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The Thyroid and the Brain
The thyroid and the brain
©Freepik

The brain is the most complex organ of the human body and has a remarkable ability to functionally restructure and adapt throughout life. In response to learning, experience, injury, or environmental influences, this three-pound mass can reorganize its structure and the connections (between brain cells) and induce a functional change in these cells. This phenomenon is known as neuroplasticity, and it enables us to learn new skills, form memories, develop new habits, recover from brain injuries, and adapt to changes in our environment. 

Thyroid hormones, released by the thyroid gland, regulate various bodily functions, including metabolism, heart rate, and body temperature. Interestingly, research shows that thyroid hormones also influence neuroplasticity. A study published in Acta Neuropathologica Communications in 2019 investigated the role of triiodothyronine (T3), the active form of the thyroid hormone, in promoting neuroplasticity after a stroke. Following a stroke, the undamaged areas of the brain can take over some of the functions originally handled by the damaged area. This study’s findings highlight T3 as a promising therapeutic agent with the potential to help people regain brain function after a stroke caused by blocked blood flow.

Overall, thyroid hormones play a significant role in both brain development and adult brain function, and these will be discussed in the rest of this article. We will also take a look at how the brain and thyroid are linked through the hypothalamic-pituitary-thyroid (HPT) axis, as well as the connection between thyroid dysfunction and some neurological conditions.

The hypothalamic-pituitary-thyroid (HPT) axis: How are the brain and thyroid linked?

The thyroid gland communicates with the brain through a feedback loop involving the hypothalamus and the pituitary gland. This complex feedback loop is known as the hypothalamic-pituitary-thyroid (HPT) axis. The hypothalamus, a part of the brain, produces thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland, located at the base of the brain, to release thyroid-stimulating hormone (TSH). TSH, in turn, stimulates the thyroid gland to produce and release thyroxine (T4) and triiodothyronine (T3). Once produced, T4 is converted into the more active T3 in various tissues throughout the body, including the brain.

When thyroid hormone levels are too low, the hypothalamus and pituitary gland increase TRH and TSH production, respectively, to stimulate thyroid hormone synthesis. Conversely, elevated thyroid hormone levels suppress TRH and TSH production, preventing excessive thyroid hormone secretion. 

These feedback mechanisms ensure that thyroid hormone levels remain within a narrow range to maintain homeostasis. Disruptions in this feedback loop can lead to thyroid disorders, such as hypothyroidism and hyperthyroidism, which can significantly affect brain function and mental health.

What is the thyroid’s role in brain development?

One fascinating thing about the thyroid is how its crucial impact starts even before you’re born. Thyroid hormones are important for proper brain development, particularly during fetal development and infancy. These hormones influence the growth and migration of brain cells, the formation of connections between them, and the development of myelin, a fatty sheath that insulates nerve fibers and helps them transmit signals efficiently.  

Without sufficient thyroid hormone from the mother during this sensitive period, the development of the fetus’ brain can be hampered, potentially leading to cognitive problems after childbirth. For this reason, iodine intake is especially critical during pregnancy. According to the World Health Organization (WHO), pregnant women need more iodine than usual to ensure that their developing baby gets enough. However, it is important to note that although congenital hypothyroidism can be caused by iodine deficiency in the pregnant mother, it can also be caused by an excessive dietary intake of iodine during pregnancy, according to a study published in The Journal of Paediatrics in 2012. To stay on the safe side, the WHO suggests a maximum daily iodine intake of 500 micrograms for pregnant women. 

How does the thyroid affect the adult brain?

The impact of thyroid hormones doesn’t stop after childhood. They continue to regulate various brain functions throughout adulthood, including the circadian rhythm. This is the body’s “internal clock,” which guides your sleep-wake cycle, telling your body when to feel sleepy and awake. Thyroid hormones also influence mood and cognition. Here’s how:

1. Thyroid Hormones and Emotional Well-being

The thyroid gland influences emotional well-being and mood regulation. Thyroid hormones influence the production and activity of neurotransmitters such as serotonin, dopamine, and norepinephrine, which play crucial roles in regulating mood and emotions. Imbalances in thyroid function can contribute to anxiety and mood disorders such as depression.

Hypothyroidism in particular is commonly associated with symptoms of depression, fatigue, and lethargy. These symptoms can significantly impact an individual’s quality of life and functioning. Moreover, thyroid dysfunction may exacerbate existing psychiatric conditions such as depression and anxiety disorders, making accurate diagnosis and treatment of thyroid disorders essential for optimal mental health outcomes.

2. Thyroid Hormones and Cognitive Function

Throughout life, thyroid hormones also influence cognitive function, including learning and memory. Both hypothyroidism and hyperthyroidism can impair cognitive performance, albeit through different mechanisms.

In hypothyroidism, decreased thyroid hormone levels can lead to symptoms such as forgetfulness, poor concentration, slowed thinking, and difficulty processing information. These cognitive impairments often improve with thyroid hormone replacement therapy. This underscores the importance of maintaining optimal thyroid function for cognitive function.

Conversely, excessive thyroid hormone levels, characteristic of hyperthyroidism, can overstimulate the central nervous system, leading to cognitive symptoms such as racing thoughts, poor attention, and impaired decision-making.

Thyroid Disorders and Neurological Conditions

Thyroid disorders have also been linked to various neurological conditions, such as:

1. Alzheimer’s Disease: Some studies suggest that hypothyroidism may be a risk factor for Alzheimer’s disease, a progressive neurodegenerative disorder. Thyroid hormones play a role in the metabolism of amyloid beta, the protein implicated in the pathology of Alzheimer’s disease. Interestingly, in an article recently published in the Cell and Molecular Neurobiology journal in 2023, the authors extensively reviewed scientific literature that points to the bidirectional impact hypothyroidism and Alzheimer’s disease have on each other. 

2. Bipolar Disorder: There is some scientific evidence suggesting that disruptions in the HPT axis play a role in bipolar disorder (also known as bipolar affective disorder). Hypothyroidism, in particular, is commonly observed in people with bipolar disorder. Interestingly, lithium treatment, while effective for bipolar disorder, can worsen or induce hypothyroidism. For this reason, it is important to monitor thyroid function in patients undergoing treatment for bipolar disorder. High-dose thyroxine supplementation may be considered for some treatment-resistant cases.

3. Migraines: A migraine is one of the most common neurological conditions, affecting more than 10% of the global population. It is mainly characterized by recurrent episodes of severe headaches that cause throbbing or pulsing pain on one side of the head. Thyroid disorders, particularly hypothyroidism, have been linked to an increased risk of migraines. The exact mechanisms underlying this association are not fully understood but may involve alterations in neurotransmitter levels and vascular function.

Kindly note that…

  • If you’re experiencing symptoms that could be related to thyroid problems, it’s important to get tested by your doctor. 
  • A thyroid function test can help determine if you indeed have a thyroid problem.
  • An early  diagnosis and treatment can make a big difference in managing your thyroid health and safeguarding your brain function.

Key Takeaways

  • Unlike other organs, the brain isn’t “static” or “fixed” but rather dynamic and capable of continuously reshaping itself. Neuroplasticity allows our brains to adapt to new situations, form new memories, and even recover from injuries.
  • Thyroid hormones play a crucial role in brain development, particularly during fetal development and early childhood. A pregnant woman’s thyroid hormone supply nourishes the developing baby’s brain until its own thyroid gland takes over.
  • In adults, these hormones continue to influence brain function, including mood, cognition, and memory. 
  • Disruptions in thyroid function can have significant implications for brain health, affecting cognitive function, mood, and potentially increasing the risk of neurological conditions. 
  • Maintaining optimal thyroid health is crucial for preserving brain health and overall well-being. If you suspect you have a thyroid disorder, consult with a healthcare professional for proper diagnosis and treatment.

Disclaimer

At ThyForLife, we do our utmost to provide accurate information. For detailed medical information regarding diagnosis, treatment, and general practices please consult your healthcare professional. Always listen to the advice of your healthcare provider.
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