Thyroid and Cognitive Function

How do thyroid hormones affect brain function, mood and cognition?

Science has been aware of the relationship between thyroid function and brain function for quite some time. Thyroid imbalance very commonly manifests as emotional and/or behavioral change. For instance, depression, inability to concentrate, “foggy brain” can be seen in patients with Hypothyroidism (low thyroid function) whereas anxiety can be one of the common symptoms of Hyperthyroidism.

At the cellular level. The emotions we experience (depression, anxiety) are very often the outward representation of processes and interactions at the cellular and chemical level in the brain. There are different aspects of brain function that could be affected negatively by imbalances in thyroid function. For example:

  1. Levels of serotonin (feel good chemical in the brain) can see a decrease in Hypothyroid patients.
  2. Decrease in the sensitivity of brain cells to Serotonin and other neurotransmitters.
  3. Negative effect on the function of macroglia, which are the most abundant type of brain cell and as such important in brain development as well as healthy adult brain aging. Thyroid hormones moderate the function of macroglia in the brain.

Thyroid function and its relationship to Alzheimer Disease (AD): What research tells us.

Dementia can be a manifestation in patients with clinically low or high Thyroid Stimulating Hormone (TSH). Dementia in this group of patients is reversible when treated with Thyroid Replacement Therapy.

On the other hand, when looking into individuals with normal TSH levels and otherwise normal thyroid function, the Framingham Study (Departments of Medicine and Institute for Aging Research, Hebrew SeniorLife, Beth Israel Deaconess Medical Center & Harvard Medical School, Boston, MA) found a relationship between the TSH levels and risk of developing Alzheimer’s disease.

Study design: In this study, serum levels of TSH in 1864 participants (59%, women), with no known thyroid disease was measured. At the time no participant had any indication of any cognitive issues. Participants were followed for an average of 12.7 years (1-25 years)

Study conclusion:

  • 209 subjects (142 women) developed Alzheimer’s disease
  • Women with serum TSH concentrations <1.0 mU/L and >2.10 mU/L had a >2-fold higher risk of developing AD. Normal ranges for TSH= 0.45-4.5 mU/L
  • The same association was not noted for men.
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