Forgetful, Foggy, and Frustrated?

Why Brain Fog Happens (and What Actually Helps)

Brain fog is one of those symptoms that can be hard to explain until you have lived it.

It might feel like walking through the day with a layer of cotton wool around your brain.

You forget words. You reread the same paragraph three times. You walk into a room and forget why you are there. Work takes longer. Simple decisions feel harder. Conversations take more effort.

You may not feel “unwell” in the traditional sense, but you know you are not simply not functioning like yourself.

Brain fog is not a formal diagnosis.

It is a symptom pattern.

It usually describes changes in memory, concentration, word-finding, mental clarity, processing speed, motivation, and mental stamina.

It can happen for a number of reasons – after poor sleep, during stress, around hormone changes, after viral illness, with nutrient deficiencies, with thyroid problems, with blood sugar instability, and in many chronic inflammatory or metabolic conditions.

The most important thing to know is this: brain fog is not laziness, lack of discipline, or “just getting older.”

It is often a sign that the brain is under strain. Your body is sending you signals.

And because the brain is highly sensitive to sleep, oxygen, glucose, hormones, inflammation, nutrients, stress chemistry, and blood flow, the most helpful approach is usually not to reach straight for a supplement.

It is to ask: what is making your brain work harder than it should?

What does brain fog actually feel like?

Brain fog can show up differently for different people, but common symptoms include:

– difficulty concentrating
– forgetfulness
– slower thinking
– losing your train of thought
– word-finding problems
– mental fatigue
– feeling easily overwhelmed
– trouble planning or prioritising
– reduced motivation
– feeling “flat” or mentally disconnected

Cleveland Clinic describes brain fog as a symptom cluster that may include difficulty focusing, confusion, fatigue, forgetfulness, losing your train of thought, mental exhaustion, slow thought processes, and trouble paying attention [1].

For some people, it is mild and short-lived after a bad night’s sleep.

For others, it becomes persistent and begins affecting work, parenting, relationships, confidence, and quality of life. It can have a huge impact on day to day life in some people, and make it hard to get through even basic tasks.

Some people may experience brain fog to the degree that they worry it’s the start of dementia, or something more serious…

Why brain fog happens

Your brain is metabolically demanding.

Although it only makes up a small proportion of body weight, it uses a large amount of your body’s energy each day.

For your brain to function well, it relies on stable blood sugar, oxygen delivery, healthy blood vessels, sleep-dependent repair, adequate nutrients, balanced hormones, and good communication between brain networks.

Brain fog can develop when one or more of these systems becomes disrupted.

It may be driven by:

– sleep loss or poor sleep quality
– chronic stress and nervous system overload
– low iron, B12, folate, vitamin D, or inadequate protein
– thyroid dysfunction
– perimenopause or menopause
– depression, anxiety, burnout, ADHD, or trauma load
– blood sugar instability, insulin resistance, diabetes, or reactive hypoglycaemia
– post-viral syndromes, including long COVID
– chronic inflammation or autoimmune disease
– medication side effects
– alcohol, cannabis, sedating medications, or anticholinergic medications.
– sleep apnoea or other sleep disorders
– migraine, concussion, neurological illness, or dementia-spectrum conditions

Often, brain fog is not caused by one single thing.

It is the result of several “small” pressures adding up: not enough sleep, heavier periods, low ferritin, high stress, blood sugar swings, perimenopause, less movement, and more mental load.

That is why a lifestyle medicine approach can be so effective: it looks at the whole system, to understand the root causes, and address brain fog at its core.

The sleep-brain fog connection

Poor sleep is one of the most common and under-recognised causes of brain fog, and what we often focus on first in our clinic.

Sleep is not just rest. It is literally what holds everything else together

Sleep is an active repair state for the brain.

During deeper stages of sleep, the brain consolidates memory, regulates emotion, clears metabolic waste, resets neurotransmitter systems, and restores the ability to focus the next day.

Research on the glymphatic system suggests that sleep supports the clearance of brain metabolites, including proteins such as amyloid-β and tau that are relevant to neurodegenerative disease pathways (ie preventing dementia and other neurodegenerative disease) [2].

Slow-wave sleep appears particularly important for this cleaning and restoration process.

Even without thinking about long-term brain health, most people know what one or two poor nights can do: slower processing, irritability, sugar cravings, low motivation, and reduced ability to cope.

But when sleep disruption becomes chronic, brain fog can become the new normal.

Sleep apnoea is especially important to consider when looking at brain fog, as it’s often missed, but can have huge impacts.

Obstructive sleep apnoea can cause repeated drops in oxygen and fragmented sleep, even when someone thinks they have slept for enough hours.

A review of cognitive deficits in adults with obstructive sleep apnoea found it caused significant impairments in working memory, attention, and executive function [3].

It’s worth thinking about sleep apnoea screening if brain fog comes with snoring, waking unrefreshed, morning headaches, dry mouth, high blood pressure, restless sleep, waking gasping, or significant daytime sleepiness.

A simple sleep study (either at home, or in a sleep clinic) can test for sleep apnoea, and help to guide what’s needed for management.

If you’re unsure whether to go down this pathway, talk to your health provider, or complete an initial screening test such as this one, to help determine your risk.

Sleep quality matters just as much as sleep quantity

Many people assume that if they are spending seven to eight hours in bed, their sleep must be adequate.

However, your brain cares about sleep quality and sleep architecture, not just the number of hours slept.

Sleep occurs in repeating cycles that include light sleep, deep (slow-wave) sleep, and REM (rapid eye movement) sleep.

Each stage appears to play a different role in cognitive function.

Deep sleep is particularly important for physical restoration, memory consolidation, and the brain’s waste-clearance systems, while REM sleep is involved in emotional processing, learning, creativity, and memory integration.

When sleep architecture becomes disrupted, people may wake feeling unrefreshed despite apparently getting enough sleep.

Common causes include sleep apnoea, frequent awakenings, chronic stress, alcohol use, chronic pain, restless legs syndrome, perimenopausal night sweats, medications, and irregular sleep schedules.

Research suggests that reductions in slow-wave sleep and fragmented sleep are associated with poorer attention, memory, executive function, and daytime cognitive performance [4]

In other words, you may be spending enough time asleep but not getting enough of the restorative stages of sleep that help the brain function optimally the next day.

Clues that sleep quality may be contributing to brain fog include:

• waking unrefreshed despite adequate sleep duration
• needing multiple alarms to wake up
• morning headaches
• excessive daytime sleepiness
• frequent overnight awakenings
• snoring or witnessed breathing pauses
• restless or fragmented sleep
• vivid dreams with non-restorative sleep
• worsening concentration after poor sleep
• relying heavily on caffeine to function

If sleep quality is in question, useful assessments may include:

• a sleep diary tracking sleep duration, awakenings, and daytime symptoms
• validated questionnaires such as the Epworth Sleepiness Scale or STOP-Bang questionnaire
• wearable sleep trackers, which may help identify patterns but should not be considered diagnostic
• home sleep apnoea testing for those at risk of obstructive sleep apnoea
• formal overnight polysomnography (sleep study) when more detailed assessment of sleep architecture or other sleep disorders is required

For many people with persistent brain fog, improving sleep quality can produce some of the most noticeable improvements in concentration, memory, mental clarity, and daytime energy.

Stress, burnout, and nervous system overload

Brain fog is incredibly common in burnout.

This is not because people are weak.

It is because prolonged stress changes how the brain allocates energy and attention.

When the nervous system is constantly scanning for threat, juggling responsibility, or running in high-output mode, the prefrontal cortex — the part of the brain involved in planning, working memory, impulse control, and decision-making — can become less efficient.

The brain shifts toward survival mode rather than reflective thinking.

This is why people under chronic stress often say:

“I can do the urgent things, but I can’t think clearly.”
“I’m functioning, but I’m not really present.”
“I can’t make simple decisions anymore.”
“I start things but don’t finish them.”
“I feel like my brain is full.”

Brain fog in this setting often improves when the nervous system is given more regular cues of safety: sleep, daylight, movement, stable meals, connection, breathing space, boundaries, and less cognitive overload.

Beating burnout related brain fog doesn’t come with quick fixes; instead it’s about helping your nervous system return to a place of balance.

Nutrient deficiencies: common, checkable, and often missed

The brain needs many nutrients to make neurotransmitters, maintain myelin, produce energy, regulate inflammation, and support oxygen delivery.

Several key nutrient issues can contribute to brain fog.

Iron

Iron is essential for oxygen transport, mitochondrial energy production, dopamine pathways, thyroid function, and healthy brain function.

But you do not need to be anaemic to feel the effects of low iron stores.

Iron deficiency is particularly common in menstruating women, people with heavy periods, vegetarians, pregnancy/postpartum, endurance athletes, people with gut issues, and those with low dietary iron intake.

A review of iron deficiency in women found that studies showed poorer cognition, worse mental health scores, and increased fatigue in women with iron deficiency at baseline [5].

Symptoms of low iron can include fatigue, poor concentration, low mood, restless legs, hair shedding, dizziness, shortness of breath on exertion, and cold intolerance.

It’s also important to know your numbers.

Ferritin is a marker of stored iron, so a “normal” haemoglobin does not rule out low iron stores.

And while there is no universally accepted optimal ferritin level for brain health, some research suggests that cognitive and fatigue-related symptoms can occur in iron deficiency well before anaemia develops [6]

Many clinicians (including us!) view ferritin levels below 30 µg/L to be deficient and will trial increasing ferritin levels to above 50 µg/L to treat symptoms such as fatigue, poor concentration, and brain fog [7]. Interestingly restless legs can often improve with a higher ferritin level (guidelines suggest aiming for 75µg/L), which also impacts on sleep.

The bottom line – if brain fog is accompanied by fatigue, hair loss, heavy periods, restless legs, or exercise intolerance, ferritin and iron studies are worth checking, and correcting if low.

Vitamin B12

When people think about nutrients linked with brain fog, vitamin B12 is often one of the first that comes to mind — and for good reason.

Vitamin B12 plays an essential role in nerve health, myelin production (the protective coating around nerves), red blood cell formation, DNA synthesis, and methylation pathways. These processes are fundamental for healthy brain communication, energy production, and cognitive function.

When B12 levels are low, the effects are not limited to tiredness.

Deficiency can contribute to a range of neurological and psychological symptoms, including brain fog, poor concentration, memory difficulties, low mood, numbness, tingling, balance problems, and fatigue [8].

What level of vitamin B12 is ideal for brain health?

Vitamin B12 deficiency is traditionally diagnosed when blood levels fall below the laboratory reference range. Most laboratories consider levels below approximately 150 pmol/L to be deficient, levels between 150–250 pmol/L to be borderline, and levels above 250 pmol/L to generally be adequate [9].

However, vitamin B12 and brain health is not always that simple.

Neurological symptoms can sometimes develop before levels fall into the clearly deficient range, and some people experience symptoms despite having a B12 result that appears “normal” on a standard blood test [10].

This is because serum B12 measures the amount of B12 circulating in the blood, but does not always tell us how effectively B12 is being used inside the cells.

Research has reported neurological symptoms occurring in people with B12 levels in the 150–300 pmol/L range, suggesting that a result within the laboratory reference range does not always rule out functional B12 insufficiency.

For this reason, clinicians may look more closely at B12 levels when someone has symptoms such as persistent brain fog, fatigue, memory changes, poor concentration, low mood, numbness, or tingling — particularly when B12 levels are below approximately 300 pmol/L.

Additional markers, such as methylmalonic acid (MMA) and homocysteine, can sometimes provide further information when B12 deficiency is suspected but the blood level is unclear [11

There is no universally accepted “optimal” B12 level specifically for cognitive function.

However, in practice, many clinicians aim for levels above 300 pmol/L in people with symptoms, with levels around 400–600 pmol/L often considered healthy from a functional perspective [12]. This is also the range we commonly aim for in our clinics.

The goal is not to achieve extremely high B12 levels, but to ensure the body has enough available B12 to support healthy neurological function, methylation pathways, and energy metabolism.

It is also important to remember that vitamin B12 is not a universal “brain fog cure.”

Supplementation is most likely to help when deficiency or borderline deficiency is present.

If B12 levels are already adequate, taking more is unlikely to dramatically improve cognition.

This is why testing and looking at the whole picture — including diet, symptoms, other nutrients, thyroid function, sleep, hormones, and metabolic health — is so important.

The link between vitamin B12, folate, and homocysteine

Vitamin B12 does not work in isolation. It works closely with folate (vitamin B9) and vitamin B6 in the body’s methylation pathways and in the breakdown of homocysteine.

When B12 or folate status is inadequate, homocysteine levels may rise. This is one reason that assessing folate alongside B12 can provide a more complete picture of nutritional status and brain health.

Folate

When we talk about nutrients for brain health, vitamin B12 often gets the spotlight — but folate (vitamin B9) is equally important.

Folate is involved in some of the brain’s most fundamental processes, including DNA repair, neurotransmitter production, and methylation — the chemical process that helps regulate gene expression, brain signalling, and the production and breakdown of important compounds in the body.

It also works closely with vitamin B12 to keep homocysteine levels in a healthy range [11].

When folate levels are low, the effects can extend beyond tiredness.

Folate deficiency has been associated with low mood, reduced concentration, memory difficulties, and impaired cognitive function. These symptoms can overlap with what many people describe as “brain fog” — feeling mentally slower, struggling to find words, or not feeling as sharp as usual [13].

However, folate testing is not always straightforward.

Serum folate levels can change depending on recent food intake, so a single result may not always reflect longer-term status.

In some situations, red blood cell (RBC) folate — which provides a longer-term picture of folate stores — may be considered.

The connection between folate, B12, and homocysteine

One of the most important reasons folate matters for brain health is its relationship with homocysteine.

Homocysteine is a naturally occurring amino acid that the body normally recycles using folate, vitamin B12, and vitamin B6. When these nutrients are insufficient, homocysteine can accumulate.

Higher homocysteine levels have been associated with poorer cognitive performance, increased brain atrophy, and a higher risk of cognitive decline and dementia [11].

This does not mean that homocysteine itself causes dementia, but it may act as a marker that important nutritional and metabolic pathways are not functioning optimally.

For people experiencing persistent brain fog — particularly alongside fatigue, low mood, memory changes, a vegetarian or vegan diet, digestive issues, or low B12 levels — checking folate alongside vitamin B12 and homocysteine can provide a more complete picture.

Similar to B12, there is no proven “perfect” folate level for brain function. The aim is not to push folate levels as high as possible, but to ensure the body has enough to support healthy methylation, nervous system function, and homocysteine metabolism.

The best foundation remains a folate-rich diet, including:

• leafy green vegetables (spinach, kale, rocket)
• legumes such as lentils, chickpeas, and beans
• asparagus and broccoli
• avocado
• nuts and seeds
• whole grains

For most people, food provides the ideal form and combination of nutrients needed to support long-term brain health.

When deficiency is present though, targeted supplementation may be helpful and should be guided by individual needs.

Vitamin D

Vitamin D is often associated with strong bones, but its role in the body goes much further.

Vitamin D receptors are found throughout the brain, and vitamin D is involved in immune regulation, inflammation, neurotransmitter function, muscle health, and overall wellbeing [14].

Low vitamin D levels can contribute to symptoms that overlap with brain fog, including fatigue, low mood, muscle aches, reduced energy, and feeling generally “not quite yourself”.

Observational studies have also found associations between lower vitamin D status and poorer cognitive function, although this does not necessarily mean that low vitamin D directly causes cognitive decline [15].

The bottom line is that the relationship between vitamin D and brain fog is likely to be indirect for many people.

Low vitamin D can affect sleep, mood, inflammation, immune function, and physical energy — all of which can influence how clearly we think and how well we function day to day.

What vitamin D level should we aim for?

Vitamin D status is measured using a blood test called 25-hydroxyvitamin D [25(OH)D].

While target ranges vary slightly between laboratories, a general guide is:

• <25 nmol/L – deficient
• 25–50 nmol/L – insufficient
• >50 nmol/L – generally considered adequate for most people

Many clinicians aiming for preventative health often consider levels around 75–100 nmol/L a reasonable target, particularly in people with ongoing symptoms, autoimmune conditions, low sun exposure, or recurrent infections.

However, there is no strong evidence that pushing vitamin D levels much higher improves brain function in people who are already sufficient – plus since the body stores vit D, it is toxic in high doses, so more is not always better!

When is it worth checking vitamin D?

Vitamin D testing is worth considering if brain fog occurs alongside:

• persistent fatigue
• low mood or seasonal changes in mood
• muscle aches or weakness
• bone or joint discomfort
• limited sun exposure
• darker skin pigmentation
• digestive conditions affecting absorption
• autoimmune or inflammatory conditions

Can vitamin D supplements fix brain fog?

This is where the evidence needs some nuance.

If someone is vitamin D deficient, correcting that deficiency may improve symptoms such as fatigue, muscle discomfort, and low mood.

However, routine vitamin D supplementation has not consistently been shown to improve cognition or brain fog in people who already have adequate vitamin D levels [16].

The goal is not to achieve the highest possible vitamin D level — it is to make sure your body has enough to function well – and this is why we often test levels.

If brain fog is persistent, vitamin D is one piece of the puzzle, but it is rarely the whole story.

Sleep quality, iron status, vitamin B12, folate, thyroid function, hormones, blood sugar regulation, stress, and lifestyle factors often need to be considered too.

Are you eating enough to fuel your brain?

Sometimes brain fog isn’t caused by a deficiency, hormone imbalance, or medical condition. Sometimes the brain simply isn’t getting enough fuel.

This is surprisingly common, particularly in busy people who skip breakfast, run on coffee, eat very little during the day, or are trying to lose weight while juggling work, family, and a long to-do list.

Although the brain makes up only around 2% of body weight, it uses approximately 20% of the body’s energy. It needs a steady supply of nutrients to support concentration, memory, decision-making, and mental stamina.

When meals are low in protein, fibre, and healthy fats — or when there are long gaps between meals — blood sugar levels can become more unstable. This may show up as:

• mid-afternoon energy crashes
• irritability or feeling “hangry”
• strong sugar cravings
• difficulty concentrating
• feeling shaky or anxious between meals
• needing caffeine to keep going
• feeling tired but wired later in the day

For many people, one of the simplest ways to improve mental clarity is to start the day with a protein-rich breakfast and build meals around protein, fibre, healthy fats, and minimally processed carbohydrates. It is not about eating perfectly — it is about giving the brain a more stable source of fuel.

Blood sugar, insulin resistance, and brain fog

If you’ve ever felt mentally foggy after a large sugary meal or struggled to think clearly when you’ve gone too long without eating, you’ve experienced how sensitive the brain can be to changes in blood sugar.

The brain relies heavily on glucose for energy, but it works best when glucose levels remain relatively stable. Both high and low blood sugar can affect concentration, memory, processing speed, mood, and mental performance.

A recent review examining glucose extremes and cognition found that high blood sugar levels were associated with reduced cognitive flexibility and slower mental processing, while low blood sugar impaired decision-making and critical thinking [17]. The CDC also notes that both high and low blood glucose levels can affect memory, learning, attention, and mood [18].

This doesn’t mean that everyone with brain fog has diabetes.

In fact, many people experiencing blood sugar-related brain fog have completely normal fasting glucose levels.

The issue is often more subtle and may involve insulin resistance, reactive hypoglycaemia, large glucose swings, or metabolic changes that develop during perimenopause and midlife.

Blood sugar may be worth exploring if brain fog occurs alongside:

• afternoon energy crashes
• sugar or carbohydrate cravings
• feeling shaky, irritable, or anxious between meals
• sleepiness after eating
• increased abdominal weight gain
• PCOS
• a history of gestational diabetes
• a strong family history of type 2 diabetes
• elevated triglycerides
• fatty liver
• perimenopause-related metabolic changes

Insulin resistance is particularly important because it can develop years before blood sugar levels become abnormal enough to meet the criteria for prediabetes or diabetes. During this time, people may notice changes in energy, appetite regulation, weight, and mental clarity.

Depending on your symptoms and risk factors, useful tests may include HbA1c, fasting glucose, fasting insulin, lipid studies, liver function tests, and sometimes a continuous glucose monitor (CGM) or oral glucose tolerance test.

The good news is that blood sugar regulation is often highly responsive to lifestyle changes. Improving protein and fibre intake, increasing physical activity, prioritising sleep, managing stress, and reducing highly processed foods can all help create a more stable metabolic environment for the brain.

As with many causes of brain fog, the goal is not perfect numbers. It is helping the brain access a steady, reliable source of energy so it can function at its best.

Could your thyroid be contributing to brain fog?

The thyroid is often one of the first things people think about when they experience persistent fatigue and brain fog — and for good reason.

Thyroid hormones influence almost every cell in the body. They help regulate energy production, metabolism, body temperature, mood, cholesterol levels, gut function, menstrual cycles, and brain function.

When thyroid hormone levels are too low (hypothyroidism), the brain can feel like it is running in slow motion. Common symptoms include fatigue, poor concentration, forgetfulness, low mood, slowed thinking, cold intolerance, constipation, dry skin, hair loss, weight gain, and heavy periods.

Interestingly, when researchers have asked people with hypothyroidism what “brain fog” actually feels like, many describe symptoms such as forgetfulness, difficulty concentrating, mental fatigue, sleepiness, and struggling to find the right words [19].

Another review described brain fog in hypothyroidism as a combination of fatigue, low mood, memory difficulties, reduced mental clarity, and word-finding problems [20].

The challenge is that thyroid symptoms are not unique to thyroid disease. Iron deficiency, poor sleep, burnout, perimenopause, depression, insulin resistance, and some medications can all produce very similar symptoms.

That is why testing is important.

Useful investigations may include:

• TSH (optimal range ~0.5–2.5 mIU/L)
• Free T4 (normal 12–18 pmol/L (with many women feeling best in the mid–upper range)
• Free T3 (normal 4.0–6.0 pmol/L, often optimal in the upper half of the range)
• Thyroid antibodies (TPO): to screen for autoimmune thyroid conditions such as Hashimoto’s, which become more common during midlife

It is also important to remember that thyroid results need interpretation in the context of the whole person. A mildly abnormal TSH does not always explain severe symptoms, and ongoing brain fog in someone already taking thyroid medication may have other contributing factors that also need addressing.

The hormone connection: perimenopause, menopause, and brain fog

If there is one group of people who frequently describe brain fog, it is women navigating perimenopause and menopause.

Many women describe feeling less sharp than they used to. They may lose words mid-sentence, struggle to multitask, forget appointments, walk into rooms and forget why they are there, or feel mentally overwhelmed by tasks that previously felt manageable.

For some, these changes can be unsettling enough to trigger fears about dementia.

The reassuring news is that cognitive symptoms are extremely common during the menopause transition. One review estimated that between 44% and 62% of women experience subjective cognitive difficulties during this stage of life [21].

Importantly, menopause-related brain fog is rarely caused by a simple lack of oestrogen alone.

Oestrogen has important effects on areas of the brain involved in memory, attention, sleep, mood, and energy regulation. However, during perimenopause, hormone levels often fluctuate dramatically rather than simply declining in a straight line. These fluctuations can affect sleep quality, mood, migraines, anxiety, hot flushes, and overall cognitive function [22].

Progesterone changes can also play a role. For some women, declining progesterone contributes to poorer sleep, increased anxiety, irritability, or feeling less emotionally resilient. Others find progesterone has a calming effect and notice symptoms when levels fluctuate.

In reality, many women are not experiencing brain fog because of hormones alone. They are experiencing a combination of hormonal changes, disrupted sleep, increased stress, night sweats, anxiety, caregiving responsibilities, work pressures, and the general demands of midlife.

If you are waking multiple times each night, lying awake at 3 am, experiencing hot flushes, and carrying a heavy mental load, it is hardly surprising that concentration and memory suffer the next day.

Does hormone therapy help brain fog?

This is one of the most common questions we hear in clinic, and it’s important to discuss what MHT helps with, vs what may be better addressed with diet and lifestyle.

Menopausal hormone therapy (MHT) is the most effective treatment for hot flushes and night sweats and can significantly improve quality of life for many women [23]. For women whose sleep is being disrupted by vasomotor symptoms, improving those symptoms may lead to better sleep and, in turn, better daytime concentration and mental clarity.

However, hormone therapy is not currently recommended specifically to prevent cognitive decline or dementia [23].

The evidence around menopause-related brain fog is also more nuanced.

While some women report improvements in concentration and mental clarity when menopausal symptoms are treated, there is currently insufficient evidence to recommend hormone therapy as a stand-alone treatment for cognitive symptoms – which is what we tend to see in our clinic.

Ideally, we also need to look at the bigger picture, including sleep, mood, cardiovascular health, metabolic health, exercise, nutrition, and other modifiable brain health factors [24].

The practical takeaway is simple:

• If brain fog occurs alongside hot flushes, night sweats, sleep disruption, mood changes, migraines, or cycle changes, hormones may be contributing.
• Treating menopausal symptoms can indirectly improve cognitive function by improving sleep and overall wellbeing.
• Hormone therapy should be individualised and considered as part of a broader treatment plan rather than a “brain health supplement.”

Long COVID and post-viral brain fog

Since the COVID-19 pandemic, brain fog has become a much more widely recognised symptom.

The CDC lists difficulty thinking or concentrating (“brain fog”) among the common symptoms of long COVID, alongside fatigue, headaches, sleep disturbance, dizziness, mood changes, altered smell or taste, and autonomic symptoms [25].

For some people, the brain fog that follows a viral illness can be profound. They may describe difficulty concentrating, slower thinking, memory lapses, mental exhaustion, or feeling as though their brain is operating through a haze.

Researchers believe several mechanisms may contribute, including persistent inflammation, immune dysregulation, autonomic nervous system dysfunction, vascular changes, mitochondrial stress, disrupted sleep, and mood-related factors [26].

One of the most important things to understand is that post-viral brain fog often behaves very differently from ordinary fatigue.

Many people find that pushing harder does not help and may actually make symptoms worse. This is particularly true for those experiencing post-exertional malaise (PEM), where physical or mental exertion can trigger a significant worsening of symptoms.

Management often requires a more strategic approach that may include:

• pacing and energy management
• sleep optimisation
• nutritional support and blood sugar stabilisation
• gradual rehabilitation
• autonomic nervous system support/mind body strategies
• reducing inflammation
• treatment of contributing medical conditions
• targeted medications and supplements as needed

Research into treatments is ongoing, although no single treatment has been proven to work for everyone [26].

Low-dose naltrexone (LDN), guanfacine with N-acetylcysteine (NAC), omega-3 fatty acids, creatine, and palmitoylethanolamide (PEA) show some early promise through their effects on neuroinflammation, brain energy metabolism, and cognitive function..

Correcting underlying deficiencies such as iron, vitamin B12, folate, and vitamin D may also help where present.

However, the foundations of treatment remain optimising sleep, managing post-exertional malaise, addressing autonomic dysfunction, and supporting overall recovery.

For more details on strategies to help, please see our detailed blog posts here and here.

Medications and substances that can affect mental clarity

Sometimes the cause of brain fog is sitting quietly in the medicine cabinet.

Medication side effects are a surprisingly common and often overlooked contributor to fatigue, poor concentration, memory problems, and mental slowing.

Common culprits include:

• sedating antihistamines
• sleeping tablets and benzodiazepines
• opioid pain medications
• some anti-nausea medications
• some bladder medications
• certain antidepressants and antipsychotics
• anticonvulsants and nerve pain medications
• muscle relaxants
• alcohol
• cannabis
• high-dose melatonin and other sedating supplements

One group of medications deserves special mention: drugs with anticholinergic effects.

These medications can interfere with acetylcholine, a neurotransmitter involved in learning, memory, and attention. A clinical review found that higher anticholinergic burden was associated with cognitive impairment, delirium, and dementia risk, particularly in older adults, although younger people can also be affected [27].

This does not mean medications should be stopped suddenly or without medical advice. However, if brain fog developed after starting a new medication, increasing a dose, or adding a supplement, it is worth reviewing whether treatment may be contributing.

Sometimes the solution is not another supplement or another test — it is identifying something that is already affecting the brain’s ability to function at its best.

What should you check if brain fog isn’t improving?

If brain fog is persistent, worsening, or affecting your quality of life, it is worth taking a structured approach rather than simply trying random supplements.

The right assessment depends on your symptoms, age, medical history, medications, menstrual status, sleep, and lifestyle factors — but common areas to review include:

Sleep quality

Poor sleep is one of the most common and reversible contributors to brain fog.

Consider:

• Are you getting enough sleep?
• Do you wake feeling refreshed?
• Do you snore, wake with headaches, gasp during sleep, or feel excessively tired during the day?
• Are hot flushes, pain, restless legs, alcohol, or stress disrupting sleep?

Consider sleep apnoea screening if symptoms suggest it.

Nutrient status

Check for common deficiencies that can affect energy, concentration, and neurological function:

• Ferritin and iron studies
• Vitamin B12 (with methylmalonic acid or homocysteine if borderline)
• Folate
• Vitamin D

Consider other nutrients such as magnesium, zinc, iodine, and omega-3 intake depending on dietary pattern and symptoms.

Thyroid function

Thyroid dysfunction can mimic many symptoms of brain fog.

Consider:

• TSH
• Free T4
• Thyroid antibodies and/or free T3 when clinically indicated.

Metabolic health

Blood sugar instability and insulin resistance can contribute to fluctuating energy, poor concentration, and fatigue.

Useful markers may include:

• HbA1c
• Fasting glucose
• Fasting insulin (where appropriate)
• Lipids
• Liver enzymes
• Blood pressure and waist circumference

Hormones and midlife changes

For women in their 40s and 50s, consider whether perimenopause or menopause symptoms are contributing.

Assessment is usually based on:

• age
• symptoms
• menstrual changes
• sleep quality
• vasomotor symptoms (hot flushes/night sweats)

A single hormone test is often not helpful during perimenopause because levels fluctuate significantly.

Medications, supplements, and substances

Review anything that may be affecting cognition, including:

• sedating antihistamines
• sleeping tablets
• benzodiazepines
• some antidepressants or antipsychotics
• anticonvulsants
• alcohol or cannabis
• new supplements or dose changes

Medication review is particularly important if symptoms started after a new treatment was introduced.

Stress, mental health, and cognitive load

Consider the impact of:

• chronic stress
• burnout
• anxiety
• depression
• ADHD
• ongoing mental overload

A brain that is constantly managing stress and competing demands may struggle with attention, memory, and focus.

Post-viral symptoms

If symptoms started after COVID or another infection, consider Long COVID or post-viral syndromes, particularly if brain fog occurs alongside fatigue, sleep disturbance, dizziness, headaches, or post-exertional worsening.

Inflammatory or autoimmune conditions

Consider further assessment if brain fog occurs with symptoms such as:

• joint pain or swelling
• rashes
• gut symptoms
• unexplained weight changes
• fevers
• abnormal blood tests

When to seek urgent medical review

Most brain fog is gradual and not dangerous. However, seek urgent assessment for sudden or rapidly worsening cognitive symptoms, particularly if associated with:

• weakness or numbness on one side
• facial drooping
• difficulty speaking
• sudden severe headache
• seizures
• new confusion or disorientation
• vision loss
• loss of balance or coordination
• symptoms after a head injury

Sudden confusion or delirium should always be medically assessed rather than assumed to be ordinary brain fog [19].

The aim is not to find one “magic fix”. Brain fog is often the result of several small contributors adding up — and improving even a few of these areas can make a meaningful difference.

What helps brain fog?

The best treatment depends on why your brain feels foggy. There is no single “brain fog supplement” that fixes everything — because brain fog is usually a sign that one or more systems are under strain.

The most effective approach is to support the foundations that the brain relies on: sleep, stable energy, movement, nutrients, hormones, and recovery [29].

1. Build a brain-supportive breakfast

For many people, the first improvement is not a supplement — it is eating enough of the right foods.

A brain-supportive breakfast helps provide steady energy and reduces the blood sugar swings that can contribute to mid-morning fatigue, cravings, irritability, and the classic 3 pm crash.

Aim for:

• 25–35 g protein where possible
• fibre-rich carbohydrates
• healthy fats
• good hydration
• minimal added sugar

Examples include Greek yoghurt with berries, nuts and seeds; eggs with avocado and wholegrain toast; tofu scramble with vegetables; or a protein smoothie with berries, chia seeds, and nut butter.

The goal is not perfection. It is giving your brain a more reliable fuel supply.

2. Prioritise sleep quality

Sleep is one of the most powerful “brain fog treatments” available.

Start with the basics:

• keep a consistent wake time
• get morning daylight exposure
• avoid caffeine too late in the day
• reduce alcohol, especially close to bedtime
• create a wind-down routine
• keep your bedroom cool and dark
• address sleep disruptors such as hot flushes, pain, reflux, restless legs, or snoring

If insomnia is persistent, cognitive behavioural therapy for insomnia (CBT-I) has the strongest evidence base. If sleep apnoea is suspected, testing and treatment can make a significant difference.

For more detailed tips on sleep, see our blog post here.

For tips on sleep in peri/menopause, read this.

3. Move your body — but match the dose to your body

Exercise is one of the most consistently supported strategies for brain health.

Regular movement improves:

• blood flow to the brain
• insulin sensitivity
• mood
• sleep quality
• mitochondrial function
• neuroplasticity

For many people, a combination of resistance training, walking, aerobic exercise, and maintaining muscle mass is ideal.

However, more is not always better. If brain fog is related to Long COVID, chronic fatigue, or post-exertional malaise, pushing through can worsen symptoms. In these situations, pacing and gradual rehabilitation are often more appropriate.

4. Eat for long-term brain health

Brain health is influenced more by overall dietary patterns than individual “superfoods”.

Mediterranean, DASH, and MIND-style dietary patterns — rich in vegetables, leafy greens, berries, legumes, nuts, extra virgin olive oil, whole grains, and omega-3-rich foods — are associated with better cognitive outcomes and slower cognitive decline – especially when combined with exercise, brain challenges, social connection and reducing cardiovascular risk factors. [30]

The MIND diet combines elements of Mediterranean and DASH eating patterns and focuses on foods associated with brain health while limiting highly processed foods, excess sugar, and saturated fats.

The message is simple: the brain responds best to a combination of healthy habits rather than a single intervention.

5. Reduce cognitive overload

Sometimes brain fog is not because the brain is failing — it is because the brain is overloaded.

Useful strategies include:

• using lists and reminders rather than relying on memory
• reducing multitasking
• batching similar tasks together
• protecting uninterrupted focus time
• simplifying routines
• planning meals ahead
• creating recovery time after demanding days
• reducing unnecessary phone and notification overload

These strategies do not replace treating the underlying cause, but they reduce the mental load while your brain is recovering.

Supplements for brain fog: what is worth considering?

Supplements can be helpful in the right situation, but there is not one single ‘brain fog’ fix.

Supplementation works best when they address a specific need — such as correcting a deficiency, supporting sleep, or targeting a particular pathway.

Correct deficiencies first

The strongest evidence is for correcting genuine deficiencies:

Vitamin B12

• Important for nerve function, myelin, and methylation.
• Supplementation is helpful when deficiency or borderline deficiency is present.
• It is unlikely to dramatically improve cognition if B12 levels are already optimal.

Iron

• Low ferritin can contribute to fatigue, poor concentration, restless legs, and reduced cognitive function.
• Replace when deficiency is confirmed and investigate the cause of low iron.

Vitamin D

• Correct deficiency, particularly if there is low sunlight exposure, fatigue, low mood, or musculoskeletal symptoms.
• Vitamin D is not a proven stand-alone treatment for brain fog but supports overall health.

Supplements with emerging or supportive evidence

Omega-3 fatty acids (EPA/DHA)
Omega-3s support neuronal membranes and have anti-inflammatory effects. Higher omega-3 intake (1-2g/day) has been associated with lower risk of cognitive decline, particularly with DHA intake [31]. They may be most useful in people with low fish intake or increased cardiometabolic risk. Caution if on blood thinners or cardiac medications.

Creatine
Creatine supports cellular energy production in both muscle and the brain. Studies suggest it may improve memory and cognitive performance, particularly in older adults, during the menopausal transition, or in situations where brain energy demands are increased, such as sleep deprivation or high cognitive load. Typical dose is 3–5 g creatine monohydrate daily (avoid if kidney impairment). [32] [33].

Magnesium
Magnesium may be useful when brain fog is linked with poor sleep, stress, muscle tension, or migraines. Evidence is strongest for improving sleep and relaxation rather than directly treating brain fog. A 2024 trial found magnesium L-threonate improved aspects of sleep quality, mood, energy, and daytime functioning, although more research is needed; typical dose is 1-2g/day [34].

Lion’s mane mushroom
Early research suggests possible cognitive benefits, but studies are small and it is not yet considered a first-line treatment for brain fog [35].

Rhodiola rosea
May help fatigue and stress resilience. Evidence in Long COVID-related cognitive symptoms remains preliminary [36].

Ginkgo biloba
Some studies show benefits, particularly in Long COVID related brain fog, however there is no evidence currently to support routine use for preventing cognitive decline or treating brain fog. May interact with blood-thinning medications [36].

NAC, CoQ10, alpha-lipoic acid, and citicoline
These are interesting because of their roles in oxidative stress, mitochondrial function, and inflammation.

However, evidence for general brain fog remains limited. NAC has particular interest in Long COVID research, including in combination with guanfacine, but more clinical trials are needed [37].

Please always check with your health provider before trialling supplements, especially if you have any chronic health conditions, or take any prescription medications, as supplements can be unsafe in some circumstances, and may also interact with pharmaceutical treatments.

A brain fog action plan.

Brain fog is rarely solved by one magic intervention.

The most effective approach is usually layered:

1. Screen for, identify, and treat reversible causes.
2. Improve sleep quality.
3. Stabilise blood sugar with protein, fibre, and regular meals.
4. Correct nutrient deficiencies.
5. Support thyroid and hormone health where relevant.
6. Exercise in a way that matches your current capacity.
7. Reduce chronic stress and cognitive overload.
8. Use supplements strategically rather than randomly.

Your brain is constantly responding to the environment you give it — sleep, nutrition, movement, hormones, stress, and recovery all influence how clearly it can think.

Often, the biggest improvements come not from doing more, but from removing the things that are quietly draining your brain’s energy.

The bottom line

Brain fog is common, but it is not something you simply have to accept as part of getting older or being busy.

It is often your brain’s way of signalling that something needs attention — whether that is poor sleep, nutrient deficiencies, hormonal changes, blood sugar instability, chronic stress, inflammation, medication effects, or simply too much cognitive load.

The good news is that many of the factors that contribute to brain fog are modifiable. The goal is not to chase a quick fix or find one “brain-boosting” supplement, but to understand what your brain needs and address the underlying drivers.

For some people, the answer may be improving sleep. For others, it may be correcting iron or B12 deficiency, supporting thyroid or menopause symptoms, improving metabolic health, recovering from illness, reducing stress, or creating more space for rest and recovery.

Brain fog is not a sign that your brain is failing — it is a sign that your brain deserves support.

By taking a whole-person approach and focusing on the foundations of brain health, many people can regain the clarity, energy, and confidence they feel they have lost.

If you’d like to learn more about the topics we’ve covered in this article, please check out our courses page.

We also have many other resources in our articles, and in our free stuff section.

If you feel like you need additional help, we offer 1:1 consultations NZ wide.

You are also very welcome to share this article with your health provider to provide a framework to work through together, and to take a holistic approach to managing brain fog.

We hope you’ve found it helpful, and please do check out our other posts for evidence based lifestyle medicine topics!

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