlike other common viruses, coronaviruses have not been shown to cause a more severe disease in immunosuppressed patients. Why? Because your own immune response appears to be the main driver of lung tissue damage during infection.

Starting around the second week of symptoms, the virus can trigger what’s called a cytokine storm. It’s like an autoimmune reaction where your body over-reacts, and in attacking coronavirus, your lungs get caught in the crossfire. In the first week of the illness, it’s the virus itself that’s triggering most of your symptoms, but then in severe cases, it’s our own inflammatory response that takes over in causing most of the damage. It’s striking that many of our innate immune-signaling pathways, these cytokine chemical messengers our immune cells release, are aimed at killing off our own cells. But that makes total sense. The virus turns our own cells against us into little virus factories, so it’s part of our own antiviral defense to kill off our own cells to dead-end viral replication. Viruses can’t replicate in dead cells, so cell suicide is like a way to create firebreaks. But in burning down the village in order to save it, we may not survive the process.

This has led some to consider immunosuppression as a treatment for severe COVID-19, but of course immunosuppression for hyperinflammation in COVID-19 might be a double-edged sword. So, when you see that broccoli sprouts can whip up natural killer cell activity within two days, is that a good thing or a bad thing for COVID-19? It was good for seasonal flu, but who knows with this new coronavirus.

Young children have relatively immature immune systems, and normally suffer disproportionally from viral infections such as the flu––but not, apparently, from COVD-19 or SARS or MERS, for that matter, the other two deadly coronaviruses. It’s interesting; one theory as to why children seem protected suggests that greater pre-existing exposure to common-cold coronaviruses offers kids some cross-protection against the new virus. But ironically, a competing theory suggests it’s their lack of exposure to similar viruses that’s safeguarding them. There’s a phenomenon known as ADE, antibody-dependent enhancement, a phenomenon first described more than 50 years ago. In most cases, the antibodies our bodies make to target pathogens neutralize them or, at the very least, tag the invaders for removal. Sometimes, though, antibodies can actually facilitate viral infection and exacerbate disease.

This may be the case with SARS, where antibodies generated against the viral spike proteins were sometimes found to promote infection. In monkeys, an experimental SARS vaccine resulted in aggravated lung damage. Now, vaccine developers are well aware of this phenomenon, and would work to ensure any commercial vaccine would be free from this failing, but it has been used to venture a guess to account for the unusual age distribution of severe COVID-19 cases.

Perhaps similar coronaviruses circulated silently decades ago, and those old enough to have been exposed to them are now experiencing exaggerated responses to COVID-19. But young people never saw them, so they don’t get the over-reaction. I’m not suggesting this speculation is true. I just use it to illustrate the complexity of our immune interactions. Viruses attack, we counterattack, and then viruses sometimes evolve to use our own counterattack in their favor.

Just a word of caution before trying to specifically boost some element of our immune system before understanding the full scope of the new threat. Given the uncertainties, the best strategy is to not get infected in the first place, especially not until effective treatments— and a functioning healthcare system—are available.

In our next story, we discover how zinc may help slow the replication of other coronaviruses, but what about SARS-CoV-2?

Given the current pandemic, “the search for potential [preventive] and therapeutic antiviral strategies is of particular and urgent interest.” So, what about zinc, which is known in some cases to have antiviral and anti-inflammatory benefits? I looked into it as a potential treatment after the fact-checking site Snopes validated that a noted virologist did indeed make a recommendation back in February to “Stock up now with zinc lozenges.” He based his supposition on the efficacy of zinc for common colds, up to 29 percent of which are caused by coronaviruses.

There’s actually a sweet backstory to that: a three-year-old girl undergoing chemotherapy for leukemia (a disease marked by low zinc levels) refused to swallow a zinc supplement. Immunosuppressed, she had just started getting a cold. Instead of swallowing the supplement, she just let it dissolve in her mouth and the cold seemed to disappear within hours. Okay, cute little anecdote, but this observation led her father—her own father—to conduct the first randomized double-blind placebo-controlled trial on zinc lozenges for the common cold.

That’s how it all started/ But there have since been more than a dozen randomized controlled trials published, and, overall, researchers have found that zinc is indeed beneficial in reducing both duration and severity of the common cold when taken within the first twenty-four hours of symptom onset. Zinc lozenges…appear to shorten colds, by about three days…with significant reductions…in nasal discharge and congestion and hoarseness, and cough.

The common cold results for zinc are often described as “mixed,” but that appears to be because some studies used zinc lozenges containing added ingredients like citric acid that strongly sequester zinc; so, little or no free zinc is actually released. They taste better, but what’s the point if you don’t actually get the zinc?

So, what’s the best way to take zinc for the common cold? Lozenges containing around 10 to 15 milligrams of zinc taken every two waking hours for a few days, starting immediately upon symptom onset, as either zinc acetate or zinc gluconate without zinc binders, such as citric acid, tartaric acid, glycine, sorbitol, or mannitol, may work best. Best…for the common cold, but what about for COVID-19?

There are a number of purported mechanisms for the potential protection afforded by zinc. The first is that it interferes with the attachment of rhinoviruses, the most common cause of the common cold, to our cells. This presumably wouldn’t help us in the case of COVID-19, since our new coronavirus utilizes a different docking receptor.

Zinc also appears to slow rhinovirus replication, at least in a petri dish. What about coronaviruses? Zinc inhibits the coronavirus that causes SARS, by interfering with the virus’s ability to replicate its genetic code, but that was in conjunction with a chemical that ferried zinc inside the cells. There are natural dietary compounds that may play a similar function, but even if viral replication were able to be slowed in your throat where the lozenge is, what we care about most is stopping replication of the COVID-19 virus in the lungs.

But a third mechanism by which zinc may help seems more promising: boosting our antiviral immunity. For example, giving zinc pills to children with severe regular pneumonia has been shown to be effective in reducing mortality as much as three-fold over placebo. Three times higher death rates in the sugar pill group. But these studies were done in countries like Uganda, India…, and Ecuador, where there may have been pre-existing zinc deficiencies. So yeah, taking zinc if you’re zinc deficient; no wonder that helps, but it’s unclear if similar benefits could be had in higher-income countries with better population-wide micronutrient status.

Some have suggested that despite the lack of clinical data—no one has yet put zinc to the test for COVID-19—maybe it could help. I’m skeptical it would be helpful in well-nourished individuals, but, if taken as directed, it shouldn’t hurt, though zinc supplements and lozenges can cause nausea, especially when taken on an empty stomach, and some other gastrointestinal symptoms. And one should never put zinc in their nose. In the drug store, you’ll find all sorts of intranasal zinc gels, sprays, and swabs that have been linked to the potentially permanent loss of one’s sense of smell.

(Oh, and happy ending: That three-year-old girl beat the cancer, never relapsed, and grew up to become a scientist herself.)

3 responses to “COVID-19 Series: Immune-Boosting Foods and Zinc

Comment Etiquette

On NutritionFacts.org, you'll find a vibrant community of nutrition enthusiasts, health professionals, and many knowledgeable users seeking to discover the healthiest diet to eat for themselves and their families. As always, our goal is to foster conversations that are insightful, engaging, and most of all, helpful – from the nutrition beginners to the experts in our community.

To do this we need your help, so here are some basic guidelines to get you started.

The Short List

To help maintain and foster a welcoming atmosphere in our comments, please refrain from rude comments, name-calling, and responding to posts that break the rules (see our full Community Guidelines for more details). We will remove any posts in violation of our rules when we see it, which will, unfortunately, include any nicer comments that may have been made in response.

Be respectful and help out our staff and volunteer health supporters by actively not replying to comments that are breaking the rules. Instead, please flag or report them by submitting a ticket to our help desk. NutritionFacts.org is made up of an incredible staff and many dedicated volunteers that work hard to ensure that the comments section runs smoothly and we spend a great deal of time reading comments from our community members.

Have a correction or suggestion for video or blog? Please contact us to let us know. Submitting a correction this way will result in a quicker fix than commenting on a thread with a suggestion or correction.

View the Full Community Guidelines

  1. The WHO say the IFR is 0.14 and given the exaggeration of the deaths the IFR might be lower, could be higher too because PCR testing could be way off. But that the number we got. Dr. Greger why can’t we move on from this topic?

  2. Does anyone recommend a zinc lozenge like the ones described as efficacious in this podcast? Those that I’ve seen all contain mannitol, sorbitol and citric acids, which as Dr Greger stated, can neutralize the physiologic benefits of the zinc.

  3. Kate,

    I’ve successfully used the on the market zinc lozenges that do contain the alcohol sugars and acids. Based on patient and my own taste buds, those that have some of the sugars are much more acceptable.

    I and my patients have found they work well, especially when used at the first signs of a cold/sore throat/etc. After a search, I did not find any products that are free from the mentioned excipients.

    Dr. Alan Kadish moderator for Dr. Greger http://www.Centerofhealth.com

Leave a Reply

Your email address will not be published. Required fields are marked *

Pin It on Pinterest

Share This