Debunking fake news about the use of plants or plant derived compounds in the treatment or prevention of SARS-CoV-2 infection

We are living in challenging times. In times like these, everyone is under pressure, feeling lost and confused. Nevertheless, we crave good news. We want to hear that the death toll is decreasing and that we managed to flatten the curve, dreaming about going back to “normality” (for whatever that means). Many of us are scrutinising the news, trying to find out if researchers found a treatment or, even better, a vaccine against the virus that has turned our lives completely upside down.
In such a scenario, if somebody is telling us “Hey, look, this seems to work”, we might want to believe it. No matter how bizarre it sounds.
Here, two additional important actors of these modern times come on stage: internet and social media. Lucky us to have them right now! Could you imagine facing weeks of lockdown without them? However, these tools also have their downside; anything posted there can spread very fast, no matter the quality or even the truth and reliability of what is reported.

This is how our friend learned that garlic is great against COVID-19 or he heard another one of the countless fake news stories gone viral. The myths are so many and so widely spread that the World Health Organization had to dedicate a section of its website to disprove them (https://www.who.int/emergencies/diseases/novel-coronavirus-2019/advice-for-public/myth-busters). They range from the sci-fi plot in which the 5G technology seems to be involved in spreading the virus to dangerous practices like using chlorine spraying on the entire body for disinfection. The list is very long and continuously updated. However, myths need to gain a worldwide popularity to make it to the list and, unfortunately, they are way more than the ones reported there. A lot of them are related to the use of plants (or their parts) and natural products to treat either the symptoms of COVID-19 or even acting directly on the virus SARS-CoV-2. a In the next paragraphs we will go through the most popular ones and we will see why we should not believe them.


Top 3: garlic, oranges and vitamin C

Let’s start with the most popular presumed natural remedy against COVID-19, the one that made it to the WHO list: garlic. Used since ancient times as a spice and as a traditional medicine, Allium sativum is rich in several interesting bioactive compounds. The properties, the smell and the taste of garlic are attributed mainly to sulphur containing compounds (among which alliin, allicin, ajoene, etc.).b Some of these metabolites are reported to be antioxidant, antimicrobial, anticancer, cardioprotective, antithrombotic, anti-inflammatory, etc. with a good body of scientific literature for many of these properties (1, 2, 3).
However, it needs to be clear that in some instances we are talking about activities that have only been tested in vitro or at best in animal models. Therefore, in those cases we should be very careful when translating this to human health!
Despite the large amount of studies on garlic and derived compounds, there are very few studies about their antiviral action as well as about the role in the prevention or protection from viral infection (3). On the other hand, a study aimed at determining whether garlic is effective for the prevention or treatment of the common coldc showed that there is insufficient clinical trial evidence regarding the effects of garlic in preventing or treating it (4).There is, finally, no study on the effects against SARS-CoV-2. This means that currently there is no scientific evidence supporting the use against COVID-19 of garlic and products or chemicals derived from it.

For those of us that do not like the smell or taste of garlic, don’t worry! There is a nicer smelling approach. A method that seems to be very popular is to breath the steam generating from boiling water containing orange or lemon peels with either salt or cayenne pepper (depending on the recipe). This is supposed to avoid the virus from entering the body or to help you get rid of the mucus, because “there is where the virus lives” (cit.).d Well, let’s first clarify that, if anything, the mucus is a defence mechanism of our body, but I won’t go into the details of this now. Going back to the treatment, it is even hard trying to imagine where this belief came from. With the steam generating from boiling the peels of these citrus fruits, one might get a nicely smelling kitchen, maybe some face pore cleansing, but probably nothing more. By heating up orange (or lemon) peels, we are increasing the evaporation of some compounds (mainly limonene, but not only). Well, by boiling them in water, we are also extracting other compounds, but not using them since the only thing that we are doing is inhaling the vapours. There are some studies reporting the antiviral activity of some of the volatiles that are also found in oranges or lemons, but they usually refer to mixtures (that are hard to reproduce). Furthermore, the amounts used in these studies are far too high to support the validity of this method. So, not only it won’t work the way it is supposed to, but we also have to say that there is no evidence for possible other ways it could help.

The last, in our top 3, is not a plant (or part of a plant), but it is a chemical, i.e. vitamin C (or ascorbic acid), very abundant in several fruits and vegetables. This compound is a powerful antioxidant (5), meaning that it can protect cells from the damage caused by an oxidative imbalance. It is also involved in several biochemical processes, by acting as a cofactor of numerous enzymes, and it has been shown to influence the immune response (by enhancing the activity of phagocytese and possibly promoting the differentiation and proliferation of lymphocytese 6). Despite these important roles, there are also some myths related to its consumption. I bet that you have often been told to consume more vitamin C to prevent cold. Well, from the studies carried out so far, we can infer that vitamin C does not make you any less likely to get a cold, but it only seems to favour a (slightly) faster recovery (7).
It must be said that there are very few and highly controversial and debated studies about its activity against the inflammation induced by some viruses causing severe respiratory illness, but these are mainly case-reports and studies on animal models (with all the consequent limitations). Very debated are also the reports on the hypothetical use in patients with severe cases of sepsis. Perhaps, these studies inspired an ongoing study in China, using high IV doses of vitamin C in severely ill patients affected by COVID-19. The results of the study are not known yet.
So far, there is no evidence for any role of this vitamin neither in the treatment, nor in the prevention of the SARS-CoV-2 infection. Please also note that there is no way to take the high suggested doses orally (the excess is excreted).

What about other herbal remedies?

Herbal remedies, especially some of them, seem to be the panacea for nearly everything.
Despite the attempts of different organizations and authorities to avoid the spread of misinformation, many websites are presenting, even disguised as science-based statements, a list of herbs or herbal remedies that can supposedly either support the immune system (e.g. cinnamon, liquorice, Astragalus membranaceous, rosemary, thymian, sage, echinacea, etc.) or act as antiviral (e.g. aloe, Houttuynia cordata, Nigella sativa, Sambucus nigra, Cistus incanus, Artemisia annua, lemon balm, St. John’s wort, etc.) or finally treat the symptoms, like inflammation or fever (e.g. Scutellaria baicalensis, ginger, elderberry, goldenseal, turmeric, etc.). Needless to say, these lists reported above are not exhaustive!
Noteworthy, some of these herbs are said to have more than one of the cited properties (sometimes all of them).
Well, I have to say that for a few of them there is some evidence of some kind of activity related to the mentioned ones. However, there are many points to make here. Above all, we still ignore a lot about this virus, including if any of the aforementioned plants or their active principles are really effective. It is every day clearer that even regarding the symptomatology there are points that are still obscure. Therefore, we have no idea yet of what is the best way to deal with it.
Another important point is more general about herbal remedies and is related to the high variability in the content of active principles, not to mention the possible side effects or the co-occurrence of toxic compounds (heads up: natural does not by any chance mean safe).f

Last, but not least: wine

Let’s end our (surely incomplete) survey with another evergreen, which in this case is not a plant, but the product of the fermentation process of grapes, i.e. wine. This is also often indicated as an alleged treatment for several diseases. Especially red wine, whose properties have been long claimed after the discovery of resveratrol, which indeed has some interesting properties (8), although many of them still need to be further explored. Nevertheless, so far there is no evidence that resveratrol could in any way help preventing or treating any symptom of COVID-19. There are a few studies on its antiviral activity, including against MERS-CoV virus, but these studies are very preliminary, reporting only in vitro experiments.


Is there any plant derived option against Covid-19?

Based on what we have discussed so far, is there any chance for plants and natural products to help fighting this virus? Well, the answer is “maybe”. There are a few natural products that are currently being tested for their activity, in studies aimed at understanding if they could be used either to treat the symptoms of Covid-19 or against the virus. There are ongoing experiments and trials at different levels, and we all hope we will have good news.
Right now, there is no proved and approved treatment against the virus or the symptoms.
The only thing that really works is prevention by physical distancing and applying all the WHO suggestions, above all hand washing!

How can we help stopping the spreading of fake news?

We know how to mitigate the spread of the virus, but we also know how to avoid the dissemination of fake news.
The recommendation for everybody is to never passively believe what is shared on social media but checking for the sources. If there is a scientific study to back up what is claimed, then this is a good starting point. However, I also suggest you to always ask somebody that has the expertise to read and critically assess the scientific literature. For many reasons. On one side, science is a continuous process. Therefore, we are always looking at only one limited aspect within the bigger picture. This detail is still important to understand the phenomenon we are studying, but it can be misleading if taken per se. This means that we have to be able to understand, for example, that an in vitro study is very important, as it paves the way for further studies, but it is just an in vitro study and as such should be read, just to mention an example. Furthermore, the more we get to learn about a phenomenon, the better we can understand it: this might also mean to have to reconsider previous interpretation of data in light of the latest discoveries.
Unfortunately, we also have to consider that not all the scientific literature is always responding to the required criteria. And here comes an appeal to the people working in the field, to stick to the principles of good scientific practice and research integrity, in order not to give fake hopes to people (besides other very important reasons to do it). This is not the time for getting an easy publication, but it is a great time to join our efforts to face the challenge we are dealing with, each one with our own expertise.


Notes
a. COVID-19 is the name of the disease caused by the virus SARS-CoV-2.
b. A detailed discussion about garlic and its bioactive compounds would be too long to address here. However, it will surely be the topic of future posts.
c. The common cold is a heterogenous group of diseases caused by several viruses belonging to different families (i.e. picornaviruses-rhinoviruses and enteroviruses-,coronaviruses, adenoviruses, parainfluenza viruses, influenza viruses, metapneumoviruses and respiratory syncytial viruses).
d. Scientifically unsound and not shared by the author of this post.
e. These are both cell types belonging to the immune system.
f. This topic should be further developed and will be addressed in future posts.

Aknowledgments: I would like to aknowledge those who have notified me about some of the fake news discussed here, in particular Dr. Eugenio Boccalone, Dr. Mohèb Elwakiel and Prof. Antonio Fiorentino.

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