In this post I discuss and present nutrition-based strategies to strengthen your immune system, and the steps for the prevention and/or symptom relief of the flu and viral respiratory infections.

There are many helpful nutrients that are beneficial for the immune system that are talked about these days. However, in my clinical experience zinc, vitamin D, vitamin C, quercetin and probiotics are at the top of my immune ‘must have’ list. Also, zinc, vitamin C and quercetin work together compounding their immune enhancing actions.

These 4 key immune supporting nutrients plus probiotics discussed here, as well as accompanied lifestyle modifications, can be easily and effectively applied daily. They can make a significant difference to your immune health, improve the function of the immune system and your overall health and wellbeing.

Importantly, utilising these nutrients therapeutically is supported by many scientific studies cited below, as well as valuable feedback from other practitioners and some doctors, and my own clinical experience of 10+ years.

Let’s get started!

4 key nutrients for good immune health

ZINC

Why take zinc for immune support?

Zinc has strong antiviral properties and has been shown to directly inhibit and /or stop viral replication in cells in a short period of time. It can also help to strengthen the immune system, balance an immune response during infections, including viral respiratory infections.

The key action of zinc that is most relevant to viral infections: zinc inhibits viral and bacterial growth and replication at the cell level, and is found in high concentrations in white blood cells of the immune system. During an infection the immune system needs to produce specialised immune cells that kill viruses in the body. Zinc deficiency shows as poor resistance to infections and decreased white blood cell numbers and activity. Importantly, zinc works together with vitamin C and quercetin to further enhance the immune response to decrease the viral load.

Adequate levels of stomach acid are important for good zinc absorption from both foods and supplements. Therefore, people who experience reflux or indigestion (these are linked with lower levels of stomach acid) and other digestive symptoms, may have lower levels of zinc as seen in blood tests.

Important: there is no storage place for zinc in the body, therefore regular dietary intake and/or supplementation are necessary for many people, as deficiency may develop quickly if intakes fall.

Top food sources of zinc

Zinc is high in protein rich foods, both animal and plant. It’s best to combine the two sources in daily nutrition to optimise intake and levels. In my experience, most vegetarians and vegans need to supplement zinc to achieve and maintain levels required for good immune function.

  • Animal sources: oysters (6 to 12 oysters per week is sufficient), red meat (2-3 times per week), liver (2-3 times per month), eggs (3-6 per week), organic dairy products (if tolerant)
  • Plant sources: pumpkin seeds, sesame seeds (ground), nuts (cashews, pecans, Brazil nuts), hemp seeds, lentils, beans, buckwheat, oats, ginger root
  • Fruits and vegetables aren’t good sources of zinc but there is some in peas (especially chickpeas), cabbage and beetroot
  • Most foods high in zinc also contain vitamin D so, eating them will help to get good amounts of both nutrients

Intake and supplementation

General intake suggestions from all sources:

  • Eat foods rich in zinc daily. Combine animal and plant sources for best results
  • Supplementation: 25-30mg of zinc per day as a minimum taken with food
  • Always seek advice of a nutritionist or a naturopath before supplementing with higher amounts of supplemental nutrients, or get in touch with me for assistance.

Testing zinc levels prior to supplementation is highly recommended (see more on it below). Check your zinc levels by doing a blood test and then consider supplementing according to your body’s needs. Some people have a greater need for zinc supplementation due to certain conditions and problems with zinc absorption, often due to low stomach acid levels or pancreatic insufficiency.

VITAMIN D

Why take vitamin D for immune support? 

Vitamin D plays a very important role in enabling an effective immune response. It’s particularly needed for the activation of immune defences, including T cells and macrophages involved in combating viruses. It’s now known from studies that vitamin D prevents and/or lowers a risk of respiratory infections, both viral and bacterial. Moreover, low levels of vitamin D have been implicated in decreased lung function, which may affect the body’s ability to fight respiratory infections. 

For a quick general assessment of your current vitamin D levels, please take this short self-assessment.

Vitamin D 101

Vitamin D is primarily synthesised from UVB radiation (sunlight) by the skin where a precursor, provitamin D, is formed from cholesterol and then is absorbed to the blood through the skin. It needs to be ‘activated’ in the body, first in the liver and then in the kidneys before it can be utilised. This activation process takes around 36 hours. Having liver damage/impaired function or kidney disease can greatly decrease a person’s ability to activate vitamin D, leading to deficiency.

Importantly, vitamin D from foods or supplements also comes in an inactive form and goes through the same activation process in the body. It’s absorbed from the intestines only in the presence of dietary fats. Therefore, it’s recommended to take vitamin D supplements with meals containing good fats such as olive oil, organic butter, avocados or coconut oil.

In summary, the main reasons for vitamin deficiency are related to:

  • Not enough sunlight on the skin
  • Not enough intake from foods, low fat diets, low magnesium status
  • Liver disease
  • Kidney disease
Therefore, if you’re getting plenty of safe sun exposure, are taking vitamin D supplements and eating foods containing it, but not seeing desired increases in vitamin D levels on blood tests, you may need to assess all four factors mentioned above. Particularly, if you have liver or kidney inflammation or disease, your ability to absorb vitamin D from any source is likely compromised.

Top sources of vitamin D

  • Sunshine! It’s the best, non-toxic, cheapest and readily available source
  • Dietary sources: it’s mainly present in animal foods including cod liver oil, oily fish (sardines, herring, mackerel, salmon and tuna – fish twice per week is sufficient), liver (2-3 times per month), eggs (2-6 per week), organic butter and organic milk (from cows that actually eat grass!). Also parsley and mushrooms are good plant sources, especially shiitake and maitake mushrooms cooked in vegetable soup
  • Most vitamin D containing foods are also high in zinc so, eating them will help to get good amounts of both nutrients

Intake and supplementation

General intake suggestions from all sources:

  • Sunshine: daily sun exposure on bare skin (no sunscreen) for 20-30 minutes (middle of the day is best, between 11am to 1pm apart from summertime). Wear a hat if needed but expose hands and legs. Needless to say, it’s important to make sure that you avoid getting burnt. A few shorter periods of sun exposure are better than one longer one. Expose your face, hands and arms for about half the time it would take to get sunburned, or between 6 and 20 minutes, depending on your skin colour/tone, the season, and the distance from the Equator. Sunbathing is one of the best ways to strengthenyour immune system.
  • Supplements: generally supplemental doses can be significantly higher than the dose of 400-1000 IU per day recommended by most medical sources, depending of course on your current vitamin D blood levels. Therefore, testing is crucial and will provide necessary guidance to how much vitamin D is needed to supplement for your circumstances
  • Always seek advice of a nutritionist or a naturopath regarding a safe supplemental intake for you, or get in touch with me for assistance

I highly recommend you read my comprehensive article on what you need to know to achieve and maintain high levels of vitamin D. Information included there should answer most of your questions on supplementing with vitamin D as well as getting it from sunshine and food.

VITAMIN C

Why take vitamin C for immune support?

Vitamin C maintains normal immune system function and requirements for it sharply increase when the immune system is under stress. Therefore, infections can lead to a rapid decrease in the concentration of vitamin C in white blood cells of the immune system, also the production of antiviral immune cells slows down. 

Importantly, vitamin C is also protective of the lungs. Studies have shown that supplementation leads to improvements in the symptoms of respiratory infections. 

As vitamin C cannot be stored or made by the body it must be replaced daily through adequate intake.

Top food sources of vitamin C

  • More than 80% of vitamin C in the diet comes from fruits and vegetables. However, the amount of vitamin C in foods may be greatly reduced due to destruction during cooking, processing and storage. Vitamin C is also lost to cooking water, ageing and bruising of foods, over-cooking, reheating and slicing. Therefore, levels are usually higher in raw fruits and vegetables.
  • Best dietary sources include all citrus fruit, green vegetables (broccoli, Brussels sprouts, cabbage), leafy greens (spinach, silver beat, kale, lettuce), capsicum, chili, tomatoes, berries, fruits (strawberries, kiwi fruit, papaya), parsley, and potatoes (an important source of vitamin C! – check out this study on potatoes and vitamin C. 
  • Generally, 2-3 fruits per day plus 3-6 cups of mixed vegetables (measured raw) would be adequate for most people. 

Intake and supplementation

QUERCETIN

Why take quercetin for immune support?

Quercetin enhances the immune supporting actions of zinc in vitamin C, and it has strong antiviral properties itself.

In short, quercetin is a potent bioflavonoid compound found in brightly coloured plants. It’s one of the most abundant antioxidants found in food and also has strong anti-viral properties. Importantly, it’s a potent antioxidant and immune system modulator, helping various immune cells to work well. Quercetin’s immune supporting properties are enhanced by its mutually beneficial relationship with vitamin C.

Quercetin is also a very good natural synergistic nutrient for zinc to work effectively in the body to boost immune system function. For zinc to kill the viruses, it has to be ‘pushed’ into the cells i.e. transported across the cell membrane to the centre of the cell where viruses reproduce. When zinc is present there it can stop the virus from replicating and thus stopping an infection in its tracks in a short period of time.

Top food sources of quercetin

Daily estimated intake of quercetin from foods ranges from 50-800 mg, depending on the consumption of fruits and vegetables and the intake of tea.

  • Dietary sources: capers (most concentrated source, have 1 teaspoon a few times per week), yellow and red onions (red onions are the highest vegetable source, fried onions have more quercetin than fresh ones! – check out the study link below), red apples, berries, cherries, tomatoes, cabbage family vegetables (broccoli, Brussels sprouts, red cabbage), nuts (almonds and pistachios), red grapes, green and black tea, and red wine

Check out this study on absorption and antioxidant effects of quercetin from fried red onions!

Intake and supplementation

There’s no agreed recommended daily intake of quercetin, but most supplemental recommendations suggest between 200 and 1,000 mg daily, depending on your food intake and health status. Most studies on quercetin benefits also suggest the above-mentioned amounts.

  • Best way of getting quercetin is from foods. If you eat 4-5 servings of rainbow-coloured fruits and vegetables, it’s likely that you’re getting around 200 to 500+ mg of quercetin daily. 
  • Supplementation: if taking a quercetin supplement, seek advice from a nutritionist or a naturopath on the safe supplemental intake for you, or get in touch with me for assistance.

PROBIOTICS AND PREBIOTICS

Why take probiotics and prebiotics for immune support?

Very few people nowadays need convincing about the need to have enough of the good gut bugs to defend them against any viral and bacterial intruders. With around 70%-80% of our immune system residing in the gut lining and around the gut, it’s clear that we need to take special care of the gut and the microbiome.

As the immune system protects the body against illness, the presence of bacteria in and on the human body helps us to have a stronger and more resilient immune system. Good bacteria also strengthen your immune system and makes it more resilient.

Top food sources of probiotics

  • Food-based probiotics – fermented foods are particularly rich sources of good bacteria for a healthy microbiome. It’s easy to make them at home just like our ancestors did in the not too distant past. I have fantastic fermented food recipes on the Naturimedica website for you to start making your own – check them out here. 
  • Ready-made fermented foods such as kefir and yoghurt are very good sources of probiotic bacteria. However, many of them are either high in sugar or have chemical additives. Some even don’t have enough probiotic bacteria to make a difference. My top choice for a food-based probiotic is Tummify, developed and produced locally in Australia.
  • Tummify is made from organic milk kefir and has high/therapeutic amounts of scientifically validated good bacteria strains important for good gut health and your overall health. It also contains prebiotics i.e. food for the good bacteria, so the good bugs can feast on them and thrive. Currently, Tummify has three products on the market: Original Tummify, tummifyKids and plant-based version suitable for vegetarians and vegans. Tummify is currently available at Harris Farm, some Woolworths supermarkets and via some online delivery companies in News South Wales, soon to be expanding to other states.

Intake and supplementation

In my clinical experience, a combination of both food-based probiotics and probiotic supplementation can be an effective option for most people. Today’s diets are often overloaded with processed and take-away foods, plus high stress levels and sleep disturbances, that negatively impact the microbiome.

  • Daily intake of fermented foods and prebiotics (i.e. high fibre foods) – small amounts of fermented foods with each meal will help with overall digestion e.g. 1 tablespoon of sauerkraut 3xday with each main meal plus 1-2 shots of food-based probiotics like Tummify would be beneficial.
  • Probiotic supplements – I find that nowadays most people supplement with probiotics before they come to see me for help. As there are many benefits of probiotic supplementation confirmed by numerous studies, supplementing with probiotics has overall health enhancing effects for most.
As the knowledge of therapeutic uses of probiotics grows, we now know that consuming particular probiotic strains for specific illnesses or to correct microbiome imbalances, can significantly increase health benefits of probiotics.

Feel free to get in touch if you’d like to ensure that the probiotic you take is the right one for your health complaints or needs.

Importance of testing before supplementation

Before starting any supplementation discussed in this post, I recommend the following steps:

  1. You’ll need to know your blood levels of vitamin D and zinc to estimate how much to supplement for your needs. If your levels are low/ outside of the ones mentioned below, it’s recommended to seek advice from a naturopath or nutritionist on how much to supplement. The Zelenko Protocol below is one of the general guide to consider.
  2. Do a blood test to check your vitamin D level either through the GP or privately. Optimal levels of vitamin D are from 100+ nmol/L (40 ng/ml), and levels between 120-150 nmol/L (50-60 ng/ml) are generally considered as sufficient and health promoting by most naturopaths and nutritionists
  3. Do a blood test to check your zinc levels (serum zinc) either through the GP or privately. Optimal levels of zinc are 14+ umol/L, and levels between 15-17 umol/L are generally considered adequate for good immune function by most naturopaths and nutritionists

As a clinical nutritionist and naturopath, I require at least one consultation before recommending and/or prescribing any supplements or making dietary recommendations. This is to ensure all factors and circumstances are taken into account, and have sufficient information to provide personalised and safe recommendations. If you’d like help with testing and results interpretation, you can get in touch with me here.

For general supplementation guidelines relating to zinc, vitamin D, vitamin C and quercetin, please review the Zelenko Protocol available here. 

Read about Dr Vladimir Zelenko and his extensive experience here.

Supplement sourcing and further support

Most supplements mentioned above are available at the chemists or health food shops. If you need further assistance with selecting suitable supplements for you, please consider joining my online dispensary called Vitaly. Once ordered, the supplements will be delivered directly to your home. You can register HERE.

Once you’ve had registered, I’ll be able to recommend and prescribe suitable supplements, providing we’ve had at least one online consultation to ascertain your current health status and needs.

At present, I’m contacted daily for personalised advice on how to strengthen the immune system with nutrition and supplements. If you’d like help with navigating the supplement maze out there, consider making an online appointment with me to review your current supplements, self-prescribed or otherwise.

I especially recommend getting in touch for people who are taking multiple drugs together with self-prescribed herbs and/or supplements. There may be concerning interactions/ consequences when taking the drugs and supplemental nutrients at the same time that need to be considered and carefully checked.

You can book a Zoom or phone consultation with me here.

Bottom line

Your immune system works tirelessly everyday 24/7. It relies on your self-care, daily good nutrition and beneficial lifestyle choices to protect and serve you well. Consuming and supplementing the 4 beneficial nutrients will strengthen your immune system on a daily basis and also improve your overall health.

Arguably, applying food as medicine is the oldest, safe and effective method ever discovered and is still used with considerable success today! Let’s reap the many benefits of following this health-giving pathway given to us by Nature.

I sincerely hope the data and information provided in this post will help you to better understand how your immune system works, what it needs to function well and what you can do about it.

If you’d like help with strengthening your immune system using food as medicine and with supplements, feel free to contact me to arrange a free 25-minute initial discussion or book an online consultation HERE.

Please leave your thoughts and feedback by adding a comment below – but remember, I can’t offer personal medical advice online, so be sure to focus on sharing your health journey, valuable tips and what you’ve experienced and learnt so far. Thank you!

Good health and blessings

Joanna - signature-segoe-line

Joanna Sochan
Wholistic Health and Lifestyle Therapist
Natural and Lifestyle Therapies for Abundant Health and Wellbeing

Disclaimer: The above material is for informational and educational purposes only. It should not be used to self-diagnose and it is not a substitute for a medical advice, diagnosis, treatment, prescription or recommendation. All viewers of this content, especially those taking prescription or over-the-counter medications, should not make any changes in their health regimen or diet before first consulting a doctor or other qualified health provider with any questions they may have regarding a medical condition or their particular circumstances.

Joanna Sochan is a Natural Therapist and founder of Naturimedica Holistic Wellcare. She has a passion for helping clients transform their lives by becoming healthy and well naturally. Joanna has 12+ years experience in clinical practice and has special interest in solving complex cases, gut health, food sensitivities, hormone imbalances, autoimmune disorders and weight loss. She helps clients individually (mostly online) Australia-wide and also offers online therapeutic programs, eCourses and self-help eBooks. View full bio.

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