The hidden role of immunity: it affects intelligence, depression and Alzheimer’s disease

When we talk about immunity, we usually think of immune cells fighting viruses, bacteria or other “invaders”. But immune cells have many other functions in our bodies and can determine, among other things, the health of our brains and the risk of diseases that affect the brain.

For the brain to function properly

While there are quite a lot of immune cells in the meninges, there are relatively few in the brain tissue itself compared to the rest of the body. Nevertheless, they play a very important role, not only in defence against infections, but even in brain development.

The most abundant immune cells in the brain are microglia, which make up about 80% of the brain’s immune cells. (To be more precise: while some experts consider microglia to be immune cells, specifically a type of macrophage, because they have been shown to participate in immune processes, others classify them more as nerve cells.) In addition, there are myeloid cells, macrophages, B cells, T cells, NK cells, dendritic cells, etc.

T cells in particular play a very interesting role here, as they are involved in a number of complex brain processes, including spatial learning, memory, emotional behaviour and memory. Microglia, in turn, regulate the number of neural stem cells and also influence the processes of myelination, synapse formation (the interconnection of neurons) or the formation and maintenance of small cerebral blood vessels. Not only the innate part of immunity is involved in the developmental processes of the brain, but even the acquired part.

Dangerous infections in pregnancy

Immune cells play the most important role in brain development and function during intrauterine development. It is even true here that infection of the mother during pregnancy can significantly affect the development of her child’s brain and the risk of psychological and neurological problems later in life.

For example, epidemiological studies have shown a link between infection and the development of depression, anxiety, autism, epilepsy, schizophrenia and even cerebral palsy. Several studies have also shown a strong relationship between infection in early childhood and the development of schizophrenia later in life, and there is also evidence of an association between early infections and memory and learning ability.

According to some theories, the increased incidence of psychological problems in recent decades may even be due to paradoxical medical advances – while many infections in pregnancy or early childhood were fatal before the spread of antibiotics, most infected people survive today, but the illness can affect brain development to some extent.

The enemy called inflammation

Another important function of immune cells is the secretion of substances called cytokines and chemokines. We usually associate the former in particular with the onset of inflammation, which is also true in the context of the brain – in fact, higher intensity inflammatory processes are found in virtually all brain-related disorders, from depression, to ADHD, autism, and Alzheimer’s disease.

Cytokines are usually secreted not only in response to infection but also in any other disturbance of the balance within the brain. The cause of their increased secretion can be, for example, trauma, stroke or neurodegeneration. People suffering from post-traumatic stress disorder have increased levels of cytokines (as well as lower levels of T cells and different levels of gene methylation), as do those with schizophrenia. Animal experiments have even shown that when cytokines are injected into their brains, their behaviour is severely impaired.

However, cytokines can also affect cognitive processes – for example, they impact synaptic plasticity, or the ability of nerve cells to form interconnections, which is crucial for memory or learning. They have a significant effect on nerve cells called astrocytes, which are involved in the formation and maintenance of interconnections between neurons. A single astrocyte affects more than 2 million synapses!

However, it must be said that both too high levels of certain cytokines in the brain and too low levels play a negative role in this regard.

Can a virus trigger Alzheimer’s?

Of course, immune functions are not only involved in the development of the brain during intrauterine development and childhood, but can also influence its fitness throughout the rest of life.

The most abundant immune cells in the brain – microglia – also play a key role in this regard. Their impaired function is probably involved in the development of Alzheimer’s, Parkinson’s and Huntington’s diseases, as well as in processes related to brain ageing. In addition, microglia have a very long lifespan compared to other immune cells, so the effects of any damage to them can be felt over a long period of time.

Do not let harmful substances into the brain

The blood-brain barrier, or the tight connection of cells separating the bloodstream from the brain, also plays an important role. When it is functional, it prevents not only pathogens but also many potentially harmful molecules, including a large number of inflammatory cytokines, from entering the brain. Some cytokines also increase the permeability of the blood-brain barrier. Thus, if the body experiences increased cytokine production, whether as a result of infection or tissue damage (e.g. due to trauma, stroke, etc.), this is followed by increased passage of cytokines and other harmful substances from the bloodstream into the brain, further impairing its function.

Indeed, the increased intensity of inflammatory processes is typical for most brain-related disorders. In addition, as we age, the level of inflammation in the body generally increases, and with it the risk of a number of diseases and disorders, be it mental illnesses such as depression and anxiety, or the development of neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease.

In addition, there is evidence supporting the “immune theory” of neurodegenerative diseases, i.e. that a viral or other infection may have been at the origin of Alzheimer’s disease. Cytokines produced by immune cells promote, among other things, the formation of amyloid beta (the substance that forms the plaques that coat nerve cells in Alzheimer’s disease) and its ability to aggregate. In turn, T cells, microglia and some other immune cells help to reduce beta-amyloid plaques.

However, stress can also play a big role in the fitness of our brains – stress hormones affect the functioning of the immune system, and this can in turn affect brain development and function.

5 steps to support your brain and immunity

Research into the link between immunity and brain development and function is still in its early stages. Not only do immune cells and the cytokines and other substances they secrete affect nerve cells directly, but they also interact with a number of substances that have a significant impact on brain development and function – for example, sex hormones, leptin, insulin… In addition, another powerful player comes into play in the form of the balance of the gut microbiome.

For this reason, it is not even possible to say exactly how to support immunity to work in favour of our brain. But here are a few steps that are proven to support both immunity and the brain. They can help us eliminate the negative impact of immune processes that affect our brains in adulthood, and perhaps even alleviate to some extent problems that originate in our early childhood.

So what can you do for your brain and immunity at the same time?

Support mitochondria

Mitochondria are cellular organelles in which nutrients are converted into energy. Both brain and immune cells are extremely energy-intensive, and when mitochondria are deficient or damaged, their function is significantly impaired. The number and condition of mitochondria is thus crucial for both immunity and brain function. It is no coincidence, then, that mitochondrial dysfunction is present in most brain-related problems, whether it is ADHD, autism, depression or even Alzheimer’s disease.

And how to support mitochondria? Regular exercise is essential, especially aerobic exercise – even low-intensity exercise, such as walking, is enough. Protection against free radicals, which damage mitochondria, care for the gut microbiome and a healthy diet are also important – a high consumption of simple sugars is particularly harmful.

More about mitochondria here ‘

Take care of your gut microbiome

The influence of the gut microbiome on the state of immunity is quite crucial. For example, some of the gut bacteria are involved in controlling the maturation of the immune system, the production of individual immune cells and immunoglobulins (i.e. antibodies). Proper diversity (variety) of gut microorganisms also helps create immunoregulatory networks that protect us from developing allergies. Immediately after birth, so-called Toll-like receptors are also formed in the mucosa, which respond to signals sent by microbes during infection and subsequently help trigger an immune response. Read more ‘

But the connection between the gut microbiome and the functioning of our brain is equally strong. Its balance influences, for example, the level of inflammatory processes in the whole body, including the brain. Some gut bacteria also produce a fatty acid called butyrate, which is crucial for the functioning of the mitochondria of nerve cells or the production of BDNF, which is needed for the entry and protection of neurons. Disrupting the balance of the gut microbiome can thus lead to impaired cognitive performance, mood or social behaviour disorders, as well as accelerating brain ageing. Read more ‘

Consumption of fibre is crucial for the balance of the gut microbiome. Dietary polyphenols, a diet rich in omega-3s, as well as limiting food additives, alcohol, excessive consumption of simple sugars or saturated fats can also help.

Fight inflammation

Acute inflammation is an important process that helps us fight infections or injuries, while chronic inflammation is a problem that contributes to many diseases. Chronic inflammation has a completely negative effect on the brain (see above), and although immune cells are involved, it also compromises our body’s defences.

Diet is especially important for fighting inflammation. Especially the influence of excessive carbohydrate consumption is harmful here. In research, even a small increase in sugar consumption (50 g) led to a significant increase in the intensity of inflammation. On the other hand, increasing the intake of omega-3 (and adjusting their ratio to the consumed omega-6 unsaturated fatty acids), olive oil, polyphenols from fruits and vegetables…

Read more about how to fight inflammation here ‘

Maintain optimal weight

Obesity significantly increases the level of inflammatory processes throughout the body, including the brain. It has a significant negative effect on the activation of immune cells and alters the levels of some of them. The so-called central obesity, i.e. a higher proportion of internal or visceral fat, has a significantly worse effect.

Large epidemiological studies have also shown a negative association of obesity with mental performance. Obesity in middle age also increases the risk of dementia in older age.

Maintaining an optimal body weight is such an important step in supporting both the immune system and the health of our brains.

Try dietary supplements

A number of epigenetically acting nutrients and herbs have a significant positive effect on both brain and immune system function. Here are some of them.

St. John’s wort – a herb also known as astragalus effectively supports the function of the blood-brain barrier, slows down brain aging, protects nerve cells in the cerebral cortex and hippocampus (seat of memory) and counteracts the formation of beta-amyloid plaques. It can influence both innate and acquired immune responses, as well as the formation, development and activation of a wide range of immune cells, such as monocytes, macrophages, T-cells, B-cells and dendritic cells. It also increases the production of IgA, IgG and IgM antibodies and has a significant anti-inflammatory effect.

Hydroxytyrosol – a polyphenol abundantly contained in olives is one of the most powerful natural antioxidants and has a strong anti-inflammatory effect. It improves the overall immune response and the production of a number of immune cells, and has direct antiviral and antibacterial effects. Its positive effects on the brain are also extensive, which is due to its ability to penetrate the blood-brain barrier and act directly in brain tissue. There, it mitigates nerve cell damage, improves cognitive function and slows its decline with age, and reduces the risk of Alzheimer’s disease.

Resveratrol – a dye from red wine has a significant positive effect on memory and cognitive processes. It also protects nerve cells from damage and stabilises amyloid levels in the brain. It has a strong anti-inflammatory effect and is one of nature’s most powerful activators of sirtuins, which are age-slowing enzymes that are also essential for proper mitochondrial function.

Rhodiola – has a positive effect on virtually all cognitive abilities, repairs damage to the blood-brain barrier, counteracts depression and anxiety, and also alleviates the negative effect of fatigue and stress on mental performance.

Butyrate – a short-chain fatty acid is essential for the proper functioning of the brain. It is normally produced by intestinal bacteria, but when the gut microbiome is disrupted, it can be used as a dietary supplement. According to studies, it can be beneficial for all brain-related problems (memory and learning disorders, autism, ADHD, depression, Alzheimer’s disease and other types of dementia, insomnia, depression, and more).

Saffron – the scales of the crocus are known primarily for their antidepressant effects, which are comparable to antidepressants for moderate depression (and can also be combined with these drugs). But it also has a direct positive effect on mental performance and memory, reducing the negative effect of stress on cognitive processes and preventing the formation of beta-amyloid plaques. It also supports the ability of the gut microbiome to produce butyrate.

Baikal coneflower – has a very strong anti-inflammatory effect and directly supports immunity and acts against some viruses and bacteria. It can alleviate memory disorders caused by beta-amyloid plaques (i.e. in Alzheimer’s disease), improves mitochondrial function in brain tissue and a number of cognitive functions, and supports the resistance of nerve cells to oxygen deprivation and ageing-related processes. It effectively supports the integrity of the blood-brain barrier, but some of its active substances can also penetrate the barrier and act directly inside the brain.

Quercetin – it is a very powerful antioxidant with anti-inflammatory and epigenetic effects, which also has a positive effect on the intestinal microbiome and mitochondrial function. It is also able to penetrate directly into the brain, while protecting the blood-brain barrier.