Nutrition and your immune system

As the COVID-19 episode (or possibly, fiasco) rolls on, many clients and subscribers are asking me if there’s anything they can do to boost their immunity against the virus.

It’s an understandable question in the current climate of terror and panic, which is being fed by sensationalist reporting and is not being set in the context of the estimated 250,000–500,000 deaths worldwide that are attributed to influenza-like-illness, and which are in fact associated with a plethora of viral and bacterial pathogens, including coronaviruses.

However, this question betrays a fundamentally reductionist understanding (or more accurately, misunderstanding) of health.

Unfortunately, the concept of health is foreign to orthodox medicine, which focuses instead on ‘fighting disease’ with an arsenal of pills and procedures. In industrialised countries, and increasingly in developing countries, the vast majority of medical interventions are aimed at managing the downstream consequences of living in a way that is not conducive to human health (think coronary artery bypass grafting, medications for high blood pressure and type 2 diabetes, and bariatric surgery).

But there is no true immunity without health. Research clearly shows that our state of health, and specifically our nutritional status, is the primary determinant of whether we will contract viral infections like COVID-19 or influenza (as well as bacterial infections) in the first place, and how severely they will affect us.

However, in a healthy organism, symptoms of disease will inevitably emerge from time to time in an organised effort to restore health.

Confused? Read on!

Let’s start by taking a look at how the human immune system defends itself against pathogens such as viruses and bacteria.

Physical and chemical barriers

Intact skin provides an effective barrier to the entry of viruses and bacteria.

Mucous membranes such as those that line the respiratory and gastrointestinal tract aren’t so well sealed-off, so they secrete a variety of substances such as mucus, stomach acid, tears, enzymes and antimicrobial peptides such as immunoglobulin A, as well as initiating reflexes such as coughing and sneezing, to trap, destroy and expel pathogens.

Probiotics, or friendly bacteria living in our gut and genitourinary tract, also form a barrier to infection by competing for living space and nutrients, and secreting chemicals that kill or inhibit the growth of pathogens.

The innate immune system

If pathogens manage to sneak their way past all those barriers, they will encounter proteins called pattern recognition receptors (PRRs), produced by the cells of the innate immune system.

PRRs recognise particular components of bacteria and viruses, such as their RNA and DNA, lipopolysaccharides and lipoproteins.

PRRs also respond to distress signals sent out by cells that have been damaged or injured by infection.

Once the innate immune system is triggered, a wave of chemical and cellular activity is unleashed against the intruder:

• Inflammatory chemicals are released in order to increase blood flow to the infected area and make blood vessels more permeable, so white blood cells can squeeze out of blood vessels and into infected tissue. It’s this inflammatory response that causes symptoms such as sore throat and fatigue.
• Pyrogens including interleukin-1 and interleukin-6 drive up body temperature, resulting in fever.
• Leukotrienes attract white blood cells, the body’s infection-fighting cells.
• Interferon is released, to shut down protein synthesis in virus-infected cells, thereby limiting the spread of the virus.
• The complement system, comprising over 20 different proteins, is activated to assist the action of specific antibodies against the pathogen.
• White blood cells including phagocytes, mast cells and natural killer cells are constantly on duty, patrolling the bloodstream in search of invading pathogens.
  When they receive their ‘call to arms’ from the numerous chemicals secreted as part of the innate immune response, their activity level dramatically increases and they rush to the site of infection.
  They destroy smaller pathogens by engulfing and digesting them with powerful enzymes; larger ones are irreversibly damaged when white blood cells attach to their cell membranes and perforate them.
• Dendritic cells, a subtype of phagocytes, play a bridging role between the innate and acquired immune system by presenting antigens (the ‘calling cards’ of pathogens) to T cells, one of the primary cell types responsible for acquired immunity.

It is an astonishing fact that 80% of the innate immune system resides in the gastrointestinal tract, the primary point of contact between us and the outside world. Good gut health is vital to overall good health and resistance to infectious disease!

(Listen to my podcast interview Deep dive into gut health and read You are what your gut bacteria eat, Gut bugs and human health: A tale of two evolutionary trajectories and Fat chance of having a healthy gut for more information on cultivating a healthy gut microbiome.)

The acquired immune system

While the body’s physical and chemical barriers, and the innate immune system, provide formidable defences, these systems have no ‘memory’ of previous intruders. Each battle to repel invaders is conducted without the benefit of having learned that particular enemy’s weak points.

The acquired immune system, comprising white blood cells known as lymphocytes, ‘remembers’ invaders through their signature antigens (unique proteins that are found on the surface of the pathogen, or displayed by a virus-infected cell), enabling it to mount a much faster and more powerful immunological response should that pathogen ever invade again.

T cells and B cells are the major types of lymphocytes.

Each T and B cell carries a receptor molecule that allows it to recognise only one specific antigenic target.

T cells are involved in cell-mediated immunity. Killer T cells, assisted by helper T cells, recognise particular antigens displayed by cells which have been infected by viruses and other pathogens, or which have become damaged or dysfunctional (e.g. cancer cells).

They then release chemicals called cytotoxins which destroy the integrity of the membrane of the target cell and cause it to undergo apoptosis, or cell suicide.

B cells are involved in humoral immunity. Millions of naive B cells (mature B cells that have not yet been exposed to an antigen) circulate in the bloodstream, each of them only capable of recognising a single viral or bacterial antigen that the body they’re protecting has not yet encountered. Over 90% of them die without ever finding their designated antigen. (I hope they don’t feel that their life has been without purpose ;-).)

Once a naive B cell has been exposed to ‘its’ antigen, it enlarges into a plasma B cell, and begins secreting large amounts of antibodies – Y-shaped proteins which have a unique binding site shape that locks onto the specific shape of the ‘matching’ antigen. Antibodies travel through the bloodstream and lymphatic system, searching for pathogens or blood-borne viruses which bear the matching antigen.

The antibody binds to the antigen, marking the cell bearing it for destruction by the complement system or by phagocytes. Antibodies also bind to and inactivate bacterial toxins.

As the body proceeds to fight off the infection, memory B cells are formed from activated B cells. These reside in the bone marrow, lymph nodes, and spleen, and can survive for many years, even up to a lifetime.

When re-exposed to ‘their’ antigen, they rapidly become activated, forming a clone of plasma cells that release millions of antibodies, which neutralise the infection before symptoms even develop.

You are what you eat – and so is your immune system

Now let’s look at the impact of nutrition on the immune system.

Protein-energy malnutrition – found not just in the developing world but also right here in Australia among many of our elderly, and in sufferers of anorexia nervosa and many debilitating diseases such as cancer – has a devastating effect on each of these three tiers of immunity.

Cell-mediated immunity, phagocyte function, production of immunoglobulin A and antibodies, and the function of the complement system are all significantly impaired in people suffering from this kind of malnourishment.

The more common type of malnourishment in rich Western countries, however, is what has been called high-calorie malnutrition: overconsumption of foods that are deficient in micronutrients such as vitamins, minerals and phytochemicals.

Even relatively mild deficiencies of virtually any of these micronutrients significantly influence immune responses. For example:

• Both vitamin B6 (pyridoxamine) and folate deficiency reduce the number and the effectiveness of B and T lymphocytes.
• Vitamin A deficiency impairs the production of antibacterial compounds in tears, saliva and sweat; causes lymphoid tissue to atrophy; and reduces antibody formation.
• Deficiencies of iron, zinc and magnesium all increase susceptibility to infection (although an excess of iron has the same effect).

In addition to vitamins and minerals, a host of other plant-derived micronutrients known as phytochemicals (such as lutein, lycopene, bioflavonoids, and polyphenols) also modulate both our susceptibility to infectious disease, and the severity and outcome of such diseases.

In a fascinating demonstration of the interwovenness of plant and animal life, many of these phytochemicals are produced by plants to defend them from pathogen attack or insect predation.

For example, resveratrol (the powerful polyphenol found in red grapes, mulberries, peanut skins, rhubarb, and several other plants), is essentially part of the immune system of the plants that produce it. It is produced in much higher amounts by grapes under stress from poor soil and challenging climatic conditions, or during attack by fungal disease.

The same compound, at low concentrations achievable through dietary intakes, activates macrophages, T cells and natural killer cells (but be warned – in high doses, such as those delivered by supplements, it may suppress immunity).

But while nutritional deficiency has long been known to depress our immune function, there is an even more intriguing twist: Nutritional deficiencies directly interact with the genomes (DNA sequences) of pathogens themselves, making them more virulent.

Individuals whose diets are deficient in antioxidant vitamins, minerals and phytochemicals experience oxidative stress. This oxidative stress alters the genome of invading viruses, causing them to mutate into potentially more dangerous forms that result in more prolonged and serious infections.

For example, coxsackievirus B3 is normally quite benign, with infection causing only symptoms of the common cold. However, oxidative stress due to host deficiency of either vitamin E or selenium causes this virus to alter its DNA sequence to that of a virulent strain, and to become capable of causing heart damage.

Widespread dietary deficiencies of riboflavin, vitamin E, selenium, alpha- and beta-carotenes, and the carotenoid lycopene (as well as high smoking rates) in the Cuban population in the early 1990s are believed to have been responsible for coxsackie virus mutations that caused an epidemic of optic and peripheral neuropathy (visual and nerve problems).

Viruses can only replicate, and therefore can only mutate, when they are inside the cells of a living host. Our state of nutrition when we become infected, therefore, is the primary determinant of whether the virus will remain fairly benign or become much more virulent.

While a more virulent virus is undoubtedly more of a threat to us than a benign one, most of the immediately unpleasant symptoms (fever, sore throat, fatigue) and the serious and critical complications of SARS-CoV2-2 infection (respiratory distress and failure, shock, multiorgan dysfunction) are not directly due to the infectious organism itself but to our own immune system’s response to it; specifically, the release of inflammatory chemicals by the immune system.

It’s important to understand that this acute inflammatory response is crucial for overcoming infection. Fever is a case in point:

“The fever response is a hallmark of infection and inflammatory disease and has been shaped through hundreds of millions of years of natural selection… There is mounting evidence that the increase of 1 to 4°C in core body temperature that occurs during fever is associated with improved survival and resolution of many infections. For example, the use of antipyretic drugs [such as Panadol and Nurofen] to diminish fever correlates with a 5% increase in mortality in human populations infected with influenza virus and negatively affects patient outcomes in the intensive care unit.”

Now do you understand the statement I made at the beginning of this article about the symptoms of disease being part of an organised effort to restore health? The symptoms are part of the cure.

However, dietary antioxidant deficiency ramps up the inflammatory response, causing much greater tissue damage than occurs in a well-nourished individual.

Put simply, when we are deprived of anti-oxidant nutrients (found in greatest concentrations in whole plant foods), viral infections can cause serious, even fatal diseases, that don’t occur when deficiency is not present.

Unfortunately, a large proportion of our population is at increased risk of complications of viral infections because they are micronutrient-malnourished from insufficient consumption of unprocessed plant foods.

In addition, the chronic low-grade systemic inflammation which occurs as people get older, known as ‘inflammaging‘, generates increased pro-oxidant compounds.

Cigarette smoking also causes oxidative stress and chronic inflammation.

Now you can grasp why people who are elderly and/or have cardiovascular disease, diabetes, chronic respiratory disease or cancer are disproportionately affected by COVID-19 (along with the vast majority of other respiratory tract pathogens): all these conditions are associated with chronic inflammation and oxidative stress, which impair immune responses and increase the likelihood of complications of infection.

The diet I personally adhere to, and advocate to all my clients, emphasises a very high intake of fresh, raw or conservatively cooked fruits and vegetables, along with other antioxidant-rich plant foods. The same diet that prevents and often reverses chronic degenerative disease, and keeps you slim and young for your age, also protects you against acute viral infections – and for much the same reasons!

If you are overweight or have a chronic disease that puts you at increased risk of serious illness, NOW is the time to take action on it! Obesity, type 2 diabetes, hypertension and coronary artery disease are preventable and largely reversible with a wholefood plant-based diet and Lifestyle Medicine. Apply for a Roadmap to Optimal Health Consultation today; online appointments are available for those practising social distancing.