Your immune system is your body's natural defence network. Rather than being a single organ, it is a highly coordinated system involving specialised cells, tissues, organs and chemical messengers that work together to recognise and respond to potential threats.

The body's first line of defence begins with physical barriers such as the skin and the mucous membranes of the respiratory and digestive tracts. Behind these barriers is the innate immune system, which responds quickly when something unfamiliar is detected. The adaptive immune system provides a more specialised response and can develop immunological memory, allowing the body to recognise certain pathogens it has encountered before.

Food First: Where Immune Nutrients Come From

Your immune system is active every day, whether you are aware of it or not. Immune cells are continually being produced and renewed, protective barriers need to be maintained, and an intricate network of cells and chemical messengers is constantly communicating throughout the body.

All of this requires energy and nutrients.

There is no single food that can “boost” the immune system. Instead, normal immune function depends on adequate nutrition as a whole. Protein and essential fatty acids matter, as do a surprisingly large number of vitamins and minerals.

Among the nutrients with established roles in normal immune function are vitamins A, B6, B12, C and D, folate, iron, copper, selenium and zinc.

A varied diet is therefore a sensible place to start.

Zinc is found in foods such as shellfish, meat, seeds, nuts, legumes and whole grains.

Selenium occurs in Brazil nuts, fish, seafood, eggs, meat and grains. An interesting detail about selenium is that the amount found in plant foods can vary considerably according to the soil in which they were grown.

Vitamin C is found in many fruits and vegetables, including citrus fruits, kiwi, berries, peppers, broccoli and other cruciferous vegetables.

Vitamin A is present in animal foods, while carrots, sweet potatoes, leafy greens and other colourful vegetables provide carotenoids, some of which the body can convert into vitamin A.

B vitamins and folate are distributed across many different foods, including leafy vegetables, legumes, whole grains, eggs, dairy products, meat and fish. Vitamin B12 occurs naturally mainly in foods of animal origin.

Iron comes from both animal and plant foods. Meat and seafood provide haem iron, while legumes, seeds, whole grains and leafy vegetables provide non-haem iron.

Copper is found in foods including nuts, seeds, shellfish, whole grains and cocoa.

This is one reason variety matters. A handful of seeds provides something different from a bowl of berries, leafy vegetables provide something different from eggs, and mushrooms have a very different nutritional and chemical profile from citrus fruit.

The aim is not to find the perfect “immune food”, but to give the body a broad nutritional foundation from which the immune system can do its normal work.

It is also worth distinguishing correcting a deficiency from simply taking more. If someone is deficient in an essential nutrient, restoring an adequate intake matters. But once requirements are met, taking increasingly large amounts does not necessarily create an increasingly effective immune system. More is not always better.

Antioxidants and Oxidative Stress

The word “antioxidant” appears everywhere in the wellness world, but what does it actually mean?

Our cells continuously produce reactive molecules, including reactive oxygen species (ROS), as part of normal metabolism. Immune cells also deliberately produce some of these molecules as part of immune signalling and defence.

So free radicals and reactive oxygen species are not simply “bad”.

Problems can arise when the production of reactive molecules exceeds the body's ability to regulate them. This imbalance is known as oxidative stress. Excessive oxidative stress can damage lipids, proteins and DNA.

The body therefore has its own sophisticated antioxidant defence systems. These include enzymes such as superoxide dismutase, catalase and glutathione peroxidase, together with compounds such as glutathione.

Nutrition is part of this system too.

Vitamins and minerals participate in antioxidant protection in different ways, while plants provide a vast range of naturally occurring compounds including polyphenols and carotenoids.

This is where eating a colourful and varied diet becomes interesting. Berries, herbs, spices, cocoa, vegetables, fruit and tea do not all provide the same compounds.

Green tea, for example, contains a characteristic group of polyphenols known as catechins. Matcha is made from finely ground green tea leaves, so rather than drinking only an infusion of the leaf, the whole powdered leaf is consumed.

The important idea is balance. Reactive oxygen species themselves participate in normal immune signalling and defence. The goal is not to eliminate them, but for the body's oxidant and antioxidant systems to remain appropriately regulated.

Hydration Matters Too

Water rarely gets mentioned alongside vitamins, minerals and botanicals, but adequate hydration is fundamental to normal physiology.

It is particularly interesting when we look at the body's first lines of defence.

The surfaces of the nose, throat and respiratory tract are lined with specialised mucous membranes. In the airways, mucus helps trap inhaled particles and microorganisms. Beneath it, microscopic hair-like structures called cilia beat rhythmically, helping move mucus and trapped material along the respiratory tract.

This process is known as mucociliary clearance, and it is an important part of the respiratory system's innate defence.

For this system to work normally, the airway surface needs the right fluid environment. Mucus is largely water, and its hydration influences how effectively it can be transported by the cilia.

This gives us a rather different way of thinking about hydration. Drinking water is not an “immune booster”, but water is part of the basic physiological environment in which the body's protective barriers operate.

The nose and throat are therefore not simply places where we notice discomfort when something goes wrong. They are part of the interface between the body and the outside world.

Movement and the Immune System

Exercise and immunity have a more interesting relationship than the familiar phrase “exercise boosts your immune system” suggests.

When you exercise, immune cells respond.

Physical activity changes circulation, hormones and signalling molecules, and different populations of immune cells temporarily move between the blood and tissues. These changes are part of the body's normal response to physical activity.

Over time, regular moderate physical activity is associated with beneficial effects on immune regulation and overall health.

But intensity matters.

A walk, a cycle ride or a regular strength-training session does not place the same demands on the body as hours of strenuous endurance exercise. Very long or demanding exercise sessions create a much larger physiological stress response and can produce different short-term changes in immune activity.

This is another reason why thinking in terms of “boosting” immunity is misleading.

The immune system is dynamic. It responds to what we eat, how we move, whether we are resting or active, and what demands the body is facing at that particular moment.

Regular movement is part of that bigger picture.

Sleep, Stress and the Immune System

The immune system does not switch off when you go to sleep. In fact, immune activity follows distinct daily rhythms.

Sleep, the immune system and the body's circadian clock are closely connected. Different immune cells and signalling molecules change their activity across the 24-hour cycle, and sleep provides a different physiological environment from wakefulness.

Communication also works in both directions. The nervous system, endocrine system and immune system continually exchange signals.

This becomes particularly interesting when we look at stress.

A short-lived stress response and long-term psychological stress are not the same biological situation. Acute stress can temporarily redistribute immune cells and alter immune activity as the body prepares to respond to an immediate challenge.

Chronic stress is different. Persistent activation of stress-response systems, including signalling through the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis, can alter immune regulation over time.

Sleep adds another layer. Research increasingly shows that disrupted or insufficient sleep is associated with changes in immune and inflammatory processes.

So supporting normal immune function is not simply a question of finding the right vitamin, herb or mushroom.

Food, sleep, movement, hydration, stress, the body's physical barriers and the immune system itself are interconnected.

That is why we prefer to think about immune health as a system rather than something that needs to be continually “boosted”.