This program was funded by a grant from the Community Radio Fund of Canada and the Government of Canada’s Local Journalism Initiative

Around the globe, people are dealing as best they can with the novel coronavirus outbreak, SARS-CoV-2, also known as COVID 19. 

After we wash our hands, don a facemask and avoid non-essential travel and socialization – many of us are looking for ways to maximize our immune function.  

A quick internet search will reveal an assortment of advice on what diet, lifestyle and supplements may increase your resistance to contracting the virus, and your resilience to illness if you do. 

Photo credit: Chantrelle jackpot by Suzanne LaGasa via Flickr (CC BY SA, 2.0 License)
Cortes Currents: Max Thaysen interviews Drs. Phillip Calder and Jenna Creaser about lifestyle and supplements that can strengthen your immune system

Stressing foods, lifestyle and supplements – Pseudoscience? Or much more?

But there are internet resources that say the opposite – supplements are unproven and those peddling them are pseudoscientists. 

Cortes Currents sought to shed light on the importance of the immune system and how we can support it.  

We connected with Dr Jenna Creaser from the Cortes Community Health Centre and Dr Philip Calder.  

Professor Phillip Calder

Professor Philip Calder is Head of Human Development & Health and Professor of Nutritional Immunology within Medicine at the University of Southampton.  He has a chair in Nutritional Immunology, his area of expertise.  

His work has mostly been with omega-3 fatty acids, but has also researched pre-biotics and pro-biotics (the beneficial organisms we rely on and the conditions that support them).

He authored the paper Nutrition, Immunity and COVID-19which was published in the British Medical Journal – Nutrition, Prevention & Health. 

He also co-authored Optimal Nutritional Status for a Well-Functioning Immune System Is an Important Factor to Protect against Viral Infectionswhich was published in the journal MDPI Nutrients.This is where he first caught our attention.

Healthy Diets

We asked Professor Calder:  how does a healthy diet contribute to the immune system?

He said that we know that our body relies on the intake of micro-nutrients for normal functioning of all systems including our immune systems.  And the reverse is also true: deficiencies in some micro-nutrients results in increased susceptibility to illness, noting especially respiratory tract infections.  And  the evidence suggests that increasing the levels of micro-nutrients in deficient individuals can increase markers of immune function. 

Calder goes on to point out that the vast majority of people who contract COVID-19 are asymptomatic – and this indicates that our immune systems are ‘doing reasonably well’.  

Professor Calder, along with his co-authors in the paper for MDPI Nutrients, claim that, “a wealth of mechanistic and clincal data” suggest that many nutrients that are critical to proper immune function, and that, “inadequate intake and status of these nutrients are widespread”.

Our immune system 

And how does our immune system contribute our interactions with the virus that causes COVID-19?

He says that individuals most at risk of serious illness from COVID-19 are those who, for various reasons, have depressed immune systems and association studies have shown a correlation between outcomes and Vitamin D, Selenium and Zinc deficiencies.  He points out that these are associations, and not randomized control trials. 

Local family physician, Dr Jenna Creaser, agrees that a healthy diet supports a healthy immune system, and “makes a huge impact on people’s health”.  She says more and more doctors are realizing this.

She says that a varied diet, with lots of fruit and vegetables supports our body’s system, including the immune system. And more and more doctors are turning to diet to prevent and treat illnness.

Vitamin D

What potential impact might diet have on COVID-19 prevention and treatment?

Professor Calder describes the association studies that have been done with micro-nutrients.  The studies looking at Vitamin D found that deficiency in this nutrient correlated with a 30% increase in hospitalization.  Calder adds that there could be other factors that come along with Vitamin D deficiency, and the effect sizes might not be so large. 

So there appears to be a reasonable basis for a strong message that implores people to attend carefully to their diet. 

What do Health Canada or the BCCDC say?

We are constantly reminded in the bustling COVID-19 information landscape to rely on Health Agencies for guidance.  And so what is the position of the BC Centre for Disease Control (BCCDC) and Health Canada on the role of diet in battling the pandemic?

It is hard to say.

The COVID-19 page at, COVID-19 for the public, does not mention healthy eating or supplements.

The COVID-19 page at has a section called ‘Your Health’, and a page on prevention and risk – with no mention of diet or lifestyle. 

I was able to find, in another part of Health Canada’s website, the nutrition section, some messages about diet: 

Simple, stand-alone sentences:

  • “You can eat a variety of healthy foods every day to feel good and maintain your health, even during the COVID-19 pandemic.” 
  • “Healthy eating is a good habit to keep up or start during this time.” 
  • “Although a healthy eating pattern is important for your overall health, there are no specific foods or supplements that can prevent you from catching COVID-19.”

And the page goes on to recommend the standard healthy-diet fare. 

Declined to clarify

Cortes Currents requested clarity on these statements from Health Canada – they seem to neither confirm nor deny the role of diet in prevention of disease or reduction of its severity.

They declined to clarify their position, and declined to be interviewed for this show. But stated that that Health Canada is considering linking their nutritional page to the COVID-19 page.  

Clinical data for Vitamin D

A dietician with HealthLinkBC shared some deeper insights into the Health Canada position.  She read from a document she had received from them:

“Vitamin D plays various roles in the body… including reduction of influenza.  There is insufficient evidence suggesting cause-and-effect for outcomes, other than bone health…. In the absence of randomized clinical trials, Health Canada cannot attribute any role or benefit of vitamin D supplementation as a measure to enhance resistance to COVID-19.”

Professor Calder agrees – there are no completed Randomized Clinical Trials (RTCs) treating COVID-19 with Vitamin D though they are underway, he says.   Regardless, he’s more interested in prevention and supporting the immune system prior to infection. 

Dr Creaser adds that while RCTs are considered the gold-standard for proving an effect, they can be very hard to do.  

Clinical data for fruit and veggies

Professor Calder offers one example where an RCT was done comparing the effect of increasing fruit and vegetable consumption – it yielded a result of inceased markers of immune function. 

Dr Creaser goes on to say that there should be a role for common sense and extrapolating from all that we do know about the importance of diet to our health and applying that to COVID-19.

Possible risk from a ‘healthier’ diet

Any action taken in healthcare, must weigh costs or risks, against benefits.  What are the risks associated with promoting healthy eating and supplementation?

Calder says that he isn’t talking about high dose treatments, but nutritionally relevant doses for prevention. 

Creaser has a hard time thinking of what the costs might be to reinforcing healthy eating habits.  “I don’t see why, with the amount of messaging that has come out, … there couldn’t be more on these measures to be more healthy in general… and not only with COVID, but with anything.”

Possible benefits of a healthy diet

Dr Creaser alludes to other potential health benefits.  What are the potential beneficial side-effects of this type of messaging, beyond our personal COVID-19 outcomes?

Professor Calder explains that our immune system tries to stop viruses from having a place to live and reproduce.  “If the immune system gets the upper hand… transmission will go down, because viral load will go down.”

“We have a society with a lot of other disease,” Dr Creaser points out.  “A pandemic of heart disease, a pandemic of obesity, a pandemic of stress… a huge part of that is diet and lifestyle.”

Calder agrees, “The same healthy eating advice applies to cardiovascular disease, to cancer, to diabetes, and so on… the big sources of morbidity and mortality.”


Another benefit of maximizing immune systems, Calder says, is that it maximizes vaccine effectiveness.  He says, “the vaccine is an immune challenge, and it works by triggering an immune response.  And we need that response to be optimized.”

And, while it may sound like a silver bullet – Professor Calder points out that there is still death from influenza, despite having vaccinations for that.  “Therefore, helping the immune system out makes some sense.”

Why aren’t we hearing more about diet?

So, with so much, potentially, to gain and little in sight to lose – why is there such sparse public health advice to focus on our diet?

Professor Calder believes that the health authorities may simply have a higher standard of evidence than that which may be warranted.  

“We don’t have … COVID-19 specific evidence at the level that the health authorities would want to make a statement,” he says. 

Dr Creaser comments that even before the pandemic, our healthcare ignored preventative measures, stating, “I truly feel like our healthcare system, doesn’t ignore, but, looks at it in a very bare minimum type fashion.”

Calder points out that, in the management of cardiovascular disease, dietary treatments exist alongside drug and surgical therapies – so the pairing does have precedent.  Though in the treatment of infectious disease, he says, “that seems to be … one step too far maybe.”

When he recalls the progression of the medical response to the pandemic, Calder notices that the response was dominated by anti-retroviral testing, and vaccine development and off-label drug use. “The emphasis hasn’t been an inappropriate one, but I think an emphasis on lifestyle, including diet, have been made”, he said. 

Professor Calder describes three aspects to the response in the UK that demonstrate that there is room for advocating for a dietary response to COVID-19.  

Go outside to get exercise

First, the UK government acknowledged that despite restrictive lockdowns, it was necessary that people got outside to exercise, for their general health, despite potential increased risk of transmission.

Second, in the UK, health authorities recognized that with people spending more time indoors due to lockdowns, they would be getting less vitamin D from the sun and promoted supplementation – not for COVID-19 mitigation effects, but for general health and bone health. 

And third, the UK Health authorities did take seriously evidence of an association between COVID-19 and obesity.   They began an intensive program to promote weight loss, using TV ads, billboards and posters to spread the message.  

Professor Calder concludes: these pandemic response measures demonstrate the kind of thinking and messaging that he would like see applied to diet. 

Want to be taken seriously

Dr Creaser offers another theory to explain the missing health advice: 

“Some healthcare workers or decision makers are concerned people won’t take it seriously if they think they’re healthy because they’re eating a certain way.  But I think that’s a false assumption.”

Calder thinks that could be part of the explaination —  authorities don’t want to be seen to be telling people “if you do this, you won’t catch COVID-19”. 

But the message could be carefully crafted – Calder suggests, “you don’t have to say it’s the answer to the problem.”

Dr Jenna Creaser – courtesy Rising Rose Wellness website

Not making claims too early

Dr Creaser offers up another theory – she recounts how a recent version of the Canada Food Guide was met with some resistance from health experts.  Health Canada was gracious and made some changes to better reflect the science.  But perhaps that sort of institutional hazard, of making claims too early before the dust has settled on the science, could contribute to reluctance to suggest that perhaps diet is important to immune function. 

Dr Creaser suggests that the fast paced scientific changes, might make authorities slow to promote options – “because maybe it won’t be the most correct… thing”, she says.

Food First

But Professor Calder is quick to calm that concern as well.  He says, “we don’t need more evidence for the ‘healthy eating’ message, not reinforcing that message has been something that’s been missing.”

So, what should that message be?

“Food first”, Dr Creaser offers.  


Both recommend a diverse diet with plenty of different and colorful vegetables and protein.

Both recommend supplementing with Vitamin D, especially in the winter.  Creaser suggests 2000 IU/day seems to have the most evidence in support.

Dr Creaser also recommends garlic, ginger and mushrooms, the latter being a whole kingdom worthy of its own exploratory article or book.

Creaser says hydration is important.  Zinc shows benefits for immune function (25-50mg/day for most people.  And people can consider Elderberry and vitamin C, probiotic and prebiotic foods (she’s not so sure on the evidence for probiotic supplements).

And Creaser says that people should have some form of regular practice such as walking in nature, meditation or yoga.

“It seems so obvious, when I say it.  So I hope that’s helpful”, Dr Creaser says.

So, there you have it.  There’s the missing message.  Choose food.  Take a breather.  And supplement as needed.  

Many thanks to Dr Jenna Creaser and Professor Philip Calder for taking the time to share their insights and expertise.  For more information, you can find links to the studies in the article for this piece on  You can speak with a dietician for nutritional guidance by calling 811. 

Dr Creaser recommends checking out for more immune supporting diet and supplement advice. 

Links of interest:

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Top photo credit: Taken during a cold and foggy winters day through the Lickey Hills, in the UK, by Adam Hinett via Flickr (CC BY SA, 2.0 License)