Why Do I Have Brain Fog? – 5 Causes to Consider - Thorne Asia

Why Do I Have Brain Fog? – 5 Causes to Consider

Brain fog might sound more like a dangerous weather condition than a health concern, but it is actually a symptom that many people experience. Brain fog isn’t a medical term, and you won’t find an official definition for it. Brain fog has really been defined by the individuals who experience it and describe their symptoms to a health professional. Most commonly, the symptoms reported include:

  1. Mild forgetfulness
  2. A sense of thoughts being slowed, hard to form, and hard to process
  3. Poor task attention 
  4. A lack of mental clarity
  5. Feelings of detachment and tiredness
  6. General feeling that your head and thoughts are in a “fog”

Symptoms of brain fog can have many possible causes. The following are several of the most common causes – but there could be others.


1. Lack of sleep

Sleep has an impact on so many areas of health that it shouldn’t be a surprise to see it on this list. Studies show that sleep is important for maintaining the ways that neurons (the cells of the brain) communicate with each other.1

A landmark 2000 study found that moderate sleep deprivation of ~18 hours created brain and motor impairment equivalent to a blood alcohol level of 0.05 percent.2 Symptoms included fatigue, slowed reaction times, and decreased memory and recall.

Longer sleep deprivation (up to 48 hours) produced symptoms equivalent to a blood alcohol level of 0.1 percent – above the federal legal limit for driving!


2. Medications

Medications (over-the-counter and prescription) can be important causes of brain fog. Chemotherapy drugs are well-documented causes of brain fog. Sometimes called “chemo brain,” this form can linger long after chemotherapy is over and an individual has recovered. 

Medications that act directly on brain function, such as sleep aids, anti-anxiety meds, and some psychiatric drugs can induce brain fog. So can antihistamines, opiate pain medications, some drugs used for high blood pressure, and anti-seizure medications. If you are experiencing brain fog and taking a medication that can cause these symptoms, then discuss your concerns with the health professional who prescribed the medication for you.


3. An underlying health condition

There are some health conditions you might not connect to the symptoms of brain fog. Some of the most commonly reported conditions are multiple sclerosis, fibromyalgia3 (sometimes called fibro fog), and chronic fatigue syndrome.

Psychiatric conditions like bipolar disorder, depression, and anxiety are associated with brain fog. Other conditions linked to brain fog include sleep apnea, lupus, diabetes,4 migraine, and postural tachycardia syndrome (POTS). Finally, brain fog can be an early sign of more serious memory loss or brain impairment – or a symptom of a past brain injury, like a concussion.5 


4. A hormonal imbalance

Hormonal imbalances are well-recognized causes of brain fog.6 Low thyroid function often presents with symptoms of fatigue, forgetfulness, and low mood. Thyroid imbalance is relatively common, especially in women and older adults.

Menopause7 and andropause8 (“male menopause”) are normal life transitions that cause fluctuations in multiple hormones – and both can be causes of brain fog. In women, these symptoms are often associated with transitional levels of estrogen and progesterone, while they are more often tied to natural declines in testosterone in men.


5. Nutritional deficiency

Some nutrient deficiencies can lead to brain fog. Nutrients that can cause anemia when they are deficient have long been associated with symptoms of brain fog.9 These nutrients include vitamin 12, folic acid (folate), and iron. This could be related to low hemoglobin, which reduces delivery of oxygen to the brain by red blood cells.

Essential fatty acids, such as those found in fatty fish, fish oil, nuts, and seeds, are important for normal brain function, and low levels might contribute to diminished mental performance and low mood.10 Finally, low levels of magnesium and vitamin D11 are related to brain fog symptoms and cognitive function, especially in aging.

Most causes of brain fog can be managed when you identify them. Sleep can be improved, medications can be better managed to minimize side effects, and hormonal and nutritional challenges can be tested for and addressed.



  1. Nir Y, Andrillon T, Marmelshtein A, et al. Selective neuronal lapses precede human cognitive lapses following sleep deprivation. Nat Med 2017;23(12):1474-1480. 
  2. PubMed Central Link. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1739867/ [Accessed May 12, 2020.]
  3. Katz R, Heard A, Mills M, Leavitt F. The prevalence and clinical impact of reported cognitive difficulties (fibrofog) in patients with rheumatic disease with and without fibromyalgia. JCR J Clin Rheumatol 2004;10(2):53-58. 
  4. Cuevas H, Stuifbergen A, Brown S, Rock J. Thinking about cognitive function: perceptions of cognitive changes in people with type 2 diabetes. Diabetes Educ 2017;43(5):486-494. 
  5. Biagianti B, Stocchetti N, Brambilla P, Van Vleet T. Brain dysfunction underlying prolonged post-concussive syndrome: A systematic review. J Affect Disord 2020;262:71-76. 
  6. Samuels M. Psychiatric and cognitive manifestations of hypothyroidism. Curr Opin Endocrinol Diabetes Obes 2014;21(5):377-383. 
  7. Maki P, Henderson V. Cognition and the menopause transition. Menopause 2016;23(7):803-805. 
  8. Martin D, Wittert G, Burns N, et al. Testosterone and cognitive function in aging men: Data from the Florey Adelaide Male Ageing Study (FAMAS). Maturitas 2007;57(2):182-194. 
  9. Ranjan A, Jyothi Y, Das K, Mary A. Effects of anemia on cognitive function. J Pharm Res 2017;16(2):134-142.
  10. Chang C, Ke D, Chen J. Essential fatty acids and human brain. Acta Neurol Taiwanica 2009;18(4):231-241.
  11. Peeri N, Egan K, Tao M. Association of vitamin D and magnesium status with cognitive function in older adults: results from the National Health and Nutrition Examination Survey (NHANES) 2011 to 2014 (FS05-03-19). Curr Dev Nutr 2019;3(Supplement 1).
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