Fuel your immune system this winter

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  • Currently, the state of our immunity is more important than ever.  
  • The role of nutrition in maintaining and supporting our immune system cannot be ignored.
  • By eating a balanced diet rich in whole, nutrient-dense foods, we can remain healthy this winter.

During the Covid-19 pandemic, the importance of our immune system has been a topic of great interest.

It is a well-known fact that a well-functioning immune system is essential to fight off infectious micro-organisms and keep the common cold and flu at bay – and that it can also support us in our fight against Covid-19. But how do we protect ourselves from the herd of pathogens that are constantly evolving to get better at infecting us? 

You might have heard that special foods or vitamins can boost your immune system and that a healthy diet is the key to battle colds and flu. This is true. It is hard to ignore the role of nutrition in maintaining and supporting our immune system. But to find the link between food and immunity, we first need to understand the immune system.

What is the immune system?

The immune system is the mechanism your body uses to protect you from invaders such as viruses, bacteria and diseases. Your immune system is made up of two parts, innate (natural) and acquired (learned) immunity.

It is the bodyguard that protects you against pathogens, recognises invading micro-organisms and attacks and eliminates the threat. Our job is to provide this bodyguard with the ammunition to support optimal protection against infections.

Numerous studies have done research on the effects of nutrition on the immune system. The research has indicated several micronutrients whose availability is vital for optimal immune functioning. These include vitamin A; vitamins B6, B9 and B12; vitamin C, E and D; and minerals such as selenium, zinc, iron; and fibre.

These vitamins and minerals are essential micronutrients, meaning the body cannot make its own in sufficient quantities. We need these micronutrients to perform bodily functions and can only obtain them through our diet or supplements. If we do not ingest enough of them, we can develop a micronutrient deficiency that impairs our immunity.

Now that we know what vitamins we require, we need to find out where we can get them.

Vitamin D

Vitamin D helps to regulate both the innate and acquired immune system. It facilitates the maturation, differentiation, and responsiveness of immune cells.

  • Sources include sunlight (a few minutes with bare skin in the sun per week), cod-liver oil, fatty fish like mackerel, salmon and sardines, egg yolks and fortified foods such as fortified cereals or plant milks.
  • The recommended daily allowance (RDA) for vitamin D is 15 mcg/day for ages 1 to 70, male and female. Approximately 80 g of mackerel provides 20 mcg of vitamin D.

Vitamin A

Vitamin A is an example of an antioxidant that protects the body cells form breaking down. It’s essential for maintaining the mucus membranes and immune cells lining the airways and digestive tract that protect the body against outside invaders such as colds and flu.

  • Sources include chicken liver, eggs, milk, yellow, orange and dark green fruits and vegetables, such as carrots, butternut and spinach.
  • The RDA for vitamin A is 700 and 900 mcg/day for females and males, respectively. This can be obtained by eating two medium carrots per day.

Vitamin C

Vitamin C is another important antioxidant that directly influences the immune system and supports better immune function.

  • Sources include citrus fruits such as lemons, oranges and tangerines (naartjies). Other sources are bell peppers, tomatoes, and leafy green vegetables such as broccoli.
  • The RDA for vitamin C is 75 and 90 mg/day for females and males, respectively. Eating one large orange provides about 98 mg of vitamin C.

Selenium

Selenium is found in almost every cell in the body but is most abundant in the tissues of the immune system. Selenium is also an antioxidant that protects the body’s cells form breaking down.

  • Sources include Brazil nuts, red meat, seafood and plant sources such as oats and rice.
  • The RDA for the average adult is 55 u/g per day. Research shows that a single Brazil nut contains more than your RDA. The amount of selenium in food sources varies because it’s greatly influenced by the amount of selenium available in the soil. Eating a variety of selenium-containing foods is therefore a better option.

Zinc

Zinc ensures that the cell membranes of the body are kept intact to prevent invaders from entering the body. It also provides antimicrobial properties that reduce the viral load in the body and help it to heal faster.

  • Sources include oysters, red meat, beans, whole grains and fortified cereals.
  • The RDA of zinc is eight and 11 mg/day for females and males, respectively. Zinc in animal sources has a higher bioavailability compared to plant-based sources. About 100g of beef can help you achieve your RDA. Alternatively, two cups of beans also roughly contain 8 mg. But your intake doesn’t need to come from a single source. For example, two slices bread made with fortified flour contain about 2 mg of zinc, so a variety of plant-based sources can help you reach your target.

Iron

Iron plays an important role in the multiplication and maturation of immune cells and supports the acquired immune system to protect the body.

  • Sources are red meat, beans, nuts, seeds, fortified grains and cereals and dark green leafy vegetables.
  • At least 8 mg of iron is needed to reach your RDA, and as with zinc, animal sources are more easily absorbed by the body than plant-based sources. You can obtain that with about 1½ cups of cooked lentils or beans, or a variety of animal-based product such as 100–150 g of beef plus an egg. However, aiming for a variety of foods that contain iron is more realistic, especially since eating too much red meat is not considered healthy. Consuming vitamin C-rich foods along with iron-containing foods boosts absorption.

Fibre

It is, however, not only our diet that affects our immunity, as various other factors like age, stress, sleep, and overall health are also important. The gut microbiome is also closely linked to your immunity, and fibre play an important role:

Immune cells in the gut interact with a wide variety of microorganisms and are directly affected by our diet and lifestyle. The foods we eat influence the diversity of our gut bacteria, which, in turn, affects immune cells. Your gut bacteria and immune cells are at their healthiest and support strong immunity best when you consume a variety of plant foods high in fibre. A fibre-rich diet provides the gut microbiota with an energy source, and reduces the inflammatory response (which can cause havoc when excessive), which, in turn, supports optimal immune function

To summarise

All foods contain different micronutrients, and that’s why it is important to build a diet full of variety and balance if we want to support our immune system. There is no one magic-bullet nutrient or food, and supplementation will only get you so far if other dietary items (and your lifestyle) compromise your health.

The immune system might be one of the most complicated and interconnected systems in the human body. It works tirelessly to protect us from invading pathogens that threaten our health. You can support your immune system this winter by eating a balanced diet and maintaining a healthy lifestyle. 

Nicolene Kruger and Mikyle Rodrigues are final year BSc Dietetics students at the University of Stellenbosch.

The information in this article is for entertainment and educational purposes only and cannot replace a consultation with a dietitian or doctor. Visit www.adsa.org.zato find a dietitian in your area.

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