Written by Dr. Inez Van Roy on
June 29, 2021
Reading Time: 8 minutes

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Written by Dr. Inez Van Roy on:

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Written by Dr. Inez Van Roy on:
June 29, 2021

Brain fog is a common feeling of grogginess, being forgetful, not thinking clearly or even feeling like you are mentally “foggy.”

But what causes brain fog? More than just a lack of sleep, brain fog can have many causes and in this blog post I’ll be going over 9 different potential reasons why you might be experiencing it. From anxiety to vitamin deficiencies, let’s break down some of the most common causes for brain fog that entrepreneurs who are also mothers experience.


What is brain fog?

Brain fog is not a condition or a disorder. That means we can’t diagnose brain fog. But we can recognize this symptom cluster. People use this to describe a variety of problems like poor concentration and bad memory. Some also report difficulties with logic and problem solving. 


This cloudy mist in your head usually is a symptom that points to another medical condition. Recognizing the cause of this, means that you don’t have to live with the haziness.

1. Dehydration

Your brain is mostly made of water. Roughly 75% to 85% of the mass is from water, and it accounts for about 50 to 75% of your total body weight.

When you don’t drink enough water your body will not be able to function properly. A dehydrated brain could be a foggy brain. 

There are many reasons why people get dehydrated. They forget to drink, their diet lacks fluids. Sometimes an illness like the flu is the culprit. Having a fever and losing fluids because of sickness could cause dehydration. 

Elderly and children are more sensitive to dysregulation in their hydration levels. Research shows that even mild dehydration (only 1 to 2%) already declines your cognitive performance

Dehydration could also impact your mental health. Your mood and anxiety levels might take a hit. Dehydrated people have more difficulty concentrating. They have a slower reaction time and score worse on short-term memory tasks.

2. Vitamin deficiency

I. Low levels of Vitamin B12

Vitamin B12 is a nutrient that is necessary for creating healthy red blood cells. It is vital in supporting a normal central nervous system

A deficiency in this vitamin can cause megaloblastic anemia, and can lead to nerve damage. If you have a shortage of B12, your body might not have enough red blood cells to carry oxygen through your body. 

Elderly and people with Crohn’s disease or Celiac sprue syndrome, are often at risk for vitamin B12 deficiency. This is because their body doesn’t absorb these nutrients that well. As a result of these cognitive troubles they have a higher chance of false diagnosis. Doctors sometimes interpret it as Alzheimer’s disease, due to age. 

Vitamin B12 can be mostly found in animal products.  

Vegetarians or vegans should keep a close eye on their levels and supplement if needed.

II. Iron deficiency

Iron plays an essential role in transportation and production of oxygen. This mineral is essential for a correct working brain and central nervous system. It aids in neurotransmitter production, neuroprotection and other activities.

A shortage of iron usually accompanies problems with executive functions (f.e. Planning, organisation), attention and mental fatigue. 

Causes of iron deficiency are again related to how you eat or how you absorb this mineral. A vegetarian or incomplete diet is a risk factor. Celiac disease can cause malabsorption. Lastly, heavy blood loss is also a culprit of iron deficiency.

Your medic can check your levels of iron with a blood test.

3. Toxins

I. Heavy metal exposure

Arsenic, cadmium, chromium, lead, and mercury are highly toxic heavy metals for us humans. Symptoms are dependent on the heavy metal, the amount and the time frame in which they are ingested. 

Cancer, cardiovascular diseases, hematologic and immunologic disorders have an association with heavy metals. They are known to be neurotoxic

These toxins are all around us in industrial and agricultural use, they might be in our soils, food and plastics.

If you suspect heavy metal poisoning, it is recommended to get your blood tested by a doctor who specialises in this area of medicine.

4. Hormonal changes 

I. Menopause

Perimenopause is the period of time before menopause which can last about ten years. Menopause is defined as a period in which you don’t have your period for 12 months. Further you can also expect vaginal dryness or discomfort during intercourse. 

During menopause your mental health might also decline. Anxiety and depression is more common during these times.  Brain fog for people in menopause comes with complaints of memory, concentration. Fingers point mostly to the decline of estrogen for these complaints.

II. Pregnancy

Pregnancy and premenstrual syndrome can all lead to hormonal changes that affect brain function. Women and their partners complain about the “mommy brain” or “pregnancy brain”. A stark hormonal change (and strong fatigue) could be the root cause of their brain fog. Research shows there is a relevant difference in memory performance. These women complain of concentration problems, memory decline and absentmindedness.

III. Underactive Thyroid

Hypothyroidism is a condition of the thyroid gland. It produces an inadequate amount of thyroid hormones. Physical symptoms are dry skin, weight gain or loss and heart-related problems. Other consequences are fatigue, depression and forgetfulness. 

Brain fog is also one of these symptoms. Treatment for an underactive thyroid could be hormone replacement therapy or a change in diet.


5. (Chronic) illness

I. Lupus

Lupus  (or systemic lupus erythematosus, SLE) is a chronic autoimmune disease. It is a disease in which your immune system attacks its own healthy cells.  Usual symptoms are joint pain, butterfly rashes or extreme fatigue. Patients or doctors usually speak about lupus brain fog. Cognitive symptoms of lupus fog are in general:

  • sleeplessness
  • rushed speech
  • difficulty with word finding
  • difficulty navigating
  • trouble remembering small details
  • impairment of other brain functions

II. Multiple Sclerosis (MS)

Multiple sclerosis is a disease of the central nervous system. It interrupts and damages nerve cells in the spinal cord. MS leads to problems with movement or thinking. 

Patients may experience cognitive symptoms from MS-brain fog like: 

  • lack of concentration, 
  • attention deficit disorder (ADD), 
  • depression, 
  • memory loss, 
  • slurred speech 
  • and vision impairment.

III. Cancer

Cancer and the consequences (f.e. Chemo or other cancer treatments) can cause brain fog. The disease is also a cause for stress, lack of sleep, hormonal changes and a change in diet. All those can be contributing factors to your brain health.

IV. Chronic Fatigue Syndrome (CFS)

Chronic Fatigue Syndrome (CFS) is a condition characterized by long-term fatigue. This fatigue has no other medical explanation. If you experience these symptoms and brain fog, you might have CFS. 

IV. Fibromyalgia

Fibromyalgia is a chronic illness characterized by musculoskeletal pain, tenderness and fatigue. Their central nervous system has a problem with pain processing. Fibromyalgia can also cause brain fog, or fibrofog as some say. Fibrofog comes with loss of mental clarity (mental fogginess), attention and memory impairment.

Postural tachycardia syndrome

Postural tachycardia syndrome or POTS is a disorder of the autonomic nervous system. POTS usually shows itself in fainting and lightheadedness from a horizontal position. They also experience a sudden rapid heartbeat with these symptoms.

Patients with POTS believe that these are the most common causes of their brain fog:

  • fatigue,
  • lack of sleep,
  • prolonged standing,
  • the feeling of fainting
  • and dehydration.

V. Alzheimer’s disease

Alzheimer’s disease is an irreversible, progressive brain disorder. It slowly destroys memory and thinking skills. There is a buildup and accumulation of plaques and proteins in the brain where it shouldn’t be. Short term memory problems, like remembering recent events or familiar faces, are common in the early stages of Alzheimers.

As symptoms progress, patients become less able to carry out daily tasks independently. They might need help dressing themselves or preparing meals. Brain fog could be  an early sign of this disorder. If you have family history and are older than 65 years, it would be good to check this out with your doctor.

VI. Obesity

The American Medical Association labels obesity as a disease. Overweight or obese people have an increased risk of heart attack, high blood pressure and type II diabetes.  What’s more, it can cause changes to your mood (such as depression) and brain fog. Researchers believe that the brain fog in obesity might be due to a focal brain inflammation.

I. COVID – 19

COVID-19 is a disease caused by the SARS-CoV-2 virus. It is usually described with symptoms of fever, shortness of breath and coughing. However, many other symptoms show up in this disease. People with long COVID-19 or “long haulers” also describe brain fog as a long-term consequence.  


6. Medication

I. Chemotherapy

Chemo brain (also called chemo fog) can occur during and after cancer treatment.

The term chemo brain and the symptoms are widely used and known. Yet, we still don’t know the cause of these cognitive problems and dysfunctions.


7. Allergy medications

Not only the medication but als the allergy can give you a fuzzy feeling. Allergy is an extra active immune system. Many times doctors prescribe an antihistamine to combat this reaction. Antihistamines are known to be a sedative. Feeling drowsy or sleepy in your brain is to be expected. Other medication might also be to blame, talk with your doctor to figure out if that might be the case.

8. Drugs & alcohol

Drug use and alcohol is known to be neurotoxic and can lead to changes in the brain that result in brain fog. Getting sober can clear up the brain fog after a while.

9. Mental illness or stress

I. Stress

This one should be on everyone’s list. It can take a toll not only on our health but also on your relationships with family members or friends. Stress causes a depletion of certain neurotransmitters. This has a big impact on how we think and feel -or rather don’t feel- at all. Stress has a large impact on your cognition. It could lead to:

  • short attention span,
  • reduced concentration levels,
  • depression
  • memory problems
  • and difficulty making decisions.

II. Depression

Depression is a mood disorder in which people feel constantly sad and apathetic. They might have no more interest in life or the world around them. Cognitive symptoms can be concentration problems and a general slowness and fatigue.

III. Anxiety

Anxiety is a normal reaction of our body to survive. People who have an anxiety disorder have a constant fear or worry about life that might pair with panic. Anxiety might come with symptoms such as trouble concentrating or brain fog.

10. Sleep

Not getting enough sleep has negative impacts on your quality of life. Your daily functioning, mood and cognitive performance will suffer as well. What’s more it may cause or worsen mental health problems such as depression.

Sleep deprivation leads to an excessive release of stress hormones (such as cortisol). These are neurotoxic in large amounts for the brain. Long-term exposure to inadaptado stress levels will affect memory consolidation and emotional stability. 

How do you get rid of brain fog?

Talking to your doctor to diagnose the cause of your brain fog is a first step! Lifestyle changes can help your immune system and support healthy brain function. A doctor can order a blood test to check nutrient deficiencies or toxins in the blood. 

The advice would be to eat a healthy diet and include regular exercise. Poor diet, food allergies or sensitivities can upset your digestive system and lead to nutritional deficiencies. It is shown that a diet with enough iron, healthy fats and whole grains is good for you. Further it is recommended to get the full 7 or 8 hours of sleep, get enough fluids (two to three liters) and reduce stress.  Certain medications can help, however this should be discussed with someone with medical expertise. Only doctors can provide medical advice.


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