Can Dietary Supplements Help Fight COVID-19?

Since the beginning of the COVID-19 pandemic, I have received a deluge of questions from people who would like to know which dietary supplements they should take to prevent being infected by the coronavirus. People have asked me how much zinc, elderberry, or vitamin C they should take to boost their immune system. Some friends have even asked me if taking high doses of vitamin C would make them so immune to infection that they would not need to wear a mask. The majority of these questions start with a simple statement like “I read on the internet (blogs, social media, etc.) that taking elderberry would boost my immune system or it would kill the virus.” One person asked me if she should take colloidal silver at a much higher dose than she usually takes. I told her absolutely not, then proceeded to share all of the side effects of a colloidal silver overdose, or any dose. While an uptick in dietary supplement usage or dosage may not seem significant, the lack of knowledge and misinformation around the pandemic are a significant cause for concern. In recent months, the sales of dietary supplements have surged nationwide (and worldwide) as scared consumers view what they see on TV commercials, blogs, and social media posts as scientific evidence in support of using dietary supplements. However, when it comes to the underlying science about this novel coronavirus, much still needs to be learned.

For those who might be too busy or do not want to read this section in detail, below is the abridged version of my response to these questions:

There is insufficient evidence supporting a therapeutic role for any dietary supplements to prevent or treat COVID-19, and using dietary supplements in high doses can be harmful. If you have low levels of vitamin D, I recommend that you take a vitamin D supplement, get safe sun exposure, and eat foods rich in vitamin D. For now, to boost your immune system, I recommend that you eat a nutritious diet rich in fresh (or frozen) fruits and vegetables, get at least seven to eight hours of sleep per night, exercise, and manage your stress.

For those who are interested in learning more about the efficacy and safety of dietary supplements in the context of COVID-19, this section highlights some immune-related compounds that many have been asking about. While not exhaustive, this section seeks to give you a better understanding of the current science about using dietary supplements to prevent COVID-19.

Since the onset of the COVID-19 pandemic, sales of dietary supplements have skyrocketed worldwide, especially the ones with claims to boost the immune system. Sales of supplements such as elderberry, zinc, vitamin C, and echinacea increased by 415%, 255%, 146%, and 122% respectively in the week ending March 8, 2020 (Information Resources Inc., 2021). While these drastic increases might seem like typographical errors, market research suggests that this was simply the start of an upward trend, as people around the world have sought ways to combat the spread of the virus (Information Resources Inc., 2021). The nutritional supplement industry in the United States saw a net gain of $345 million in 2019. During the first six weeks of the coronavirus pandemic (until April 5, 2020), sales of nutritional supplements experienced a net gain of $435 million, and in the following six weeks (until May 17, 2020), sales of these supplements gained another $151 million. In recent months, these sales rates have begun leveling off, but when compared to previous years, the net gains are still significantly higher. For instance, sale of vitamins appears to be higher by 16% in 2020, when compared to 2019. The rate of increase is more than three times what it was in 2019, when sales surpassed those of 2018 by only 5% (Information Resources Inc., 2021; SPINS, 2021).

There is no doubt that we are all panicked, and we tend to buy dietary supplements based on emotional decisions and not logical ones. There are several reasons for this increase in sales, but the driving force appears to be unproven claims by medical entertainment personalities and dietary supplement manufacturers on television programs and social media platforms. They promote the use of dietary supplements such as vitamin C, elderberry, zinc, and vitamin D to either prevent or cure COVID-19. And with limited scientific evidence available on COVID-19, as research is ongoing, misinformation has been able to spread across the worldwide web, creating what the World Health Organization refers to as an “infodemic” (World Health Organization, 2020). Analyses of Google trends have revealed that searches for dietary supplements, herbs, and other bioactive compounds experienced a sharp uptick at the height of the pandemic, when global quarantine efforts were well underway (Hamulka et al., 2021). 

However, interest in particular compounds have waxed and waned, as trends have brought each into focus for their general immune-boosting or antiviral properties (Hamulka et al., 2021).

Let’s talk about a few commonly used dietary supplements that have been heavily marketed for the management of COVID-19. In some of the marketing campaign of these supplements, we see phrases such as “proven scientifically” or “been shown scientifically to kill the novel coronavirus that causes COVID- 19.” To better understand the underlying science, and the gap that is not often addressed in this language, please review chapter 4 (The Science of Dietary Supplements) in this book. While these phrases make it sound like sufficient evidence exists, the results of an experiment in a petri dish that discovered that elderberry exhibited antiviral activity against human coronavirus cannot be extrapolated to COVID-19. And anecdotal reports from a few people who took elderberry and did not get COVID-19 do not constitute scientific evidence either.

Science takes vast amounts of time and resources to come to reliable and reproducible results. During a rapidly-changing public health crisis like the COVID-19 pandemic, the time required to come to scientific conclusions can seem extraordinary. But this allows scientists, healthcare professionals, and the general public to make informed decisions. So, as always, before you start taking any dietary supplements, talk to your physician or healthcare provider to make sure that you are taking the correct dose and that they are not interacting with other drugs that you may be taking. Although we are still learning every day about diseases like COVID-19, we already have some basic knowledge about how some dietary supplements such as vitamins work. Let’s take a look at some of the most widely discussed supplements over the course of the pandemic.


The scientific studies that evaluated the efficacy of vitamin D for COVID- 19 point in a common direction: Vitamin D deficiency may make people more prone to become infected and develop COVID-19 (Adams et al., 2020). Some reports suggested that administration of vitamin D to patients with COVID-19 who are hospitalized can shorten the length of hospital stay, but as of now, randomized trials have not proven that these reports are accurate (Hernández et al., 2020; Ohaegbulam et al., 2020). My recommendation is that you check your 25-hydroxyvitamin D levels. If they are less than 25 nmol/L, then you need to take vitamin D supplements. Consumption of high doses of vitamin D (often in excess of 4000 IU per day) can result in adverse effects including high levels of calcium, so it’s important to monitor your intake.


Clinical trials on the use of vitamin C in common cold collectively suggest that regular use of vitamin C can shorten the duration of the common cold by 8% (Hemilä & Chalker, 2013). However, we cannot extrapolate the results of these studies to COVID-19 because COVID-19 is caused by a novel coronavirus that is genetically different from the coronavirus that causes the common cold (Wang et al., 2020). There are a number of claims on the effectiveness of high-dose vitamin C, both orally and intravenously, but at the time of this writing there is no scientific evidence to prove that vitamin C can be taken to prevent or treat COVID-19. In a randomized clinical trial that tested the effectiveness of a daily intake of high-dose zinc (50 mg), vitamin C (8000 mg), both agents, or standard of care for ten days in ambulatory patients with COVID-19, it was reported that neither zinc, vitamin C, nor their combination significantly decreased the duration of the symptoms associated with COVID-19 (Thomas et al., 2021). I recommend that you consume vitamin C–rich fruits and vegetables to have adequate intake of vitamin C. High doses of vitamin C may result in gastrointestinal side effects such as nausea, vomiting, heartburn, and diarrhea and can also cause the formation of kidney stones.


Zinc has been promoted to treat and prevent the common cold, although the results of studies (most of them with low-quality methodologies) that evaluated the impact of zinc on the common cold are conflicting. One of the most comprehensive systemic reviews of clinical studies on zinc concluded that zinc supplementation may reduce the duration of the common cold by 1.65 days (Science et al., 2012). However, when it comes to COVID-19, a recent retrospective analysis showed that there was no association between supplementation with zinc and survival in hospitalized patients with COVID-19 (Yao et al., 2020). This study was retrospective and the zinc levels were not measured, and some critics indicated that measuring the zinc levels of the patients who received zinc supplementation would have resulted in a different conclusion (Khurana et al., 2021). Although zinc at oral doses below 40 mg/day is considered safe, higher doses can result in gastrointestinal adverse events and loss of taste. Zinc should never be used nasally because it may result in permanent loss of taste (Jafek et al., 2004).


Elderberry is reported to have antiviral properties due to its ability to modulate inflammation (Thomas et al., 2020). However, the results of clinical studies on the efficacy of elderberry to prevent or treat the common cold are conflicting (Mahboubi, 2020). This is mostly due to the low quality of such studies, which include small sample sizes and lack of sound statistical analyses, and the fact that most of these studies were funded by the companies that sell elderberry products (Hint: Conflict of interest!). Although elderberry is derived from a naturally-occurring plant (Sambucus nigra), and the general public believes that plant-based products are largely safe, science suggests otherwise. Patients with diabetes should refrain from taking elderberry because it can interfere with insulin secretion and glucose metabolism. It has also been reported that elderberry can result in a number of cardiovascular side effects, such as low blood pressure and tachycardia (an increase in heart rate) (Ulbricht et al., 2014). Elderberry can also cause dehydration and low levels of potassium due to diuresis and can interfere with prescription drugs such as immunosuppressants (Ulbricht et al., 2014).


In 1999, the FDA issued warnings that over-the-counter products that contain silver and colloidal silver were unsafe and misbranded (FDA, 1999). Despite these warnings, colloidal silver is still widely available and is now heavily marketed as a potential preventive therapy and cure for COVID-19. The most common side effect of silver is argyria, a grayish skin discoloration that is permanent (Chung et al., 2010). Silver can also cause other serious side effects such as neurotoxicity, blood cancer, and liver and kidney disease (Keung et al., 2020). Given the significant prevalence of side effects and the guidance of the FDA, please DO NOT TAKE any dietary supplements that contain silver or colloidal silver.


While marketing campaigns and misinformation prevalent on social media platforms would suggest otherwise, the best method for prevention of COVID- 19 (as with most infectious diseases) is to avoid being exposed to the virus that causes the disease. Rather than taking nutritional supplements, herbal remedies, or treatments, follow the Centers for Disease Control and Prevention (CDC) recommendations to wear a mask over the nose and mouth in public, and to avoid touching the face with unwashed hands. The CDC also recommends avoiding contact with people who have COVID-19 and to practice social distancing.

The only scientifically proven interventions to boost the immune system are to eat a nutritious diet rich in fruits and vegetables, get adequate sleep, exercise regularly, and manage your stress. A number of companies, wellness enthusiasts, celebrities, TV personalities, and social media influencers have preyed on public anxiety and fears during the COVID-19 pandemic. The FDA and Federal Trade Commission have sent letters to many companies warning them to stop advertising fraudulent therapies to prevent or treat COVID-19 (FDA Office of Regulatory Affairs, 2021). Although these federal agencies make their best efforts to monitor websites and social media platforms to identify fraudulent claims, at the end of the day it is our responsibility as consumers to make informed decisions. This means relying on high-quality scientific evidence. It is important to critically examine, investigate, and research claims before taking nutritional supplements or sharing these suggestions with others.


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