The eight nutrients you need for optimal immune function (and the foods and meals that actually contain them)

With Coronavirus (COVID-19) looming large, we are certainly living in interesting times!  

With no vaccine on the horizon for many months or years, it’s more important than ever to prioritise foods that contain the nutrients that your immune system needs to fight off COVID-19 when you are exposed. 

Data from China indicates that those who are older or who have pre-existing metabolic health-related conditions such as cardiovascular disease, diabetes, respiratory issues or hypertension have a significantly higher chance of more severe symptoms, including death.  

Elevated blood sugars tend to correlate with immune system dysfunction.  This video explains the mechanism for the medically inclined.

People with more body fat also tend to have a higher respiratory quotient (RQ) and tend to rely on their glucose burning (aerobic) metabolism and hence are more susceptible to being out of breath (note: hypoxia is a key symptom and cause of death COVID-19).

Due to oxidative priority, your body has to burn off any excess glucose in your system before fat and we consume around 30% more oxygen when be burn carbohydrates compared to fat.

While it can be argued that people in China may not have the same nutritional status (e.g. lower selenium in many areas) and perhaps less access to health care compared to people in more affluent western countries, it is also possible that more affluent countries have a higher risk due to higher rates of obesity and poor metabolic health.  

Optimising Nutrition advisor Dr Brian Lawenda has created this handy tool to calculate your risk of death if you are infected with COVID-19 based on the current preliminary data coming out of China.

While good hygiene is the first line of defence, along with good sleep, exercise and stress management, the final line of defence is your immune system.  Having adequate nutrients that support your natural immune function and increase your ability to carry more oxygen in your blood will be critical to reducing the severity of the symptoms of Coronavirus when you are exposed.

But rather than living in fear and waiting for the worst, what can you do to give your immune system the best chance?  

Malnutrition and immunity 

Our intake of the essential micronutrients (i.e. vitamins, minerals, essential fatty acids and amino acids) plays a central role in your body mounting a healthy immune response.  Poor nutrition can lead to deficiencies in certain micronutrients that are required for immune function.

Chronic malnutrition is a significant risk factor for global morbidity and mortality.  More than 800 million people are worldwide are estimated to be undernourished.  While this is more prevalent in developing countries, undernutrition is also a problem in industrialised nations, especially in the elderly and obese.  

What is a healthy well-balanced diet anyway?

Opinions are divided about what you should do nutritionally to boost your immune system.  

There is no end of herbs, pills or supplements being recommended to battle Coronavirus.  On the other end of the spectrum, you have the conservative dieticians telling you to eat a “healthy well-balanced diet”.  

Unfortunately, the question of “what is a well-balanced diet” has never really been answered clearly.  While there is endless debate about the best diet, the question of what actually constitutes optimal nutrition is becoming more critical in the face of a global pandemic where a healthy immune system is your only defence.   

While it’s always ideal to have a nutrient-dense diet that provides enough of all the essential nutrients from the food you eat, a few of the essential nutrients appear to play a special role in supporting healthy immune function (e.g. vitamin C, vitamin D, iron, selenium, zinc and omega 3). 

In the remainder of this article we will cover:   

  • why these essential micronutrients are particularly important to support your immune function, and 
  • what you should be eating to ensure you get enough of these essential nutrients in the form, quantities and ratios that your body can use.  

Should you take a supplement? 

Unfortunately, when most people think of nutrients the first thing that comes to mind is pills, like this…

… rather than nutrient-dense whole foods, like this.

A number of friends have contacted me asking for my thoughts on what supplements they should be taking to give them the best chance of fighting off COVID-19.  This can certainly be a vexing and confusing topic.

I have seen a range of options recommend online, including (in alphabetical order):

  • A “multiple vitamin” 
  • A chiropractic treatment 
  • A nap
  • Acetylcysteine (NAC)
  • Antiviral herbs
  • Anything that boosts your immune system
  • Apple cider vinegar 
  • B12
  • Baking soda 
  • Broccoli sprouts  
  • Cayenne pepper 
  • CBD
  • Celery juice 
  • Cod liver oil
  • Echinacea
  • Elderberry
  • Essential oils
  • Eucalyptus oil
  • Fasting 
  • Garlic 
  • Glutathione 
  • Green juice 
  • Green tea
  • High dose vitamin A
  • High dose vitamin C
  • High dose vitamin D 
  • Iodine 
  • Irish tea moss
  • Liquorice
  • Magnesium
  • Manuka honey
  • Nebulised silver 
  • Olive leaf extract
  • Rum 
  • Salt lamp
  • Selenium 
  • Snake juice 
  • THC 
  • Vicks
  • Zinc

So, which one of these supplements should you be taking?

All of them?

None of them?

How do you know?

How can you be sure?

Your body is a highly complex system, with many moving parts.  Regardless of what the $125 billion per year supplement industry would like you to believe, you simply can’t rely on mega-doses of supplements in pills and powders to manage your risk against a background of a nutrient-poor diet of highly processed foods.  

While the official Dietary Reference Intakes for vitamins and minerals are intended to be the minimum amount required to prevent diseases of deficiency in most people, the Optimal Intake Levels are typically 2 – 5 times higher than these minimum recommended amounts.  

But simply taking megadoses of isolated vitamins or minerals may do nothing more than put extra load on your kidneys to excrete them, particularly when they come in a supplemental form that your body does not know what to do with.  

Megadoses of supplemental vitamin C or minerals can leave you on the toilet with diarrhea.  Not only will you be excreting the excessive supplemental nutrients, but you will also end up dumping your food before your body has a chance to absorb the nutrients from it.

While gut tolerance varies from person to person, there are limits to the quantities of supplements your body can tolerate.  People with the poorest health often also typically have digestive issues and hence less chance of absorbing supplemental nutrients that come in intense doses.  

Synthetic isolated nutrients can be as powerful as drugs, and it is possible to overdose.  Excessive supplementation can easily throw your system out of balance and make things worse rather than better.  By contrast, nutrients in nutrient-dense minimally processed food work together in synergy and contain the various cofactors required for the nutrients to work together in your body.

While you can fit a lot of vitamins into a pill, minerals and amino acids are bulkier and hard to get sufficient amounts in supplemental form (at least without resorting to large quantities of powders that may cause gastric distress).

The bottom line is that getting your micronutrients from fresh and minimally processed food grown in microbe-rich soil within a thriving ecosystem will give you the best chance of getting the right amount in the ratios in a form that your body can use.  Before you spend time and money on supplements you should invest in ensuring that you are packing the maximum the nutrients you are getting from the food you eat using some of the foods detailed below.

In the following sections, we’ll look at:

  • how a number of nutrients support your immunity,
  • the research to support the efficacy,
  • which foods contain more of them, and
  • the pros and cons of getting them from supplements vs food.

If you’re short on time and just want to know what to eat to get more of these, scroll down to the Optimal Foods to Support Your Immunity section and recipes at the end of this article.

Protein 

According to the World Health Organisation, more than one-third of the world’s underprivileged are affected by Protein Energy Malnutrition which can compromise the integrity of mucosal barriers, thus increasing your vulnerability to infections of the respiratory, gastrointestinal, and urinary tracts.  

Protein Energy Malnutrition increases your susceptibility to infection by adversely affecting your immunity and adaptive immunity.  

Protein-energy malnutrition usually occurs together with deficiencies in essential micronutrients (especially vitamin A, vitamin B6, folate, vitamin E, zinc, iron, copper, and selenium).  Our analysis has consistently demonstrated that foods and meals that contain more vitamins, minerals and essential fatty acids have a higher percentage of protein.  

The chart below shows our most recent analysis of the relationship between percentage protein and the Optimal Nutrient Intake Score for our series of eighteen nutrient-dense recipe books tailored to suit a range of goals and preferences.  

The highest nutrient density on a calorie for calorie basis tends to align with around 50% protein.  However, while amino acids (i.e. protein) are essential, if you are consuming a diet that contains optimal amounts of the essential vitamins, minerals and fatty acids it’s unlikely that you will need to worry about getting more protein.  Simply eating more protein tends to correlate with a higher overall intake of calories and obesity.  

But, as we reduce ‘empty calories’ from refined fats and/or refined carbs (i.e. the majority of our modern diet) the percentage of protein in our diet tends to increase.  

While protein is required to build and repair your muscles and vital organs, you can think of fat and carbs and your energy source that may come packed with the essential nutrients you require to support your immune system.  You can dial these up or down to suit your activity or fat loss goals while ensuring you get adequate nutrients from your food.   

Potassium

Potassium and COVID-19

While it’s early days, I expect we will soon discover the important role that a range of nutrients play in immunity and your risk of exposure to Coronavirus.  One nutrient I haven’t seen listed as a magical way to defend yourself against Coronavirus is potassium. A February 2020 study showing that almost all (93%) of COVID-19 patients had low potassium levels (hypokalemia) and patients responded well to potassium supplementation.  

While not typically associated with immunity, low potassium levels are associated with most of the key risk factors metabolic-related risk factors for COVID-19 (i.e. diabetes, heart disease and high blood pressure).  

Benefits of potassium in your body 

Potassium is the third most abundant mineral in the human body.  Normal body function depends on tight regulation of potassium concentrations both inside and outside of cells.  Potassium helps you regulate your fluid balance, send nerve signals and regulate muscle contractions. Low potassium concentration in the blood (hypokalemia) can result in muscular paralysis or abnormal heart rhythms and can be fatal.  

Chronic hypertension damages the heart, blood vessels, and kidneys, thereby increasing the risk of cardiovascular disease (i.e. risk factors for COVID-19).  Increasing dietary potassium intake may help lower blood pressure as well as reducing your risk of stroke, kidney stones and osteoporosis.  

Potassium is possibly the most neglected nutrient in our food system and is deemed to be a ‘nutrient of public health concern’, with less than 2% of Americans meeting their recommended daily potassium intake.  

Nerve impulses are generated by sodium ions moving into cells and potassium ions moving out of cells.  Your nervous system relays messages between your brain and body that help to regulate your muscle contractions, heartbeat, reflexes and many other functions.  

Availability of potassium in the food system 

There has been a significant decrease in potassium in our food system since the widespread use of chemical fertilisers in the 1940s.  

Typically available foods contain less than 2 g of potassium per 2000 calories compared to the DRI of 4.7 g per day for men and the stretch target of 6 g per day. So, to achieve your minimum recommended intake (let alone optimal levels), you will need to go out of your way to chase more potassium in your diet.  

Satiety response to increased potassium

Our satiety analysis suggests that people who consume more potassium in their diet tend to consume around 30% fewer calories.  This satiety response is stronger for potassium than any other micronutrient. Only protein has a stronger satiety response than potassium! 

The Recommended Daily Intake (RDI) for potassium is 4.7 g per day for an adult male while the Adequate Intake is 2.3 g/day.  Potassium is the only nutrient that the average for Optimisers is less than the RDI.  

Potassium stretch targets 

Based on the powerful satiety response data, we have set a stretch target of 5.5  g of potassium for men and 4.4 g for women. Once you have started to get the hang of nutrient density, you could ‘level up’ by aiming for these stretch targets to truly optimise your nutrition.  

nutrient averageRDIAI stretch (men)stretch (women)
potassium (g)3.64.73.45.54.4

Synergistic nutrients 

Potassium works synergistically with vitamins B6, D, bicarbonate, calcium, insulin, magnesium, phosphate and sodium.   

Potassium supplements 

If you do choose to supplement, you should start slowly.  Potassium supplements in tablet or capsule form are limited to 99 mg because they can affect heart function if you are on medications.   

If you want to make sure you are getting enough potassium, we recommend you track your diet in Cronometer to check if you are meeting your targets.   

Potassium-rich food sources 

Foods highest in potassium tend to be green veggies such as the ones listed below (i.e. not bananas!):

  • parsley  
  • zucchini
  • lettuce
  • cauliflower 
  • asparagus  
  • kale  
  • cucumber
  • broccoli  
  • sauerkraut
  • green peppers
  • cabbage 
  • turmeric 
  • sweet potato  
  • kiwifruit  

Vitamin C

What does vitamin C do in your body?

Vitamin C is an essential nutrient because humans (along with guinea pigs, fruit bats and other primates and mammals) can’t make their own.  It is thought that humans lost their ability to make Vitamin C because it was plentiful in our traditional diets.

Vitamin C protects your cells against reactive oxygen species that are generated by immune cells to kill pathogens.  Vitamin C also contributes to your immune defence by supporting various cellular functions of your immune system.   

However, while it is widely thought that supplemental vitamin C boosts the function of the immune system and can ward off the common cold, a Cochrane review of controlled studies indicates that supplementation vitamin C showed only a mild benefit.  

Synergistic nutrients

Vitamin C works synergically with vitamins A, B5, B6, B12, E calcium, copper, folate, iron, lysine, magnesium, magnesium, methionine, phosphorus and zinc.  Hence, it’s ideal to get your vitamin C from foods that contain a full spectrum of micronutrients.

Foods that contain vitamin C (along with other synergistic nutrients in the form that your body knows what to do with) appear to be beneficial, but relying on supplements alone is ill-advised.  

Losses

Losses of vitamin C during processing can range from 10 to 90%.  

Vitamin C is highly unstable and degrades in response to heat, light and alkalinity.  

Hence, it’s critical to focus on getting your vitamin C from fresh and minimally processed food.   

Bioavailability 

Your absorption of Vitamin C depends on how much you’re consuming.  Your stomach regulates absorption into your body based on demand.  

At lower doses of 30 to 180 mg per day, approximately 70%–90% of vitamin C is absorbed. However, at doses above 1 g/day, absorption falls to less than 50%.  

Unmetabolized Vitamin C is excreted in the urine, but higher intakes of supplemental vitamin C tend to cause gastric distress.  

Dietary Reference Intake

The Dietary Reference Intake (DRI) for Vitamin C is 45 mg per day with an Estimated Average Requirement (EAR) of 30 mg/day.  However, concerningly, only 31% of adults in the US do not meet the EAR from their food.  

Upper Limit 

The Upper Limit (UL) for Vitamin C intake is set at 2000 mg/day due to gut tolerance.   

Stretch target from food

Our satiety analysis shows a moderate satiety response to foods that contain more vitamin C.  People who consume foods that contain more Vitamin C tend to consume around 15% fewer calories than people who consume foods that contain less vitamin C.  Practically, it is hard to obtain more than 1000 mg/day from food.  

Based on our satiety analysis, we have set a stretch target for vitamin C of 400 mg per day for women and 500 mg per day for men.  

nutrient EAR RDIstretch (men)stretch (women)
Vitamin C (mg)3045500400

Foods that contain more vitamin C

Foods the contain more vitamin C on a calorie for calorie basis include:

  • kale  
  • broccoli  
  • parsley
  • green peppers
  • cauliflower 
  • lemon juice
  • cabbage
  • kiwifruit 
  • lime juice
  • oranges
  • zucchini
  • sauerkraut
  • raspberries 
  • asparagus 
  • lettuce
  • sweet potato  
  • garlic
  • cucumber
  • onion
  • Blueberries

Vitamin D

What does vitamin D do in your body?

Vitamin D is an essential fat-soluble micronutrient that acts as a hormone in your body to support many vital functions and processes.   

Low vitamin D is considered a major public health concern, with 13% of the world’s population thought to be deficient.  Those who live further away from the equator are at more risk.   

Adequate vitamin D is critical to maintaining strong bones because it is critical to facilitate the absorption of both calcium and phosphorus.  

Vitamin D also together with vitamin A to support healthy immune system function.  

Vitamin D3 is a potent modulator of the immune system and helps protect against infections caused by pathogens.  

Losses

Ironically, given that vitamin D is synthesised by the sun, vitamin D in food and supplements is unstable and degrades in the presence of light. 

Synergistic nutrients

Vitamin D works synergistically with vitamins A, B3, K, boron, calcium, copper, magnesium, manganese, phosphorus, sodium and calcium.    

Bioavailability 

Vitamin D2 (ergocalciferol) is made by plants while D3 is the form synthesised by animals.  If you’re eating plenty of vitamin D containing foods and/or supplementing, then either form is fine.  However, if you are not supplementing regularly, ensuring your food contains plenty of vitamin D3 is ideal.   

Upper Limit 

Vitamin D toxicity (hypervitaminosis D) does not result from sun exposure.  However, hypercalcemia (i.e. excessive absorption of calcium) has been observed in people supplementing high doses of vitamin D.  Excessive absorption of calcium (e.g. in your arteries) can become a serious issue.  Hence, an Upper Limit for supplementation of vitamin D has been set at 4,000 IU per day.  

How much vitamin D do you need?

While vitamin D can be obtained in foods like fatty fish, your body synthesises it when exposed to the sun.  It is harder to get vitamin D from food alone without sun exposure.  

The Adequate Intake level of vitamin D (i.e. 10 micrograms per day for adults less than 50 years old) is based on the amount in the diet to maintain healthy blood levels of vitamin D without significant exposure to sunlight.  

Foods that contain more vitamin D

Foods with more vitamin D are listed below.  

Plant 

  • spinach 
  • blackberries  
  • kale  
  • raspberries 

Seafood 

  • mackerel
  • salmon
  • sardines

Other 

  • turmeric 
  • cinnamon 
  • tea
  • black pepper 

Vitamin A

What does vitamin A do in your body?

Vitamin A is a fat-soluble vitamin that is critical to support your vision, fertility and reproduction.  Vitamin A helps your heart, lungs, kidneys, and other organs work properly and plays a critical role in maintaining your immune system, preventing infection and reducing acne.  

Vitamin A supports both your innate and adaptive immunity as skin and mucosal cells of the eye and respiratory, gastrointestinal forms a barrier against infections.   You will be more vulnerable to infection if you are not getting enough vitamin A.

Synergistic nutrients

Vitamin A works synergistically with vitamins B2, B3, B12, C, D, E, magnesium, selenium, manganese, potassium, phosphorus, iodine, tyrosine and zinc.   

Bioavailability 

It’s important to be aware that vitamin A comes in two forms:

  • Provitamin A, and 
  • Preformed vitamin A.

We obtain provitamin A plant-based foods (e.g. carrots), while preformed vitamin A is found in animal-based products and seafood.  

Most people can convert adequate amounts of provitamin vitamin A to preformed vitamin A, but only if they are getting enough in their diet.  

Availability in the food system

Vitamin A deficiency is a significant issue, especially in developing nations where the availability of foods containing preformed vitamin A (i.e. animal-based foods) are more limited.

The chart below (with data from the USDA Economic Research Service) shows that the availability of vitamin A in our diet has decreased since the introduction of the US Dietary Guidelines in 1977.  

The amount of vitamin A typically available in the food system is now well below the Estimated Average Requirement (EAR) and the Daily Recommended Intake (DRI), hence most people need to prioritise foods that contain more vitamin A.  

Upper Limit 

The Upper Limit for vitamin A (10,000 IU) is based on abnormal liver pathology in adults and developmental issues in babies of women taking excess supplementary Preformed Vitamin A.  Vitamin A is fat-soluble, so it is harder to excrete than water-soluble vitamins.  So you should be careful when taking vitamin A supplements (which are preformed vitamin A).  

While rare, you can get excessive levels of preformed vitamin A from animal products such as liver.  Some animals (e.g. seals, polar bears, halibut and huskies) have very high levels of vitamin A in their livers.  There have been isolated reports of hypervitaminosis A when hungry and dehydrated explorers consume livers from these animals.  But otherwise, significant cases of hypervitaminosis A from food is uncommon. 

Stretch target from food

Our satiety analysis shows that foods with more vitamin A tend to be more satiating.  People consuming more vitamin A tend to eat about 10% fewer calories than those consuming less vitamin A.   

Foods that contain more vitamin A

Foods the contain more vitamin A on a calorie for calorie includes:

Plant based 

  • lettuce
  • kale  
  • parsley  
  • sweet potato  
  • almond milk
  • asparagus  
  • broccoli  

Animal 

  • lamb liver
  • beef liver
  • chicken liver
  • whole egg
  • Parmesan cheese 
  • brie
  • milk  
  • cottage cheese  

Seafood 

  • shrimp
  • salmon

Note:  Vegetables contain pro-vitamin A which your body converts to preformed vitamin A before use, while animal and seafood contain preformed vitamin A which does not need to be converted.

Iron

What does iron do in your body?

Iron is a crucial component of proteins and enzymes that are involved in oxygen transport and storage, electron transport and energy generation, antioxidant and beneficial pro-oxidant functions, and DNA synthesis. 

Iron is an essential component of hemoglobin.  Given that hypoxia is a major symptom of COVID-19 it is likely that having adequate iron in your diet will reduce your symptoms and reduce your risk of needing hospitalisation and competing for the limited supply of respirators.  

Iron is required to mount effective immune responses to invading pathogens and a deficiency in iron will impair your immune responses.  

While having an adequate dietary intake of iron is critical, studies have shown that there can be an increased risk of malaria with iron supplementation against the background of a nutrient-poor diet.  

A Cochrane review of controlled studies found no benefit in terms of respiratory tract infections from iron supplementation.  So again, you need to ensure you are doing everything you can to get the nutrients you require from the food you consume rather than putting your faith in supplements.

Heme iron vs non-heme iron

Iron in our diet comes in two forms: 

  • heme iron (from animal-based foods), and 
  • non-heme iron (from plant-based foods).  

Bioavailability 

We absorb 15 to 35% of animal-based iron while you will only absorb 2% of plant-based iron.  Hence, you may be at risk of anemia if you follow a strict vegan diet.  

However, if you are consuming a nutritious omnivorous diet you are unlikely to have significant issues with low or high iron levels unless you have digestive problems, consume a lot of grains or minimal vitamin C (all of which will affect the absorption).  

Vitamin C supplementation will increase your iron absorption.  However, this is not necessarily a good thing as high ferritin levels are associated with inflammation. 

Availability of iron in the food system

As shown in the chart below, the availability of dietary iron has increased with the introduction of iron-enriched foods, particularly breakfast cereals.  

Ironically though, iron absorption is also negatively affected by the phytates in the grains. The form of iron used in fortification is also not ideal as it may cause constipation, feed pathogenic gut flora and contribute to oxidative stress that damages the intestines.  So it is not ideal to rely on fortified cereals for your iron.

Synergistic nutrients

Excess iron intake can affect zinc absorption and vice versa.  If your dietary ratio of iron:zinc is higher than 2:1 then your absorption of zinc will be reduced.   

Dietary Reference Intake

The Estimated Average Requirement for iron of 6 mg and the Recommended Daily Intake for iron of 8 mg/day for men, with higher intakes recommended for women of reproductive age.

Upper Limit 

The Upper Limit of 45 mg/day has been set to prevent gastrointestinal issues.   

Stretch target from food

Our satiety analysis shows that people consuming food that contain more iron tend to eat around 20% fewer calories than those who consume less iron-rich foods.

Based on this analysis, we have set a stretch target of 30 mg/day for both men and women.  

nutrient averageEAR RDIULstretch (men)stretch (women)
iron (mg)186/88/18453030

Foods that contain more iron 

Foods that contain more iron are listed below.

Animal 

  • chicken liver
  • lamb liver
  • beef liver
  • whole egg
  • ground beef  

Vegetables 

  • parsley 
  • asparagus  
  • sauerkraut
  • lettuce
  • kale  
  • broccoli  
  • zucchini
  • cucumber
  • green peppers
  • cauliflower 
  • raspberries 
  • garlic
  • flax seeds
  • sweet potato  
  • cabbage
  • onion
  • kiwifruit 
  • blueberries
  • grapes
  • cashews
  • almonds
  • walnuts

Note: Iron from plant-based foods are less bioavailable.

Selenium

What does selenium do in your body?

Selenium is an essential mineral that plays a significant role as an antioxidant, helps you regulate your thyroid and helps to protect you from oxidative damage.   Selenium plays an important role in your immune system by slowing the body’s over-active responses to certain aggressive forms of cancer. 

Selenium is thought to help with the prevention of some cancers, protect against heart disease, prevent cognitive decline and relieve with asthma symptoms.  

However, the selenium content of your food depends heavily on the content of the soil that the food is grown in. Certain parts of China, where large proportions of the population have a primarily vegetarian diet and the level of selenium in the soil is very low, have the lowest selenium intake in the world and these low selenium intake areas correspond to a 69% higher risk of thyroid disease.  

The map of China below shows how the selenium content of the soil decreases as we move away from the coast (i.e. blue = low, red = high).  A 2017 paper found a close correlation between both selenium and omega 3 intakes and longevity.  Average selenium intakes are also low in some European countries, especially populations consuming predominantly vegan diets.  

In view of its role in immunity, it is possible that a higher intake of selenium in western countries may reduce the risk and severity of infection with COVID-19 compare to the low selenium areas in China

Synergistic nutrients

Selenium works synergistically with vitamins B3, C, E, cysteine, glutathione, methionine, zinc and iodine.   

Dietary Reference Intake

The Estimated Average Requirement of 0.05 mg/day and the Recommended Daily Intake of 0.07 mg/day for men.  The recommended minimum intake of selenium for pregnant women is 60 mcg/day and 70 mcg/day for breastfeeding women.   

Upper Limit 

Although selenium is required for health, high doses of selenium can be toxic and fatal, and hence the Upper Intake Level of selenium has been set at 400 ug/day.   

Stretch target from food

Our satiety analysis shows that foods with more selenium tend to provide significantly greater satiety.   People who eat foods that contain more selenium tend to eat about 25% fewer calories.  

Based on this satiety analysis, we recommend a stretch target of 300 ug/day for men and 240 ug/day for women.    

nutrient averageEAR RDIULstretch (men)stretch (women)
selenium (ug)1905055400300240

Availability of selenium in the food system 

The chart below shows the selenium content of foods generally available that will provide you with enough selenium to meet the Recommended Daily Intake for selenium of 44 ug/day.  Still, you will need to prioritise nutrient-dense foods to meet more optimal levels.  

It appears that selenium fortification of food was ramped up in the mid-1970s after a decline in selenium content in the food system after the introduction of synthetic fertilisers and industrial agricultural practices (data from USDA Economic Research Service).  

Foods that contain more selenium

Foods that contain more selenium include:

Plants 

  • asparagus  
  • broccoli  
  • garlic
  • flax seeds
  • kale  
  • sauerkraut
  • cabbage
  • cauliflower 
  • lettuce
  • cucumber
  • onion
  • zucchini

Animal 

  • liver
  • egg 
  • cheese  
  • milk 
  • ground beef  

Seafood 

  • shrimp
  • salmon

High fat foods

  • brazil nuts
  • bacon
  • cashews

Zinc

What does zinc do in your body?

Zinc is an essential nutrient that is a cofactor for hundreds of enzyme reactions in the human body and is critical for optimal function of the cells that control your immunity.  Even marginal zinc deficiency can suppress aspects of immunity

In addition to your immunity, zinc is critical to a wide range of bodily functions, including reproduction, skin health and vision.   Older people are particularly at risk for zinc deficiency due to inadequate dietary zinc intake.  Plasma zinc levels also decline with age.

Losses

Zinc in meat is not significantly depleted by cooking.  However, you will lose some zinc via the liquid when cooking vegetables.  

Synergistic nutrients

Zinc works synergistically with vitamins A, B6, D, E, cysteine, glutathione, magnesium and manganese.   Hence, it is crucial to get your zinc from nutrient-dense whole food sources that typically come packaged with these other nutrients.   

Bioavailability 

Soaking and sprouting beans, seeds and grains may improve zinc bioavailability.  

What factors interfere with zinc absorption?

Absorption of zinc is impacted by excess sugar, insufficient stomach acid, gut inflammation and allergiesExcess calcium intake impairs zinc absorption as does excess phytates (found in grains and legumes).  

Iron and zinc compete for absorption pathways, so excess iron supplementation or a high intake of foods fortified with iron can negatively impact the absorption of zinc.  

If your ratio of iron:zinc is higher than 2:1, then your absorption of zinc will be reduced.  

Absorption from animal sources of zinc is much higher than from plant sources, so strict vegans should allow an additional 50% more zinc in their diet.

However, too much zinc can interfere with your absorption of copper and vice versa.  Hence, it’s ideal to maintain your zinc:copper ratio between 10:1 and 15:1.   

Dietary Reference Intake

The Estimated Average Requirement for zinc is 12 mg/day for men and the Daily Recommended Intake of 14 mg/day.  

Upper Limit 

There is no evidence of adverse effects of high amounts of zinc in foods, and hence, there are no real symptoms of toxicity or side effects.  You will quickly excrete any excess zinc in the faeces. However, an Upper Limit of 40 mg has been set for zinc from supplements.   

Stretch target from food

Our satiety analysis indicates a strong satiety response when people consume foods and meals that contain more zinc.   

Based on our satiety analysis, we have set a stretch target of 32 mg/day for men and 25 mg/day for women.  

nutrient averageEAR RDIULstretch (men)stretch (women)
zinc (mg)206.58403225

Availability of zinc in the diet 

Zinc availability in the food system has increased since the 1930s with the widespread fortification of breakfast cereals.  As shown in the chart below, there was a significant jump in zinc fortification in the mid-1970s (data from USDA Economic Research Service). 

However, the current level of zinc in the diet still does not meet the Daily Recommended Intake or Estimated Average Requirement and is nowhere near the stretch target.  So most people will need to pay attention to zinc to ensure they get enough in their diet.   

Foods that contain more zinc 

Foods that contain more zinc tend to be shellfish, liver or non-starchy green vegetables as listed below.  Keep in mind here that animal-based sources of zinc will also be more bioavailable.

Animal 

  • ground beef  
  • Parmesan cheese 
  • milk  
  • whole egg
  • brie
  • cottage cheese  

Seafood 

  • oyster
  • crab
  • crayfish
  • squid
  • shrimp
  • anchovy

Plants 

  • parsley
  • asparagus  
  • zucchini
  • broccoli  
  • lettuce
  • cucumber
  • kale  
  • cauliflower 
  • sauerkraut

Optimal foods to support your immunity

Rather than focusing on individual nutrients, we can determine the foods that contain more of all of these nutrients that are critical to your immune system.  The list of foods below has been optimised to maximise your intake of all of the nutrients highlighted in this article that have been shown to play a key role in supporting a healthy immune response.  

Plants

  • bok choy 
  • spinach
  • nori
  • coriander/cilantro
  • parsley
  • Swiss chard
  • watercress
  • mushrooms
  • chives
  • endive
  • bell peppers
  • asparagus
  • pumpkin
  • broccoli
  • kale
  • tomato
  • Brussels sprouts
  • cauliflower 
  • broccoli sprouts
  • zucchini
  • kimchi 
  • lettuce
  • collards 
  • radish
  • sauerkraut
  • scallions
  • daikon
  • green peppers
  • snow peas
  • carrot (raw)
  • scallions (top and bulb)
  • cabbage
  • carrots 
  • celery
  • lemon
  • arugula/rocket
  • tossed salad
  • lemon juice
  • cantaloupe
  • kiwifruit 
  • alfalfa sprouts

Animal  

  • lamb liver
  • chicken liver
  • beef liver
  • sirloin steak (fat not eaten)
  • egg white
  • whole egg
  • duck eggs

Seafood 

  • oysters
  • mackerel
  • tuna 
  • cod
  • mussels 
  • salmon
  • sardines
  • caviar
  • shrimp

Other 

  • beef broth
  • turmeric 
  • oregano
  • mustard
  • paprika
  • cream of tartar
  • coconut water 
  • salsa
  • nutritional yeast
  • curry powder

Nutrient fingerprint 

The chart below shows the micronutrient fingerprint of the foods that contain more of the nutrients that will support your immune system (i.e. vitamin C, vitamin D, zinc, selenium, iron, vitamin A and potassium).   

As you can see from this chart, it’s fairly easy to obtain adequate vitamin A, vitamin C and iron while selenium and zinc are a little harder to find.  

While it’s great to get more of these nutrients that align with improved immunity, it’s even better to focus on the foods that contain the nutrients that you are not getting as much of in your diet.

Summary 

Your immune system is your body’s last defense against infections and viruses.  However, our modern heavily processed and refined diet sets us up for an increased risk of not being able to mount an effective immune response in the face of a significant challenge such as COVID-19.  

While there are many nutrients involved in supporting a healthy immune system, there are also risks and limitations if you rely on isolated supplements to get what you should obtain from your food.  

There is extensive research to show that many of the essential micronutrients play a critical role in supporting your immune system.  However, solid research demonstrating that isolated supplements alone make a significant difference is harder to come by.  

While potassium, vitamin D, vitamin C, zinc, selenium and iron all play important and complementary roles in supporting your immune system, there are many other synergic nutrients that your body requires to make the most of these key nutrients. 

It’s hard to get all of these in a pill or supplement. Excessive levels of isolated supplements can put you at risk of adversely affecting the absorption of other critical nutrients or diarrhea that will flush all the other essential nutrients from your food down the toilet.    

While supplements may play a role in supporting your immune function, they will be of limited value if you are not already doing everything you can to maximise the nutrient density of the food you eat.

Postscript: Optimised recipes

After this article was published, a couple of people asked which recipes contain more of these nutrients. So we’ve included some (free) links below the online versions of a handful of the recipes that contain more of the nutrients that will healthy immune function. We hope these will give you the best chance of maximise your natural immunity increase your resilience during this challenging time.

Marty Kendall
 

  • Anjay says:

    Broccoli in almost every list !

    • Humphrey Koraag says:

      So true! Am glad to say that I eat broccoli almost every day (with mustard added for synergistic purposes).

  • […] Maximize your intake of nutrient dense foods (great article) […]

  • Wenchypoo says:

    Just as important as what you eat is WHEN you eat…let’s not forget intermittent fasting here, as it also ramps up the immune system by old cell autophagy, creating and mobilizing new cells to repel invaders.

  • Lisa says:

    Thanks Marty great article , summary and suggestions .

  • Julianne says:

    HI Marty – just wondered if you had taken a look at anything around the cytokine storm and severity of COVID-19. I came across the effect on omega 3 levels and high dose omega 3 in ameliorating this years ago when my brother had a bone marrow transplant, and one of the main issues is graft vs host disease, which induces a severe cytokine storm. I made him take 5 grams of EPA DHA a day and he had very little GVHD. Just a thought. I haven’t looked into it much yet

    • Marty Kendall says:

      thanks heaps. I’ll have a look. all I’ve seen is risks of excessive immune response with overstimulation with excessive supplemental A, C and D. it’s still really early days in our understanding of how COVID-19. seems #foodfirst is a safe approach rather than relying primarily on supps.

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