Do Thyroid Disorders Cause Forgetfulness and Brain Fog?

The Effects of Hypothyroidism and Hyperthyroidism on Memory

How the Thyroid Can Affect Memory
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Feeling like you're forgetting things more often, or your brain is in a fog? There are many causes of memory loss, and while some are related to Alzheimer's disease or other dementias, others are due to potentially reversible causes, one of which is a thyroid disorder.

Does Your Thyroid Functioning Affect Your Memory?

The thyroid is a gland in your neck that produces hormones that regulate growth and development. But, if it's not functioning well, problems with the thyroid can cause many challenges including extreme fatigue, weight loss or gain, rapid heartbeat, and hair loss.

Interestingly, both hypothyroidism and hyperthyroidism can also cause cognitive problems that can mimic symptoms of mild dementia.

What Is Dementia?

Dementia is a blanket term which refers to a decrease in memory and other cognitive skills needed to perform routine activities of daily living.

The presentation of dementia varies from one person to another. Nevertheless, a person with dementia typically presents with at least two of the following symptoms:

Symptoms of mild dementia sometimes develop when thyroid levels are abnormal, but fortunately, they generally appear to resolve with treatment.

Cognitive Symptoms in Hypothyroidism

Hypothyroidism is a medical condition where not enough of the thyroid hormone is being produced.

Cognitive symptoms of people with hypothyroidism include memory problems and difficulty concentrating. Research has shown that verbal memory, in particular, may be affected by hypothyroidism. Another study found decreased hippocampal volume in adults with untreated hypothyroidism.

Small changes in executive functioning have also been noted in untreated or under-treated hypothyroidism. Executive functioning can include abilities such as planning, impulse control and making decisions. It's important to note, however, that larger changes in executive functioning are likely not related to hypothyroidism and thus should be reported to the physician.

Cognitive Symptoms in Hyperthyroidism

Hyperthyroidism is when too much of the thyroid hormone is produced.

Some people with hyperthyroidism (also called Graves disease) commonly exhibit poor concentration, slower reaction times, decreased spatial organization and decreased visual processing skills.

Are Thyroid Problems Associated with an Increased Dementia Risk?

Several researchers have questioned whether hyperthyroidism or hypothyroidism increases the risk for dementia to develop. Research on this question includes the following:

  • One study found that participants with subclinical hyperthyroidism (defined as TSH levels lower than 0.10 mIU/L) demonstrated a larger cognitive decline over the course of the research and an increased risk of dementia. There was not an increased risk in those with less significant TSH levels, nor was a risk correlated with subclinical hypothyroid levels.
  • A second study involved 1750 older adults in Mexico. The researchers found that overt hypothyroidism was the condition most strongly connected to reduced cognitive functioning.
  • Researchers also took a look at several studies on thyroid function and cognition. They concluded that subclinical hyperthyroidism could be correlated with a risk of dementia; however, they also found that mini-mental state exam (MMSE) scores did not decline any faster with the presence of hyperthyroidism, hypothyroidism or normal thyroid functioning.
  • Another review of 13 different studies found that subclinical hypothyroidism was only correlated with an increased dementia risk in those who were younger than 75 and in those who had higher TSH levels.
  • In a post-mortem study of older adults, hypothyroidism that was treated was not found to increase the risk of Alzheimer's brain pathology. This doesn't indicate the actual cognitive functioning of the person, but it does demonstrate that a correlation was not found between actual brain changes of Alzheimer's and thyroid levels.
  • Yet another study found that hypothyroidism was not correlated with an increased risk of mild cognitive impairment. The researchers note that these results assume that hypothyroidism had been treated and thus that there does not appear to be any long-term effects on cognitive functioning.
  • In a study of participants with Hashimoto's disease (the most common cause of hypothyroidism), younger adults who were adequately treated did not show any significant difference in cognitive functioning from those whose thyroid functioning was normal.

In short, while the research doesn't all agree, several studies indicate that major cognitive problems are not likely to develop with hyperthyroidism or hypothyroidism. They also conclude that minor cognitive problems associated with thyroid functioning are often temporary.

Thus, if major cognitive decline is present, the physician should conduct a comprehensive assessment to determine what other medical conditions may be affecting your functioning.

Does Thyroid Treatment Help You Think More Clearly?

Fortunately, there is an effective treatment available for those with thyroid problems. The thyroid hormone levels can be adjusted through the use of oral medications, radioactive iodine, and/or surgeries.

So, can this treatment help people with thyroid disorders who are experiencing cognitive problems? Although there is some question of the effectiveness of treatment with significantly older adults, most research shows that cognitive functioning improves when thyroid disorders are treated.

In fact, the good news according to the Rancho Bernardo study is that people who've been treated with supplemental thyroid therapy show no decline in cognitive functioning.

A Word From Verywell

If you're experiencing forgetfulness or difficulty concentrating along with your thyroid concerns, be sure to convey these issues to your physician. While you might initially feel embarrassed or uncomfortable about your brain fog, remind yourself that sharing this knowledge with your doctor helps the two of you be more effective as you work towards the goal of restoring your normal functioning. 

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