Key Takeaway: Brain fog is not a medical diagnosis -- it is a cluster of cognitive symptoms including difficulty concentrating, forgetfulness, and mental fatigue. The causes range from sleep deprivation and chronic stress to nutritional gaps that are rarely checked during routine bloodwork. Understanding which factor may apply to you, with the help of a healthcare professional, is the first step toward feeling like yourself again.
What is brain fog?
Brain fog is a term for a range of symptoms that affect your ability to think clearly. According to Cleveland Clinic, it can include trouble focusing, difficulty staying attentive, slow reaction times, frequent loss of train of thought, and cloudiness in judgment (Cleveland Clinic).
It is not a formal medical diagnosis. Rather, it is a signal that something in the body or lifestyle may be interfering with normal cognitive function -- and it is worth understanding what that something might be.
12 things commonly associated with brain fog
1. Poor sleep
Sleep deprivation is the most commonly cited driver of brain fog. During deep sleep, the brain clears metabolic waste through the glymphatic system. Chronic sleep restriction -- even losing 1-2 hours per night -- has been linked to changes in memory consolidation, attention, and processing speed.
2. Chronic stress
Prolonged stress elevates cortisol, which, over time, has been associated with changes in hippocampal function -- the brain region involved in memory and learning. Cleveland Clinic describes brain fog as "a sort of manifestation of some type of inflammation or chronic stress response" (Cleveland Clinic).
3. Iron deficiency
A systematic review found that iron deficiency -- even without anemia -- was associated with reduced cognitive performance in women, particularly attention and concentration. In iron-deficient women, iron supplementation was linked to faster completion of cognitive tasks (Murray-Kolb & Beard, J Nutr, 2007; PubMed).
4. Vitamin B12 deficiency
A systematic review of 43 studies discussed how B12 deficiency has been associated with cognitive impairment, including "mental fogginess" and difficulty with concentration (Langan & Goodbred, 2017; PubMed).
5. Vitamin D deficiency
Low vitamin D levels have been associated with cognitive symptoms in observational studies. Vitamin D receptors are present throughout the brain, including in regions involved in memory and executive function.
6. Copper deficiency
Copper is an essential trace mineral, and copper deficiency is a recognised nutritional condition. Copper contributes to the normal functioning of the nervous system, and it contributes to normal iron transport in the body. Because these are everyday roles of an essential nutrient, copper status is something a clinician may consider when reviewing nutritional gaps.
One reason copper deficiency can be overlooked is its connection to iron. Ceruloplasmin, a copper-carrying protein, is involved in iron metabolism: it helps convert iron from Fe2+ to Fe3+ so it can be carried by transferrin. This is one of the reasons copper contributes to normal iron transport in the body. When copper status is low, iron handling can be affected -- even when total body iron stores appear normal.
Copper deficiency is rarely checked in routine bloodwork, which is one reason it can be overlooked. A ceruloplasmin and serum copper test, ordered by your doctor, can help identify it. If you think your copper status may be low, speak with a healthcare professional.
7. Hormonal changes
Fluctuations in estrogen and progesterone -- during perimenopause, menopause, pregnancy, or menstrual cycles -- are commonly reported alongside brain fog.
8. Blood sugar instability
Rapid swings in blood glucose -- from skipping meals, high-sugar diets, or insulin resistance -- can temporarily affect cognitive function. The brain depends on a steady supply of glucose for energy.
9. Chronic inflammation
Neuroinflammation -- inflammation within the brain -- has been studied in relation to cognitive symptoms, including in the context of post-viral brain fog (such as post-COVID), autoimmune conditions, and chronic infections.
10. Sedentary lifestyle
Regular physical activity increases blood flow to the brain and is associated with the release of brain-derived neurotrophic factor (BDNF). Prolonged inactivity does the opposite.
11. Medication side effects
Several classes of medications are known to cause cognitive side effects, including antihistamines, benzodiazepines, proton pump inhibitors (PPIs), statins, and certain blood pressure medications. If brain fog started after a new medication, discuss it with your prescriber.
12. Gut health disruption
Emerging research examines the gut-brain axis -- the communication pathway between the intestinal microbiome and the brain. Dysbiosis (imbalanced gut bacteria) has been associated with neuroinflammation and cognitive symptoms in some studies.
Why copper is rarely tested
Unlike iron, B12, and vitamin D, copper is not part of standard blood panels. A doctor must specifically order:
- Serum copper
- Ceruloplasmin
Without these tests, copper status is easy to miss. A person can present with fatigue and even anemia and receive iron supplements that do not change things, because the underlying picture involves copper-mediated iron handling -- which is why some clinicians look at copper and iron together.
Copper deficiency can take months to years to diagnose (PMC10733163; PMC).
Who is at risk?
People more likely to have low copper levels include:
- Those who supplement zinc without copper (zinc competes for absorption)
- Post-bariatric surgery patients (~10% develop copper deficiency)
- People with celiac disease or Crohn's disease
- People on long-term PPI medications
- Those on highly restrictive diets
How to identify your cause
Brain fog is a symptom, not a root cause. The approach depends on identifying which factor is at play -- ideally alongside a healthcare professional:
Start with the basics: Are you sleeping 7-9 hours? Managing stress? Eating a varied diet? Exercising regularly? These account for the majority of cases.
Check your bloodwork: If lifestyle factors are addressed and brain fog persists, ask your doctor to test:
- Iron and ferritin
- Vitamin B12
- Vitamin D
- Serum copper and ceruloplasmin
- Thyroid function (TSH, T4)
- Blood glucose (fasting or HbA1c)
- Zinc (if you supplement zinc)
Review medications: Cross-check any medications you take against cognitive side effects with your prescriber.
Frequently asked questions
Is brain fog a real medical condition?
Brain fog is not a formal medical diagnosis. It is a term used to describe a cluster of cognitive symptoms. However, the symptoms are real and can significantly affect daily life. The key is identifying the underlying cause with the help of a healthcare professional.
Can nutritional deficiencies be associated with brain fog?
Deficiencies in iron, vitamin B12, vitamin D, and copper have all been associated with cognitive symptoms in published research. These are testable through your doctor and best addressed with medical guidance.
When should I see a doctor about brain fog?
If brain fog persists for more than a few weeks despite adequate sleep and stress management, or if it is accompanied by other symptoms (numbness, tremors, severe fatigue, unexplained weight changes), consult a healthcare provider.
What is copper's role in the body?
Copper is an essential trace mineral. Among its recognised roles, copper contributes to the normal functioning of the nervous system and to normal iron transport in the body. It is not a treatment for any symptom. If you suspect your copper status may be low, ask your doctor for a serum copper and ceruloplasmin test.
What is the best way to support clear thinking day to day?
There is no universal shortcut. Improving sleep quality, hydration, and physical activity are the foundations most people benefit from. For evidence-based strategies, see our guide on how to get rid of brain fog. If a specific nutritional gap is identified through bloodwork, addressing it under medical guidance is the appropriate path.
The copper connection
Among the 12 factors above, copper deficiency is one of the least commonly discussed -- yet copper is an essential nutrient with well-documented roles in the body. Copper contributes to the normal functioning of the nervous system. It also contributes to normal iron transport in the body and to the protection of cells from oxidative stress.
For those whose bloodwork reveals low copper or ceruloplasmin levels, the appropriate step is to address that nutritional gap together with a healthcare professional. Sodium copper chlorophyllin is a plant-derived form of bound copper used in supplements like CSR-01. A food supplement is meant to complement a varied diet, not to treat, cure, or prevent any condition.
This is about giving your body an essential nutrient it may be missing -- not a promise about symptoms. If you have wondered whether something in your nutrition is part of the picture, that is a conversation worth having with your doctor.
Important: Copper supplementation is not appropriate for individuals with Wilson's disease. Consult your healthcare provider before starting any copper supplement.
Sources:
- Cleveland Clinic. "Brain Fog: What It Is, Causes, Symptoms & Treatment." Link
- Cleveland Clinic. "Strategies for Busting Up Brain Fog." Link
- Murray-Kolb LE, Beard JL. (2007). "Iron treatment normalizes cognitive functioning in young women." Am J Clin Nutr. PubMed
- Langan RC, Goodbred AJ. (2017). "Vitamin B12 deficiency." Am Fam Physician. PubMed
- PMC6941745. "Copper and the brain noradrenergic system." PMC
- PMC9698384. "The role of copper homeostasis in brain disease." PMC
- PMC10733163. "Copper deficiency: an overlooked diagnosis." PMC
Wondering whether copper is part of your nutrition picture?
Take the Copper Nutrition Quiz to find out.
Related research
Continue exploring this topic:
Frequently asked questions
What are the most common causes of brain fog?
The usual contributors are poor sleep, chronic stress, dehydration, nutrient gaps (including minerals such as copper and iron), blood-sugar swings, and doing too much at once.
Can a mineral deficiency be associated with brain fog?
Deficiencies in copper, iron, B12 and magnesium have been associated with reduced focus and mental clarity in research, because the body relies on these nutrients for normal function.
How long does brain fog last?
It depends on the cause. Sleep- or stress-related fog can clear within days once addressed; fog linked to nutrient gaps may take a few weeks of consistent changes guided by a professional.
