What is Immunity, actually?

Cold and flu season is approaching, and we want to prevent - or at least, reduce - the symptoms of illness.

Our immune system is an internal surveillance system keeping us healthy and functional, but how does it actually work?

Innate vs Adaptive Immunity

The immune system has two levels of defence against pathogens:

1) Innate Immunity is our first defence against invading pathogens. It is fast and generally attacks anything that is determined to be a threat to the body.

There are 3 barrier levels to the innate immune system:

• Physical barriers (i.e. skin)

• Chemical barriers (i.e. mucous, stomach acid)

• Immune cells (white blood cells)

The innate system is always hard at work defending us against a constant barrage of bacteria and viruses, without us even noticing.

2) Adaptive Immunity is our second line of defence for anything that gets past the Innate Immune System. It is highly specialized for specific pathogens, responds rapidly, and remembers past attacks for better efficiency over time.

Within 2-3 days of an infection, the adaptive immune system ramps up, causing the tell-tale signs of illness, such as fatigue, sore throat, and possibly a low-grade fever.

Adaptive Response - Prepared for Attack

B cells and T cells are the body's way of target-locking on pathogens. B cells produce antibodies, proteins that can neutralize or tag pathogens for destruction. Specialized T cells can then identify and eliminate the targeted, infected cells.

After infection, some B and T cells remain as memory cells, which remember the pathogen so that they can respond fast to the same pathogen next time it tries to infect you. Because of this efficiency, symptoms may be noticeably reduced during the next infection. The lifespan of memory cells ranges from a few months to a few decades.

Building the adaptive immune system takes time. Exposure to different environments, especially during childhood, introduces a variety of pathogens to the immune system, helping build a robust immune response later in life.

The Gut-Immune Connection

The majority of our immune cells are located in the gut (70-80%). The digestive tract is a long tube that is exposed to the outside world. It is monitored by immune cells within the mucosal lining, regulated by the gut microbiome - a diversity of resident bacteria that monitor the internal environment and influence how the immune system responds to threats.

Can We Really 'Boost' Immunity?

The immune system is a complex network of intercommunicating parts that work together tirelessly to keep us healthy - does it really need a boost?

Immune activation is highly regulated: too much, and we may get allergies (reactivity to harmless substances) and autoimmunity (immune activation towards our own body); too little, and we may experience frequent, more debilitating infections. The ultimate goal is to strike a balance by supporting the immune system rather than controlling it.

How do we support the immune system?

Nutrition

The immune system requires adequate energy, protein, vitamins, minerals, and essential fatty acids to produce immune cells, antibodies, and other compounds involved in defending the body against infection.

Protein is particularly important because immune cells and antibodies are made from amino acids.

Vitamins and minerals—including vitamins A, C, D, and E, zinc, selenium, iron, and B vitamins—also contribute to various aspects of immune function, from maintaining protective barriers such as the skin and gut lining to supporting communication and activity between immune cells.

A nutrient-dense diet rich in vegetables, fruits, legumes, whole grains, nuts, seeds, and quality protein sources can help provide the nutrients needed for optimal immune function. Fibre-rich foods and fermented foods are valuable for supporting a diverse and healthy population of beneficial gut bacteria.

Sleep

During sleep, the body supports the production and activity of immune cells and signaling proteins that help identify and respond to potential threats. Adequate sleep also helps regulate inflammation, allowing the immune system to mount an effective response without remaining excessively activated.

Research has linked insufficient sleep to reduced activity of certain immune cells and increased susceptibility to common infections.

Sleep is also essential for recovery. During periods of illness, infection, or physical stress, the body often requires more rest as immune activity increases. Prioritizing consistent, high-quality sleep—generally around 7–9 hours per night for most adults—is therefore one of the most important lifestyle strategies for supporting immune resilience and recovery.

Stress Management

When the body is under ongoing psychological or physical stress, stress hormones such as cortisol can alter immune signaling and, over time, may impair the body’s ability to mount an effective immune response. Chronic stress is also associated with increased inflammation, slower recovery, and greater susceptibility to some infections.

Effective stress management is an important component of supporting overall immune function. Regular physical activity, adequate sleep, mindfulness or meditation, deep breathing, time outdoors, and maintaining supportive social connections can all help regulate the body’s stress response.