The best defense against ANY virus is a healthy immune system

Author: Dr. Michelle Durkin on 21 April 2020

Now, more than ever, is the time to have the strongest immune system you can possibly have. And the nutrients we need for a strong immune system come from healthy, whole, unprocessed foods.

Did you know that one tablespoon of sugar (or 15 grams) will depress your immune system for twenty minutes?

Did you know that your beloved low-fat vanilla yogurt has 33 grams of sugar per cup?

Your "healthy snack" Cliff bar has 22 grams of sugar per bar?

Your doughnut alternative, a Tim Horton's bran muffin, has 37 grams of sugar per muffin?

You need the right information to make good decisions about your health.

That is why this year's spring 10 Day Healthy Body, Healthy Detox is going to have an immune focus. If you are subscribed to my newsletter look for your invitation later this month.

In preparation for this detox I would like to highlight a few key nutrients for your immune system, and the foods that you can find them in. These nutrients, along with sufficient sleep and stress management, will help you create a strong immune system now and forever.

All the recipes in this spring's detox will be focused on increasing these nutrients in your diet.

Let's dive in!

Vitamin C:

Vitamin C is known to help reduce common cold symptoms. It can shorten the duration of cold symptoms, as well as the severity of those symptoms. Vitamin C supports various cellular functions of both the innate and adaptive immune system. Vitamin C accumulates in phagocytic cells, such as neutrophils, and can enhance chemotaxis, phagocytosis, generation of reactive oxygen species, and ultimately microbial killing. Supplementation with vitamin C appears to be able to both prevent and treat respiratory and systemic infections. Higher doses of Vitamin C during an illness can also act as a natural antihistamine and anti-inflammatory. Vitamin C can be found in many fresh fruits and vegetables, including red peppers, broccoli and spinach, to name a few.

  • Hemilä H. Vitamin C and infections. Nutrients. 2017;9(4):E339. doi:10.3390/nu9040339
  • Rondanelli M, Miccono A, Lamburghini S, et al. Self-care for common colds: the pivotal role of vitamin D, vitamin C, zinc, and echinacea in three main immune interactive clusters (physical barriers, innate and adaptive immunity) involved during an episode of common colds—practical advice on dosages and on the time to take these nutrients/botanicals in order to prevent or treat common colds. Evid Based Complement Alternat Med. 2018;2018:5813095. doi:10.1155/2018/5813095


Zinc is another major player in building up our immune system and foods are often overlooked as a great place to find zinc. It is essential for many cellular functions, including our white blood cells, especially in times of stress. There is also evidence that it suppresses viral attachment and replication. Oysters are a well-known source of zinc, as is red meat. If you’re looking for plant-based sources, chickpeas and almonds are also a great source.

  • Prasad AS. Zinc is an antioxidant and anti-inflammatory agent: its role in human health. Front Nutr. 2014;1:14. doi:10.3389/fnut.2014.00014
  • Hulisz D. Efficacy of zinc against common cold viruses: an overview. J Am Pharm Assoc (2003). 2004;44(5):594-603. doi:10.1331/1544-3191.44.5.594.hulisz
  • Meydani SN, Barnett JB, Dallal GE, et al. Serum zinc and pneumonia in nursing home elderly. Am J Clin Nutr. 2007;86(4):1167-1173. doi:10.1093/ajcn/86.4.1167
  • Barnett JB, Dao MC, Hamer DH, et al. Effect of zinc supplementation on serum zinc concentration and T cell proliferation in nursing home elderly: a randomized, double-blind, placebo-controlled trial. Am J Clin Nutr. 2016;103(3):942-951. doi:10.3945/ajcn.115.115188
  • Maares M, Haase H. Zinc and immunity: an essential interrelation. Arch Biochem Biophys. 2016;611:58-65. doi:10.1016/

Vitamin D:

Vitamin D is known as the sunshine vitamin, and for good reason! The sun is the best way to get vitamin D. Throughout the winter months, and due to social distancing right now, you may be spending less and less time outside, so it’s best to find ways to increase vitamin D through food. Vitamin D is an immune system modulator that reduces the expression of inflammatory cytokines and increases macrophage function. Vitamin D also stimulates the expression of potent antimicrobial peptides (AMPs), which exist in neutrophils, monocytes, natural killer cells, and epithelial cells of the respiratory tract. Insufficient vitamin D is linked to impaired immune function. Foods that are a great source of vitamin D are liver, mushrooms, egg yolks and fatty fish.

  • Martineau AR, Jolliffe DA, Greenberg L, et al. Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis. Health Technol Assess. 2019;23(2):1-44. doi:10.3310/hta23020
  • Hewison M. Vitamin D and immune function: an overview. Proc Nutr Soc. 2012;71(1):50-61. doi:10.1017/S0029665111001650
  • Zdrenghea MT, Makrinioti H, Bagacean C, Bush A, Johnston SL, Stanciu LA. Vitamin D modulation of innate immune responses to respiratory viral infections. Rev Med Virol. 2017;27(1). doi:10.1002/rmv.1909
  • Sluyter JD, Camargo CA, Waayer D, et al. Effect of monthly, high-dose, long-term vitamin D on lung function: a randomized controlled trial. Nutrients. 2017;9(12):E1353. doi:10.3390/nu9121353
  • Bergman P, Lindh AU, Björkhem-Bergman L, Lindh JD. Vitamin D and respiratory tract infections: a systematic review and meta-analysis of randomized controlled trials. PLoS One. 2013;8(6):e65835. doi:10.1371/journal.pone.0065835


Garlic is often a vegetable that goes unnoticed when it comes to building up immune response. It’s one of the oldest remedies across many different cultures to help the immune system. It contains many different compounds that can influence immunity. Studies have shown that both fresh garlic as well as aged garlic extract may reduce viral upper respiratory infection severity as well as function in the prevention of infection with viruses that can cause colds. And there are so many different ways to use it in recipes!

  • Josling P. Preventing the common cold with a garlic supplement: a double-blind, placebo-controlled survey. Adv Ther. 2001;18(4):189-193. doi:10.1007/bf02850113
  • Nantz MP, Rowe CA, Muller CE, Creasy RA, Stanilka JM, Percival SS. Supplementation with aged garlic extract improves both NK and ??-T cell function and reduces the severity of cold and flu symptoms: a randomized, double-blind, placebo-controlled nutrition intervention. Clin Nutr. 2012;31(3):337-344. doi:10.1016/j.clnu.2011.11.019
  • Percival SS. Aged garlic extract modifies human immunity. J Nutr. 2016;146(2):433S-436S. doi:10.3945/jn.115.210427


By now, we all know the positive effects that probiotics can have on our gut function, but they can also help our immune response. In fact, specific probiotic strains help reduce upper respiratory tract infections in the elderly. 

  • Hojsak I, Abdovi S, Szajewska H, Milosevi M, Krznari Z, Kolacek S. Lactobacillus GG in the prevention of nosocomial gastrointestinal and respiratory tract infections. Pediatrics. 2010;125(5):e1171-e1177. doi:10.1542/peds.2009-2568
  • Wang Y, Li X, Ge T, et al. Probiotics for prevention and treatment of respiratory tract infections in children: a systematic review and meta-analysis of randomized controlled trials. Medicine (Baltimore). 2016;95(31):e4509. doi:10.1097/MD.0000000000004509

Now I would love to hear from you! What is your favourite immune boosting food? Leave a comment below and I'll be back next week with another edition of Doctor as Teacher Tuesday!

This post is only intended to identify modalities that may help your immune system, not coronavirus specifically. It is not meant to recommend any treatments, nor have any of these modalities been proven effective against coronavirus. Always consult your physician or healthcare provider prior to using any of these modalities. 

3 Replies to “The best defense against ANY virus is a healthy immune system”


Excellent article – especially on sugar!

Andy Burke

Thank you for those interesting articles. I usually get frustrated with these articles because I am constantly being told to watch my intake of foods containing virus C; phosphorus; calcium, potassium & metals such as zinc. In fact I don’t know what to eat or drink anymore. The treatment 4 my disease is to suppress the immune system

Dr Michelle Durkin ND

Thanks for your comment Andy. The great thing about nutrients is that they are beneficial to the immune system regardless if your immune system is under-reacting OR over-reacting. For a personalized recommendation please check with your Naturopathic Doctor.

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