Do you struggle to concentrate at work, find it difficult to stay focused on everyday tasks, or feel as though your brain is working more slowly than usual? Perhaps you feel mentally tired even when you have had enough sleep, or find yourself easily distracted and unable to think clearly.
These experiences are often described as brain fog, and they can affect people of all ages.
Brain fog, poor concentration and difficulty focusing can have many possible causes, including poor sleep, stress, nutritional deficiencies, thyroid problems and changes in blood glucose. Sometimes, several factors may be contributing at the same time.
While blood tests cannot diagnose brain fog itself, they can help identify certain underlying health issues that may be affecting your energy levels, concentration and mental clarity.
At Mybloods, we believe that understanding your health starts with having the right information. In this guide, we explain what brain fog is, what may cause it, which blood tests may be useful
What is brain fog?
Brain fog is a general term used to describe difficulties with mental clarity, concentration and thinking. It is not a medical diagnosis, but it can be a symptom of an underlying health issue or a response to lifestyle factors.
People experiencing brain fog often describe feeling mentally sluggish, distracted or less sharp than usual.
Common symptoms include:
Difficulty concentrating on work, reading or conversations.
Struggling to stay focused on one task.
Feeling mentally tired or overwhelmed.
Finding it harder to process information.
Becoming easily distracted.
Difficulty organising thoughts or making decisions.
Feeling less productive than usual.
Experiencing a general sense of mental sluggishness.
Brain fog can be occasional or persistent. Some people notice that it becomes worse during periods of stress, poor sleep or hormonal changes, while others experience it alongside physical fatigue or other symptoms.
If difficulty concentrating is new, persistent or affecting your daily life, it is worth considering whether an underlying factor may be contributing.
What causes brain fog and poor concentration?
There is no single cause of brain fog. Concentration depends on several interconnected processes, including sleep, mood, nutrition, hormone regulation and general health.
The following are some of the possible causes that may be worth investigating.
1. Vitamin B12 deficiency
Vitamin B12 is essential for normal nerve function and the production of healthy red blood cells. Low levels can contribute to fatigue, difficulty concentrating and neurological symptoms.
Other possible symptoms include pins and needles, numbness, balance difficulties and changes in mood.
Vitamin B12 deficiency can develop due to inadequate dietary intake, problems absorbing the vitamin, certain gastrointestinal conditions or some medications.
Which blood test may help?
A vitamin B12 blood test measures the amount of B12 in your blood. If the result is borderline or does not fit your symptoms, a healthcare professional may recommend further assessment, such as methylmalonic acid testing, where appropriate.
2. Low folate levels
Folate, also known as vitamin B9, is important for DNA production and the formation of healthy red blood cells. Low folate can contribute to anaemia and fatigue, which may make it harder to concentrate.
Folate deficiency may be associated with a restricted diet, increased nutritional requirements or problems absorbing nutrients.
Which blood test may help?
A serum folate test measures folate in the blood. It is often assessed alongside vitamin B12 and a full blood count when investigating possible nutritional deficiencies.
3. Iron deficiency and low ferritin
Iron helps your body produce haemoglobin, the protein in red blood cells that carries oxygen around the body.
When iron stores are low, you may experience tiredness, weakness, reduced exercise tolerance and difficulty concentrating. Importantly, iron deficiency can occur before anaemia develops.
Ferritin is a protein that reflects your body’s iron stores, although it can also rise during inflammation or illness.
Which blood tests may help?
Ferritin: helps assess iron stores.
Iron studies: may include serum iron, transferrin or total iron-binding capacity, and transferrin saturation.
Full blood count (FBC): checks haemoglobin and other blood cell measurements and can help identify anaemia.
A normal haemoglobin result does not always rule out iron deficiency, so ferritin may be useful when symptoms and risk factors suggest depleted iron stores.
4. Thyroid problems
Your thyroid gland produces hormones that help regulate metabolism, energy levels and many other body functions.
An underactive thyroid, known as hypothyroidism, may cause fatigue, sluggishness, low mood and difficulty concentrating. An overactive thyroid, known as hyperthyroidism, can also affect focus and sleep and may cause anxiety, irritability or restlessness.
Because thyroid symptoms can overlap with many other conditions, blood testing can be helpful when thyroid dysfunction is suspected.
Which blood tests may help?
TSH: thyroid-stimulating hormone, commonly used as an initial thyroid function test.
Free T4 (FT4): measures circulating free thyroxine.
Free T3 (FT3): may be useful in selected circumstances, particularly when an overactive thyroid is suspected.
Thyroid antibodies: may be requested when an autoimmune thyroid condition is suspected.
The appropriate tests depend on symptoms, medical history and initial results. Not everyone needs a full thyroid panel or antibody testing.
5. Vitamin D deficiency
Vitamin D is important for bone health, muscle function and normal immune function. Low vitamin D may occur alongside fatigue and other symptoms, although brain fog alone cannot establish that vitamin D levels are low.
Testing may be useful where there are risk factors for deficiency, such as limited sun exposure, certain dietary patterns or conditions affecting absorption.
Which blood test may help?
The usual test for assessing vitamin D status is 25-hydroxyvitamin D (25-OH vitamin D). This is the standard blood test used to assess vitamin D levels.
6. Blood glucose problems
Glucose is one of the body’s main sources of energy. Problems with blood glucose regulation, including diabetes, can sometimes contribute to fatigue and difficulty concentrating.
Low blood glucose can cause shakiness, sweating, dizziness and confusion. High blood glucose may be associated with increased thirst, frequent urination and fatigue.
Brain fog alone does not mean that you have a blood sugar problem, but testing may be appropriate depending on your symptoms and risk factors.
Which blood tests may help?
HbA1c: provides an indication of average blood glucose levels over approximately the previous two to three months.
Fasting glucose: measures blood glucose after a period without eating.
Other glucose testing: may be recommended by a healthcare professional when further investigation is appropriate.
Insulin testing may be useful in selected clinical situations, but fasting insulin is not routinely required for everyone experiencing poor concentration.
7. Anaemia and other blood abnormalities
Anaemia occurs when haemoglobin levels are below the expected range. It can cause tiredness, weakness, dizziness, breathlessness and reduced concentration.
Iron deficiency is one possible cause, but anaemia can also be associated with vitamin B12 or folate deficiency, chronic disease, blood loss and other conditions.
Which blood test may help?
A full blood count (FBC) measures haemoglobin, red blood cells, white blood cells and platelets. It can help identify anaemia and other blood cell abnormalities that may need further investigation.
Additional tests depend on the pattern of results and the person’s symptoms.
8. Hormonal changes, including perimenopause and menopause
Hormonal changes can affect sleep, mood and energy levels, which may in turn influence concentration and focus.
Some women notice increased mental fatigue or difficulty staying focused during perimenopause and menopause. However, these symptoms can also have other explanations, including stress, poor sleep, iron deficiency and thyroid disorders.
Which blood tests may help?
Depending on symptoms, age and medical history, a healthcare professional may consider:
Thyroid function tests.
FBC and ferritin.
Vitamin B12 and folate.
Other investigations guided by symptoms.
Hormone blood tests, such as FSH or oestradiol, are not routinely necessary to diagnose perimenopause in otherwise healthy women aged 45 or over with typical symptoms. Testing may be appropriate in selected circumstances, including some people with symptoms at a younger age.
9. Poor sleep, stress and burnout
Sleep is essential for attention, learning and mental performance. When sleep is consistently disrupted, it can become harder to concentrate, process information and complete everyday tasks.
Stress and anxiety can also affect focus. When your attention is occupied by worries or ongoing demands, you may find it difficult to stay on task or think clearly.
These causes do not necessarily produce abnormal blood test results. A normal blood test does not mean your symptoms are not real or that there is nothing you can do to improve them.
If you regularly snore heavily, wake up gasping or feel excessively sleepy during the day, speak to your healthcare professional about possible sleep disorders, including sleep apnoea.
10. Medication, alcohol and other health conditions
Certain prescription medicines, over-the-counter products and substances can affect alertness, attention and concentration. Alcohol, recent infections and some chronic illnesses can also contribute.
Some people experience persistent brain fog after an infection, including COVID-19.
If your symptoms begin after starting a new medication or changing a dose, discuss this with your prescriber. Do not stop prescribed medication without appropriate advice.
Which blood tests are best for brain fog and poor concentration?
There is no single blood test that can diagnose brain fog. The most useful tests depend on your symptoms, medical history, diet, medications and other risk factors.
For someone experiencing persistent brain fog alongside fatigue or poor concentration, a healthcare professional may consider the following investigations.
| Blood test | What it can help investigate |
|---|---|
| Full blood count (FBC) | Anaemia and other blood cell abnormalities |
| Ferritin | Iron stores and possible iron deficiency |
| Iron studies | Further assessment of iron status |
| Vitamin B12 | Vitamin B12 deficiency |
| Folate (vitamin B9) | Folate deficiency |
| Thyroid function (TSH and, where appropriate, FT4) | Underactive or overactive thyroid |
| Vitamin D (25-OH vitamin D) | Vitamin D status |
| HbA1c | Average blood glucose and possible diabetes |
| Fasting glucose | Blood glucose at the time of testing |
| Kidney and liver function tests | Certain metabolic or organ-related abnormalities, where indicated |
How can you improve concentration and mental clarity naturally?
The best approach depends on the cause. A few practical habits may support concentration and general wellbeing while you investigate persistent symptoms.
Prioritise sleep. Maintain a consistent sleep schedule and allow enough time for rest. Seek advice if you regularly wake unrefreshed or feel excessively sleepy during the day.
Eat a balanced diet. Include a variety of foods containing protein, vegetables, fruit, whole grains and sources of essential vitamins and minerals, according to your individual dietary needs.
Stay hydrated. Dehydration can contribute to tiredness and difficulty concentrating.
Move regularly. Appropriate physical activity can support general health, mood and sleep.
Manage stress. Break demanding tasks into smaller steps, take regular breaks and make time for activities that help you unwind.
Reduce distractions. Try focusing on one task at a time, switching off unnecessary notifications and taking short breaks between periods of concentrated work.
Review alcohol and medication. Alcohol and certain medicines can affect sleep, alertness and concentration. Discuss concerns about medication with your healthcare professional.
Avoid taking supplements without a clear reason. More is not always better. Excessive intake of some vitamins and minerals can be harmful, and supplements may interact with medicines. If a deficiency is identified, seek advice on the appropriate treatment and follow-up.
These measures may help, but they should not replace medical assessment when symptoms are persistent, unexplained or worsening.
When should you seek medical advice?
Make an appointment with your GP if brain fog or poor concentration persists, keeps returning, is getting worse or interferes with work, relationships or everyday activities.
Seek urgent medical attention if you develop sudden confusion, difficulty speaking, facial drooping, weakness or numbness on one side, sudden loss of vision, or a sudden severe headache. These symptoms may indicate a medical emergency.
Do not assume that new or worsening concentration problems are simply due to stress, age or a vitamin deficiency.
Brain fog blood tests at Mybloods
If you are experiencing brain fog, poor concentration or unexplained mental fatigue, blood testing may provide useful information about your health.
At Mybloods, we offer private blood testing to help you access information about a range of health markers.
Our team can help you understand the available testing options. Your results should be considered alongside your symptoms and medical history, and abnormal or concerning findings should be discussed with an appropriate healthcare professional.
Take the first step towards understanding your health.
Visit Mybloods to explore our blood testing options or contact us to discuss which tests may be suitable for you.
Mybloods provides blood testing services and health information. This article is for educational purposes only and is not a substitute for medical advice, diagnosis or treatment.
Frequently asked questions about brain fog and concentration
1. What is the best blood test for brain fog?
There is no single best test. Depending on your symptoms and risk factors, useful investigations may include an FBC, ferritin, vitamin B12, folate, thyroid function and HbA1c or glucose testing.
2. Can low vitamin B12 cause poor concentration?
Yes. Vitamin B12 deficiency can contribute to fatigue, difficulty concentrating and neurological symptoms. A blood test can help assess B12 status, although some results may require further investigation.
3. Can low iron affect concentration?
Iron deficiency can contribute to tiredness, weakness and reduced concentration, even before anaemia develops. Ferritin is commonly used to assess iron stores, with additional iron studies or tests added when appropriate.
4. Can thyroid problems cause brain fog?
Both an underactive and an overactive thyroid can affect concentration, sleep, mood and mental clarity. Thyroid function testing can help identify thyroid abnormalities.
5. Can vitamin D deficiency cause brain fog?
Low vitamin D may occur alongside fatigue and other symptoms, but it is not possible to conclude that it is the cause of brain fog based on symptoms alone. A 25-OH vitamin D test can assess vitamin D status when testing is appropriate.
6. Can stress cause poor concentration?
Yes. Stress and anxiety can make it difficult to focus, process information and complete tasks. If symptoms persist or significantly affect your daily life, consider discussing them with your healthcare professional.
7. Why do I have brain fog if my blood tests are normal?
Brain fog can be associated with poor sleep, stress, anxiety, depression, medication effects, hormonal changes and other conditions that may not be detected by routine blood tests. If symptoms continue, speak to your GP about further assessment.
8. Should I take vitamins to improve concentration?
It is best to identify whether a deficiency or another issue is present before starting high-dose supplements. The appropriate treatment depends on the cause, and some supplements can be harmful in excessive amounts.
9. When should I get blood tests for brain fog?
Consider discussing testing with a healthcare professional if symptoms persist, recur or occur alongside unexplained fatigue or other symptoms. Seek medical advice promptly for worsening symptoms and urgent care for sudden neurological symptoms.
10. Can a blood test explain why I cannot focus?
It can sometimes identify a contributing factor, such as anaemia, vitamin deficiency, thyroid dysfunction or diabetes. However, blood tests are only one part of assessing concentration difficulties.