This article was written by Dietetically Speaking’s intern Zachary Wenger.
COVID-19 is a respiratory illness that can spread from person to person.
Key steps for reducing the risk of catching COVID-19:
- Avoid close contact with people who are sick
- Avoid touching your eyes, nose, and mouth with unwashed hands.
- Wash your hands often with soap and water for at least 20 seconds.
- Use an alcohol-based hand sanitizer that contains at least 60% alcohol if soap and water are not available (1).
However, across social media we’ve heard that a variety of methods including juicing, apple cider vinegar, elderberries, and even the ketogenic diet can “boost our immune system” and combat against COVID-19.
This article will explain why there are no single foods or supplements that will prevent or cure COVID-19, and debunk recent diet claims related to this.
‘Immune Boosting’ Claims
Before we dive into these specific foods and supplements, how does our immune system defend our body? The immune system is designed to implement rapid, specific, and protective responses against foreign invaders, called pathogens (2).
The term “boosted immune system” is unscientific and is often used in clickbait headlines and marketing.
Dietary choices don’t boost the immune system, rather it can allow the immune system to function adequately and more efficiently.
Let’s say theoretically that we could boost our immune system’s activity through diet. That would not be a good thing. An overactive system or even an underactive immune system can both lead to negative immunological responses.
An example of an unwanted ‘boosted’ immune system are autoimmune diseases. An autoimmune disease is a condition in which our own immune system attacks our cells, tissues, and/or organs mistakenly. For example, the skin disorder, psoriasis occurs when overactive immune system cells collect in the skin causing scaling on the skin’s surface (3).
Other diseases that are caused by a boosted immune system include type 1 diabetes, rheumatoid arthritis, lupus, inflammatory bowel disease, and many more.
We don’t want an overactive or underactive immune system.
Instead, we would want to support our current immune system with an overall healthy diet and lifestyle. For example, a balanced diet provides a range of nutrients which play an important role in our immune system, such as: vitamin A, vitamin D, vitamin C, vitamin B6, vitamin B12, zinc, folate, iron, selenium and copper (4).
Vitamin C is required in the body to act as a cofactor to synthesize collagen, to act as an antioxidant, along with other vital tasks (5-6). Vitamin C is found in a variety of plants including bell peppers, strawberries, oranges, mangos, broccoli and kale.
There is no question that vitamin C plays a role in the immune system, however the research has found that vitamin C supplementation does not reduce the risk of the common cold in the general population (7).
However, vitamin C may be beneficial for those exposed to periods of severe physical exercise. A systematic review from found 2013 “In five trials with 598 participants exposed to short periods of extreme physical stress (including marathon runners and skiers) vitamin C halved the common cold risk” (7).
While vitamin C supplementation did not reduce the incidence of the cold, it did reduce the duration of the cold. In adults the duration of colds was reduced by 8% and in children, 1 to 2 g/day vitamin C shortened colds by 18% (7). In real terms, this works out as reducing a cold by half a day to one day.
It is also important to note that more vitamin C does not necessarily mean better. The recommended dietary allowance (RDA) in the US is set at 90 mg/day for men and 75 mg/day for women, whereas the European population reference intake (PRI) is 110mg per day for adults. Excess vitamin C is eliminated in the urine and may also cause uncomfortable symptoms including nausea, abdominal cramps, diarrhoea, headache, fatigue, and a possible increased risk of forming kidney stones (8-9).
A study in China which is looking at the impact of high dose vitamin C administration via IV drip (10). But the results are not published yet.
So it is too early to make any claims related to vitamin C in the treatment of COVID-19; beyond maintaining adequate vitamin C to support the healthy function of our immune system.
Elderberries are fruit from the Sambucus tree. Many individuals are claiming that elderberries can ‘boost’ our immune system — which we already know is poor terminology, as foods don’t operate that way and we wouldn’t want our immune system boosted.
Most of the research has been done in labs or in animals and there are very few human trials.
Researchers investigated elderberry supplementation on symptoms such as cold episodes and cold durations. The participants in this trial were those on intercontinental flights, as air travel often causes stress. Elderberry supplementation did not show statistically significant reductions in the incidence of the cold in this trial. However, there was a statistically significant reduction in the duration of the cold to those that had it (11).
We need to keep in mind that while the results are interesting, this cannot be equated to simply anyone catching the cold. These individuals experienced long haul intercontinental flights, time zone adjustments, and climate change. The researchers excluded those suffering from allergies, respiratory diseases, immune disorders, or those pregnant/trying to get pregnant. These findings apply to a very broad spectrum of the population.
A meta-analysis of randomized controlled trials investigated the relationship between elderberry supplementation on upper respiratory symptoms (12). The researchers concluded that elderberry supplementation substantially reduced upper respiratory symptoms. While the effect was consistent and repeated, the meta-analysis only included 180 participants.
The results from the limited trials we have available are indeed promising, but we would need more rigorous and long term human data to make accurate recommendations.
So although it won’t do any harm to include elderberries in your diet, this should not be promoted as a cure or treatment for COVID-19.
Echinacea is a popular supplement or herb which people commonly take to help fight against the flu or colds. It’s a plant whose roots and leaves have been traditionally used for medicinal purposes.
The largest randomized controlled trial to date investigating the relationship between echinacea and the common cold found that illness duration and severity was not statistically significant compared to placebo (13).
There is also a well-designed systematic review of randomized controlled trials investigating the same relationship. The researchers investigated twenty-four double-blind trials with 4631 participants and concluded that echinacea products didn’t provide significant benefits for treating colds. However, they found that it’s possible that there may be a weak benefit. (14).
Overall, there is currently no convincing evidence that taking echinacea helps in the prevention or treatment of colds or flus.
The idea that juicing “boosts the immune system” and “cleanses the body” may be one of the most popular claims. Examples include: celery juice or a mix of different juiced fruits and vegetables.
While juicing removes nearly all of the fibre and potential reductions in vitamin C and calcium, juicing still provides essential minerals and nutrients (16).
One of the only trials published to date on the respected topic investigated the relationship between fruit juice consumption and a variety of different biomarkers, which included immunity biomarkers in 27 healthy men (17). The researchers concluded that the fruit juice enhanced antioxidant status, reduced DNA damage, and stimulated immune cell functions.
Whole fruits and vegetables have been much more studied in all aspects of health.
For example, consuming 7-10 portions of fruit and vegetables per day is associated with a lower risk of heart disease, cancer and an early death (18).
Consuming at least 5 portions of fruit per day has also been associated with improvements in immune response in older adults, although there isn’t as much evidence related to this (19).
So consuming 5-10 portions of fruit and vegetables per day is undoubtedly important for our overall health, as well as the functioning of our immune system.
But we would specifically need to see human outcome data for those same fruits and vegetables juiced. Furthermore, 150ml of juice only counts as one portion of fruit or vegetables once per day, regardless of how much you consume.
Apple Cider Vinegar
Apple cider vinegar has been used for centuries as a home remedy for immunity. It is made by mixing yeast with crushed apples and the yeast converts the sugar into alcohol. This is a biochemical process called alcoholic fermentation.
Surprisingly, there hasn’t been any human trials examining the relationship between apple cider vinegar and our immune system. The best data we have is a study which tested apple cider vinegar in petri dishes – this found that apple cider vinegar may kill microorganisms like bacteria (15).
In vitro experiments definitely have a significant role in research by describing mechanisms at a cellular level. However, it cannot replace findings in humans. There is a huge difference between finding microbial activity in a petri dish and killing microorganisms inside of our body.
There definitely is not enough evidence to promote the use of apple cider vinegar for supporting our immune system or as part of the management of COVID-19.
The alkaline diet is based on the unscientific premise that acid based foods which include meat, grains and fish generate acid buildup in the body, which causes a variety of different diseases and disorders.
Similar to apple cider vinegar, there isn’t much research at all. To be specific, there are no human trials, zero.
The theory behind the alkaline diet is a bit odd as cell and blood pH is tightly regulated at about 7.4 to sustain life. Eating acidic foods won’t change the pH of our blood. Eating alkalizing foods won’t change the pH of our blood.
The alkaline diet isn’t based on any available evidence and is simply based on a false theory. Therefore, there is no reason to follow this diet in relation to COVID-19.
Spirulina is a type of blue-green algae that is often touted by the media as a ‘superfood’. The claims surrounding spirulina are endless, immune boosting, detoxifies the body, curing allergies, and the list goes on.
In petri dishes and animal-based studies, spirulina looks excellent. Whereas, human trials tend to have a small sample size and often use sick populations or the elderly (20-23).
In the limited evidence we do have in humans, there is reason to believe it may be beneficial with symptom management in certain populations including those with allergies and nasal congestion.
Nevertheless, before we can start making any immune-related claims with spirulina, we would need stronger evidence than what we currently have.
Yes, you read that correctly, it made the list. Proponents of the keto diet claim that it could protect against the flu, and headlines have picked up on this. How did the media stumble upon this finding?
Researchers fed mice infected with influenza A, either a ketogenic or standard diet for seven days before infection. They found that after four days, the mice fed a ketogenic diet and infected with influenza A had a lower mortality rate than mice fed the standard diet (24).
The findings have been replicated in other trials using mouse models (25).
If I was a mouse, I would be all over the ketogenic diet. We just simply don’t have that level of research in humans yet.
Chicken broth, bone broth, and even vegetable broth have all been endorsed as good for the immune system.
For centuries now, chicken soup has been a home remedy for fighting against the cold. The most quoted study examining the relationship was an in vitro (performed outside of a living organism) experiment in which they found anti-inflammatory effects that may reduce the symptoms of upper respiratory tract infections (like colds, sinus infections and throat infections) (26).
The soup contained chicken, but also onions, sweet potato, parsnips, turnips, carrots, celery stems, parsley, salt, and pepper. The researchers found that all of the vegetables and the chicken individually had beneficial effects.
A 1978 trial also found that chicken soup was superior to hot water and cold water by possessing substances for increasing nasal mucus velocity (27).
The research surrounding broths, other than the studies I’ve mentioned, are extremely limited. While chicken broth has little evidence regarding immunity, vegetable broth and bone broth have even less. For bone broth, all we have are proposed mechanisms.
Currently, there isn’t a single trial investigating the relationship between bone or vegetable broth and immunity.
Before your favorite influencer suggests that you should be adding bone broth to your diet for it’s ‘immunity boosting’ properties, ask for evidence.
These diets have been promoting removing numerous foods from the diet, including: fats, eggs, dairy, gluten, corn, and much more. However, this is not backed by evidence.
In fact, by cutting out so many food groups we may actually reduce our intake of nutrients which are important for our immune system.
Genetically modified (GM) products such as corn, soya and canola (A.K.A. rapeseed) oil is also vilified by this diet. However, the largest meta-analysis ever conducted on GMO corn supported the cultivation, as it enhanced grain quality and reduction of human exposure to mycotoxins (toxic metabolites that can occur in corn) (28).
The World Health Organization (WHO) stated, “All genetically modified foods currently available on the international market have passed safety assessments and no effects on human health have been shown as a result of consuming genetically modified foods” (29). Check out this article for more information about GMOs.
The National Academy of Sciences stated, “Genetic engineering…poses no health risks that cannot also arise from conventional breeding and other methods used to create new foods” (30).
Overall, ‘antiviral diets’ are likely to do more harm than good by restricting overall nutrient intake.
Essential oils are a class of natural oils that represent the flavor and odor of the plant that it was extracted from. Individuals often regard essential oils as beneficial for the immune system because they supposedly have antimicrobial and antiviral properties.
Although these aren’t strictly diet related (they are usually inhaled or applied to the skin) we wanted to include them here as they are being promoted alongside various supplements at the moment.
The research does often point to aromatherapy potentially assisting in lowering anxiety and stress (31-32). However, it would be impossible to conduct the study blinded. In other words, is it really the essential oils lowering anxiety and stress or is it due to the person’s expectations with the oil? (A.K.A. the placebo effect).
In vitro studies have found potential benefits with essential oils in relation to our immune system (33-34). Unfortunately, these results have not replicated in humans. There aren’t any human trials investigating the relationship.
As I’ve stated previously, while these in vitro experiments are promising and interesting, it doesn’t mean that these same results will reoccur in the human body.
Therefore, be skeptical of anyone promoting essential oils for preventing or treating COVID-19.
COVID-19 is a scary time for most individuals. Largely because we don’t have much data on the disease as it’s brand new. In times like this, ‘diet gurus’ and zealots fill the gaps we have in science with speculation. Those that are fearful buy in. They eloquently and persuasively explain how X supplement will help “boost the immune system” which will then give you an extra layer of protection, in this case, from COVID-19.
Before we can make any reliable claims during this pandemic, we need repeated, robust, human clinical evidence.
As we saw, many of these foods and supplements that were claimed to be ‘immune boosting’ or a ‘superfood’, don’t have much scientific backing at all.
Next time you run out to buy a litre of apple cider vinegar, or hear anything that you know sounds too good to be true, ask the guru that recommended it for rigorous human evidence that supports their claims. Nearly each and every time, all that they have to offer are spurious anecdotes, animal models, or unproven mechanisms.
Evidence-based ways to support our immune system include:
- Consuming a balanced and varied diet
- Adequate sleep – most adults need 7 – 9 hours per night
- Staying physically activity (as able within current physical distancing guidelines)
- Regular thorough hand washing for at least 20 seconds
- Following the specific advice from the health authorities related to COVID-19, such as: physical distancing measures.
Stay evidence based and stay safe!
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