The thyroid gland is a small organ located at the base of the neck. When stimulated, the thyroid gland releases two key hormones that regulate different aspects of our body’s metabolism, including, but not limited to:
- Breathing
- Heart rate
- Body weight
- Muscle strength
- Menstrual cycles
- Body temperature
- Cholesterol levels
In addition, the thyroid gland plays an important role in pregnant women, influencing the size and development of the baby’s brain.
Thyroid Anatomy and function
The thyroid gland is a small organ, about 2 inches long, located inside your neck, at the level of your throat, just below the region commonly known as Adam’s apple. The thyroid gland is composed of two lobes that are usually connected by a strip of thyroid tissue known as an isthmus. However, in some people, there is no isthmus, and they have two separate thyroid lobes.
From a functional perspective, the thyroid gland acts as part of a larger hormonal system involving the pituitary gland and the hypothalamus, located in two regions of the brain. In this system, the first actor is the hypothalamus, which produces thyroid-releasing hormone (TRH)1. This hormone stimulates the pituitary gland to release another hormone, called thyroid-stimulating hormone (TSH). TSH then signals the thyroid gland to make T3 and T4 thyroid hormones in two basic ways:
- When there are low T3 and T4 hormone levels, the pituitary gland releases high levels of TSH to signal the thyroid gland to produce more T3 and T4 thyroid hormones.
- When T3 and T4 levels are high, the pituitary gland releases lower levels of TSH, which signal the thyroid gland to reduce the production of T3 and T4 hormones.
Biological function of the Thyroid Gland
The hormones T3 and T4, produced by the thyroid gland, travel in the bloodstream and reach virtually every cell in the body, including the heart, CNS, autonomic nervous system, and bone, where they regulate cell metabolism. Thyroid hormones travel through the bloodstream primarily bound to transport proteins, such as thyroxine-binding globulin (TBG), transthyretin, and albumin. When these hormones reach a target cell, they bind to the cell’s intranuclear receptor, activating the genes involved with increasing metabolic rate and thermogenesis.
Some key organs and structures affected by thyroid hormones include:
Thyroid hormones increase the expression of beta-receptors to increase heart rate, stroke volume, cardiac output, and contractility.
Thyroid hormones can lead to increased oxygenation because of increased perfusion.
Thyroid hormones cause increased development of type II muscle fibres.
During childhood, thyroid hormones act synergistically with growth hormones to stimulate bone growth. It induces chondrocytes, osteoblasts, and osteoclasts.
Thyroid hormones also help with brain maturation by axonal growth and the formation of the myelin sheath.
Some key physiological processes influenced by thyroid hormones include:
- Increasing the basal metabolic rate.
- Potentially inducing lipolysis or lipid synthesis.
- Stimulating the metabolism of carbohydrates.
- Potentially inducing catabolism of proteins in high doses.
- In women, during their prenatal period, thyroid hormones are involved with the maturation of the foetal brain. In adults, thyroid hormones can affect mood.
- Thyroid hormones can affect fertility, ovulation, and menstruation.
Problems with the Thyroid
There are two key Patho-physiologies (malfunctions) of the thyroid gland: over and under production of thyroid hormones. Some of the key features of these two pathologies include:
Hyperthyroidism – or excess of hormone production, which results in abnormally high levels of T3 and T4 hormones, alongside a compensatory decrease of the TSH hormone.
Hypothyroidism – or abnormally low levels of thyroid hormones. There are three types of hypothyroidism.
- Primary hypothyroidism results in low levels of T3 and T4 and a compensatory increase of TSH.
- Secondary hypothyroidism is caused by pituitary disorders leading to decreased TSH release and T3/T4 levels.
- Tertiary hypothyroidism is caused by hypothalamic disorders, resulting in decreased TRH levels, TSH, and T3/T4 levels.
The two most common underlying causes behind altered levels of T3 and T 4 hormones are:
This autoimmune disease is the most common cause of hyperthyroidism. This disease is driven by the production of TSH receptor antibodies, which stimulate thyroid gland growth and thyroid hormone release.
This is the most common cause of hypothyroidism, also caused by autoimmune-mediated destruction of the thyroid gland. Beyond Hashimoto Thyroiditis, other common conditions associated with hypothyroidism include:
- Iodine deficiency
- Cretinism
- Wolff-Chaikoff effect
- Subacute thyroiditis
- Postpartum thyroiditis
- Riedel thyroiditis
- Drug-induced hypothyroidism
In Australia, hypothyroidism is estimated to range from 0.5% to 5%, whereas hyperthyroidism has a prevalence of around 0.5%–1.0%.
Symptoms of Thyroid pathology
Some common symptoms of hyperthyroidism include:
- Heat intolerance
- Weight loss
- Increased appetite
- Increased sweating
- Weakness
- Fatigue
- Onycholysis
- Pretibial myxedema
- Lid lag (when looking down, sclera visible above cornea)
- Lid retraction (when looking straight, sclera visible above the cornea)
- Graves ophthalmopathy
- Diffuse, smooth, non-tender goitre
- Tachycardia
- Palpitations
- An irregular pulse from atrial fibrillation
- Hypertension
- Widened pulse pressure
- Heart failure
- Chest pain
- Abnormal heart rhythms
- Fine tremors in fingers, face, tongue, and head
- Myopathy affecting proximal muscles
- Osteoporosis
- Restlessness
- Anxiety
- Depression
- Emotional instability
- Insomnia
- Hyperreflexia
Some common symptoms of hypothyroidism include:
- Fatigue
- Weight gain
- Puffy, sensitive face
- Depression
- Constipation
- Feeling cold
- Decreased sweating
- Slowed heart rate
- Elevated blood cholesterol
- Dry skin
- Dry, thinning hair
- Impaired memory
- Fertility difficulties or menstrual changes
- Muscle weakness
- Muscle stiffness, aches, and tenderness
- Pain and stiffness in your joints
- Hoarseness
In addition, some complications associated with hypothyroidism include:
- Goitre
- Nerve injury
- Peripheral neuropathy
- Carpal tunnel syndrome
- Reduced kidney function in cases of severe disease
- Myxedema coma, in cases of severe disease
- Obstructive sleep apnea
Thyroid pathology: Nature vs Nurture
According to one study, genetic factors influence about 70% of the pathogenesis of the thyroid, and environmental factors account for the remaining 30%. Genetic factors include particular mutation in the major histocompatibility gene (HLA), immune regulator genes (CTLA4, PTPN22, FOXP3, CD25, CD40, and FRCL3) and thyroid-specific genes (TSHR, Tg).
Beyond autoimmune and genetic factors, altered thyroid function may be caused or influenced by certain environmental factors, like diet, stress, certain environmental toxins and infections, smoking, and a relevant history or radiotherapy or surgery. Some of the most relevant aspects of these factors are:
Micronutrients like iron, zinc, selenium, vitamin E, B vitamins, and iodine are important for the optimal functioning of the thyroid gland.
- Iodine is needed to make thyroid hormones.
- Selenium – deficiency of this mineral impairs thyroid hormone metabolism
- B vitamins – according to one recent study, vitamin B12 deficiency is common among autoimmune thyroid patients. This association may be due to impaired absorption of vit-B12 by atrophic gastritis and/or pernicious anemia associated with autoimmune thyroid disease3.
- Iron, iodine, selenium, and zinc – these trace elements are needed for the synthesis and metabolism of thyroid hormones. Deficiencies of these elements can impair thyroid functions2,4.
During events of chronic stress, there may be an excessive production of glucocorticoids and catecholamines due to activation of the sympathoadrenal system and the hypothalamic–pituitary–adrenal axis (HPA axis), respectively. Altered HPA function due to chronic stress has been linked to altering thyroid hormone secretion, particularly through a role involving corticosterone, the end product of HPA activation5.
Cigarette smoking may affect thyroid function through various mechanisms, including exposure to toxic metabolites, enhanced sympathetic nervous activity, or by affecting thyroid-directed autoimmune responses6.
Some recognised chemicals that affect thyroid function include halogenated organochlorines and pesticides, which can disrupt thyroid function; polychlorinated biphenyls and their metabolites and polybrominated diethyl ethers disrupt thyroid function by binding to thyroid transport proteins7.
Certain viral infections, such as human parvovirus B19 (EVB19) and hepatitis C virus infections, have been associated with autoimmune thyroid diseases7.
High blood levels of cadmium, lead and chromium may increase the risk of developing hypothyroidism and thyroid cancer, according to one study8.
Multiple studies suggest a link between autoimmune thyroid disease and gluten intolerance. In patients with gluten intolerance, their immune system seems to attack thyroid tissue due to structural similarities it has with gliadin, a gluten protein.
Treatment of thyroid dysfunction
If you are experiencing symptoms that could be explained by thyroid dysfunction, a medical practitioner can offer a thyroid blood test that will measure your hormone levels. In addition, an iodine test can be performed to ensure you have healthy levels of this element.
If you have a thyroid dysfunction, the optimal treatment will depend on your condition. People experiencing hypothyroidism, for example, may receive regular inputs of synthetic thyroid hormone levothyroxine. In contrast, if you suffer from hyperthyroidism, you may receive beta-blockers, anti-thyroid medications or other drugs. Surgery is also an option in some cases, where most of the thyroid gland is removed.
Thyroid Function at AUSCFM
At AUSCFM, we follow a modern and evidence-based approach to diagnosing and treating pathologies associated with thyroid malfunction. We are on top of current research on hormones’ role in human health. We employ leading diagnostic testing technologies to hormonal imbalances, as well as other markers of health. Our DUTCH hormone test, for example, provides a comprehensive assessment of key hormones and metabolites. This test informs clinicians about key physiological aspects of your body, such as cortisol and melatonin function, levels of dehydroepiandrosterone, cortisol metabolites, six organic acids and levels of sex hormones. To learn more about the DUTCH hormone test, see our article.
Based on the results of our DUTCH hormone test, we can identify evidence of hormonal imbalances that may be driving your symptoms and identify problems with your thyroid gland. The results of this test, for example, can reveal an altered function of the HPA axis. The Hypothalamic-pituitary-adrenal (HPA) axis is part of the endocrine system and a key regulator of homeostatic processes, influencing immune function and our stress response. To learn more about the HPA axis, see our recent article.
In addition to hormone health, we employ advanced testing that targets six additional gut pathologies. Taken together, the results of these seven tests will give us a comprehensive view of the factors influencing a patient’s health and will help us design personalised treatment strategies.
In parallel, getting an in-depth understanding of your current health and lifestyle, including the diet you follow, can help clinicians identify the root of your problems. Working closely with your practitioner and health coach, you can resolve the underlying cause of hormone imbalance with a personalised plan, including changes to your nutrition, lifestyle, and stress management practices.
If you are experiencing health problems that could be explained by hormonal imbalances, start by registering to
References
- Shahid MA, Ashraf MA, Sharma S. Physiology, Thyroid Hormone. [Updated 2021 May 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 January. Link
- Arthur JR, Nicol F, Beckett GJ. The role of selenium in thyroid hormone metabolism and effects of selenium deficiency on thyroid hormone and iodine metabolism. Biol Trace Elem Res. 1992 Sep;34(3):321-5 Link
- Aktaş, H. Ş. (2020). Vitamin B12 and vitamin D levels in patients with autoimmune hypothyroidism and their correlation with anti-thyroid peroxidase antibodies. Medical Principles and Practice, 29(4), 364-370. Link
- Eftekhari MH, Eshraghian MR, Mozaffari-Khosravi H, Saadat N, Shidfar F. Effect of iron repletion and correction of iron deficiency on thyroid function in iron-deficient Iranian adolescent girls. Pak J Biol Sci. 2007;10:255–6.Link
- Helmreich DL, Parfitt DB, Lu XY, Akil H, Watson SJ. Relation between the hypothalamic-pituitary-thyroid (HPT) axis and the hypothalamic-pituitary-adrenal (HPA) axis during repeated stress. Neuroendocrinology. 2005;81(3):183-92. Link
- Gruppen, E.G., Kootstra-Ros, J., Kobold, A.M. et al. (2020) Cigarette smoking is associated with higher thyroid hormone and lower TSH levels: the PREVEND study. Endocrine 67, 613–622 Link
- Ferrari, S. M., Fallahi, P., Antonelli, A., & Benvenga, S. (2017). Environmental Issues in Thyroid Diseases. Frontiers in endocrinology, 8, 50. Link
- Rezaei M, Javadmoosavi SY, Mansouri B, Azadi NA, Mehrpour O, Nakhaee S. 2019. Thyroid dysfunction: how concentration of toxic and essential elements contribute to risk of hypothyroidism, hyperthyroidism, and thyroid cancer. Environ Sci Pollut Res Int. Link
