What causes Brain Fog?

Introduction

The cause of brain fog is a mystery because the symptoms are so varied.

There may be one or several contributors to ‘Brain Fog’, however the exact underlying cause in relation to Covid-19 is the subject of ongoing research.

Some potential post Covid-19 causes and contributors can include:

Primary and Organic Contributors

Post-Viral Fatigue

Fatigue, or excessive tiredness, is common after viral infections and can affect your ability to concentrate. You may feel that you don’t have the mental energy needed to pay attention to things, even when you think something is important. If you can’t concentrate on something, it is harder to remember it. It may be difficult to concentrate on work tasks, especially the less interesting tasks, as trying to concentrate can feel exhausting.  

Lingering Covid-19 virus/viral debris

The Covid-19 virus has been shown to cause direct infection of proteins found in the brain stem, cerebellum and cranial nerves (known as Neurotropism). This is similar to the pathological process which occurs in Alzheimer’s Disease. 

Inflammation of the Brain (Encephalitis)

In a small number of people, Covid-19 can cause inflammation in the brain. Research, so far, indicates that, when a person is infected with Covid-19, the body’s immune system can over-react causing a hyper-inflammatory response which results in it attacking normal, healthy cells, including those in the brain. A storm of excess cytokines (molecules released by the body’s immune system to fight off infection) can seep into the area around the brain because the protein in the brain is similar to the viral proteins that the immune system would usually attack. This can cause brain inflammation inducing the death of the brain cells required for effective cognitive function. The specific effects depend on which part(s) of the brain have been affected.

Insufficient Oxygen Supply to the Brain (Hypoxia)

Some people with COVID-19 experience breathing problems caused by severe inflammation of the lungs called Acute Respiratory Distress Syndrome (or ARDS). Patients who develop ARDS are usually admitted to intensive care and often their breathing is supported by a mechanical ventilator. The brain is highly dependent on oxygen and if oxygen levels remain low for a period of time it can result in damage to the brain. The effects on memory and thinking will depend on which parts of the brain are involved.  

Insufficient Blood Supply to the Brain (Ischaemia)

A small proportion of people suffer a stroke a result of having Covid-19, caused by insufficient supply of blood to the brain. If you were one of these your healthcare team will have informed you. Although it is rare, Covid can affect blood vessels, causing blood Produced by Kay Richardson, Occupational Therapist Salford Post-Covid Rehabilitation Service clots to form which travel to the brain and interrupt blood flow to a specific part(s) of the brain. The consequences of this depend on which part of the brain is affected, but could include physical, cognitive or emotional problems.

Microvascular Damage

Covid-19 has been shown to affect microcirculation (microcirculation is the network of arteries, arterioles, capillaries and venules that supply and drain blood from every tissue and organ in the body). This can cause endothelial cell swelling and damage (endotheliitis), microscopic blood clots (microthrombosis), capillary congestion, and damage to pericytes (important for blood vessel formation, maintenance of the bloodbrain barrier, regulation of immune cell entry to the central nervous system and control of brain blood flow) – (Ostergaad, 2021). 

Covid-19 related microvascular damage and inflammation may cause tissue hypoxia as well as disturbing neurotransmitter synthesis within the brain. This can impact on the appropriate distribution of oxygen, glucose and other nutrients by the cerebral vasculature which is critical for proper cognitive performance. 

Dysfunction of the endothelial cells (cells in blood vessel/tissue lining responsible for vascular relaxation and contraction, blood clotting, immune function and platelet adhesion), has also been associated with cerebrovascular damage and cognitive decline.

Heart Inflammation/Damage

There are three main types of heart inflammation: endocarditis, myocarditis, and pericarditis. Endocarditis is inflammation of the inner lining of the heart’s chambers and valves. Myocarditis is inflammation of the heart muscle. Pericarditis is inflammation of the tissue that forms a sac around the heart. Many things cause heart inflammation. Common causes include viral or bacterial infections and medical conditions that damage the heart and cause inflammation. Heart failure (HF) following heart damage leads to a decreased blood flow due to a reduced pump efficiency of the heart muscle. A consequence can be insufficient oxygen supply to the brain.  

Mast Cell Activation Syndrome (MCAS)

There are three main types of heart inflammation: endocarditis, myocarditis, and pericarditis. Endocarditis is inflammation of the inner lining of the heart’s chambers and valves. Myocarditis is inflammation of the heart muscle. Pericarditis is inflammation of the tissue that forms a sac around the heart. Many things cause heart inflammation. Common causes include viral or bacterial infections and medical conditions that damage the heart and cause inflammation. Heart failure (HF) following heart damage leads to a decreased blood flow due to a reduced pump efficiency of the heart muscle. A consequence can be insufficient oxygen supply to the brain.  

Breathing Pattern Disorder or Dysfunctional Breathing

Dysfunctional breathing is a term that relates to a change in breathing pattern from an efficient to less efficient pattern. Triggers can include acute illness or infection and it is a common occurrence following Covid-19.

Efficient breathing tends to involve nasal inhalation which is automatic, effortless, relaxed, quiet and steady. This type of breathing will usually reach your diaphragm and you will see tummy movements. Inefficient breathing tends to involve mouth inhalation with short, shallow, quick and erratic breaths. It also tends to be noisy and can cause tension in the shoulders. This type of breathing tends to involve movement at the top of the chest only and may feel like panting or hyperventilation. 

In a study by Zelano et al in 2016, the way we breathe has been shown to have an impact on certain areas of brain activity. During inhalation, neurons in the olfactory cortex, amygdala and hippocampus (the areas responsible for emotions, memory and smell) are stimulated.

Persistent Loss of Smell

Loss of smell has been linked to ongoing dementia-like symptoms in those who had a
positive test for Covid-19 and persistent loss of sense of smell can be a predictor of
cognitive impairment. In a study by Professor de Erausquin, around 34.4% had signs of
multi-domain cognitive impairment including severe short term memory, semantic
memory (ability to recall a word, concept, number), executive function failure and
reduced attention. The severity of this cognitive impairment correlated with a persistent
loss of sense of smell, rather than the severity of the acute infection. Covid-19 has also
been found to be present inside the cells of the olfactory epithelium up to 6 months after
initial infection. Proteins found along the olfactory tract and bulb within the brain
suggest this could be a possible route for the virus to infect the brain.

Diabetes

Cases of new Type 2 diabetes diagnoses have been reported in some people who have had Covid-19. Diabetes is a chronic disease which happens when your blood glucose, also called blood sugar, is too high. This could be related to the direct effects of coronavirus on the body, or the effects of lifestyle changes due to the pandemic. 

Glucose is the main form of energy for the brain. In diabetes, there is a problem with both glucose and insulin that leads to a host of problems. Glucose needs insulin to enter the cells, but in diabetes either the body can’t make insulin, doesn’t make enough, or can’t use its insulin correctly. As a result, glucose remains in the bloodstream and accumulates. High blood sugar (hyperglycaemia) does extensive, system-wide damage. Low blood sugar (hypoglycaemia), a result of diet and/or medication, also causes damage. These blood sugar problems impair functioning in the brain and can cause brain fog and memory loss. 

Blood sugar fluctuations affect neurotransmitter levels. High blood sugar increases serotonin and GABA, causing fatigue. Low blood sugar causes the brain to release more Cortisol, Glucagon, and Adrenaline in an attempt to counteract hypoglycaemia. Stress increases, and concentrating and focusing become more difficult. 

Blood sugar highs and lows also create problems with blood circulation. Restricted circulation to the brain starves it of nutrients and oxygen. The brain can’t function at its peak when it lacks nourishment; therefore, symptoms of brain fog begin.

Hyperglycaemia damages vessel walls over time, reducing their flexibility and responsiveness to the blood flow within them. In the brain, blood vessels need to flex to accommodate changing circulation. The brain adjusts the amount of blood it uses to support the functioning of various areas and structures. When blood vessels are rigid, they don’t move fluidly to supply nutrients and oxygen where they’re most needed.  

Other Medical Contributors:

  • Chronic Infection (viral, fungal or bacterial)
  • Dysautonomia
  • Anaemia
  • Hormonal Imbalances
  • Menopause/Peri-Menopause
  • Thyroid Issues – Hypo/Hyperthyroidism
  • Migraines
  • Sleep Apnoea
  • Other Medical Conditions such as Sjogren Syndrome, Alzheimer’s Disease, Lupus,
    Multiple Sclerosis, Arthritis and Dehydration.

Medical investigations via GP should be completed to rule out any potential medical causes/diagnoses contributing to symptoms of ‘Brain Fog