Did you know that 1 in 10 Canadians are struggling with a thyroid disorder and don’t even know it?! I see people in my office everyday with ‘mysterious and undiagnosed’ symptoms, or an everyday feeling of ‘blah’. In these cases, the thyroid should always be investigated and is often over looked.
Over the next few weeks I will be giving you a fundamental understanding of the thyroid gland, what it does, how to properly assess it, and how treatment is approached. If you think you, or a loved one, have a thyroid condition this understanding is a MUST. I hope you enjoy!
Fundamental Understanding of the thyroid
What is the thyroid and how does it work?
The term thyroid is derived from a Latin term ‘glandulathyreoidea’. It is one of the vital endocrine glands, secreting hormones that play a crucial role in the growth, maturation, and metabolism of the human body. The rate of hormonal secretion from the thyroid glands depends upon physiological need and environmental factors, for example, there is an increased secretion of thyroid hormone during growing age and pregnancy. The cold weather also enhances the secretion of thyroid hormone.
The thyroid gland is a butterfly-shaped organ located in the anterior part of the neck under the voice box. The right and left lobes of the gland are attached with a tissue strip and adjoins with the windpipe. There are small lobules present inside the thyroid gland containing numerous vesicle like structures known as follicles, which store thyroid hormones in form of tiny droplets. The thyroid gland produces three types of hormones – Triiodothyronine (T3), Tetraiodothyronine or Thyroxine (T4) and Calcitonin. T1 and T2 are also created in the thyroid gland, although the function of these hormones has yet to be determined.
Iodine has a significant role in T3 and T4 production from follicular endothelial cells of the thyroid gland. The required amount of iodine is absorbed from dietary sources and participates in thyroid metabolism. Both T3 and T4 enhance the basal metabolic rate of the body and produce more energy. That being said, T3 is viewed as the ‘active hormone’ and T4 the ‘storage hormone’, more on that later.
The action of thyroid hormones include the following:
- Elevation of body temperature
- Increase in the rate and strength of the heart beat
- Faster food absorption to maintain energy levels
- Promotion of brain development and body growth in growing children
- Activation of the nervous system to improve concentration and reflex actions.
Overproduction and underproduction of these thyroid hormones are clinically denoted as hyperthyroidism and hypothyroidism respectively, and have many abnormal physiological consequences.
Calcitonin, produced by C-cells of the thyroid plays a major role in calcium metabolism and bone health maintenance.
What factors are involved in the conversion from T4 to T3?
TSH (thyroid stimulating hormone) is secreted from the anterior pituitary gland in the brain and directly influences the secretion of thyroid hormones. The more TSH released from the pituitary, the more the thyroid is told to make hormones. A certain amount of Triiodothyronine (T3) is directly secreted from the thyroid gland and reaches the blood stream, but the majority of it comes from the conversion of thyroxine (T4) into T3 . T4 and T3 are structurally different from each other. One extra iodine is present in the T4 structural configuration and the presence of that extra iodine makes it a storage form of the hormone, with minimal activity. T4 is converted to T3 at the tissue level by the deiodinases. The more active form of thyroid hormone is T3, as it binds to thyroid receptors with a greater affinity than T4. Therefore, when looking at the thyroid hormones, we need to consider not only what the thyroid itself is making, but also how well T4 can be converted into the active T3 in the periphery. This conversion is dependent on many things such as environmental factors, diseases, drugs etc.
Both cold and hot environments manipulate thyroid hormone secretion. In lower temperatures, TSH level increase and thus T4 and T3 values become higher. Whereas hot weather decreases serum TSH level and subsequently decreases both T4 and T3 values.
Acute exposure to high altitude or a state of hypoxia leads to the elevation of T4 and T3 values, but regular contact with this environment diminishes TSH secretion while T4 and T3 values drop down. 
Total calorie intake and iodine supply are also essential for maintaining the homeostasis of thyroid hormone. The conversion from T4 to T3 gets interrupted and reduces T3 production during starvation and chronic malnutrition. However, overeating increases the conversion rate of T4 to T3 and further increases T3 level in blood serum.  Apart from iodine, reductions in selenium (another essential mineral) level lead to decreased conversion of T4 to T3 and a decrease in peripheral production of T3.
Physical and Mental Stress
Both physical and emotional stress suppress TSH level and decrease the production of T3 . Long term stress can also increase the production of reverse T3, a protective mechanism in the body. This is also known as euthyroid sick syndrome.
Chemicals and Drugs
Different chemicals including some dietary products contain goitrogens, which inhibit thyroid hormone synthesis by reducing the iodide level available. This reduction consequently enhances the sensitivity of the thyroid gland to TSH and promotes goitrogenicity (AKA enlarging of the thyroid gland in a way not dissimilar to how a muscle grows when it works very hard). Examples of dietary substances which are considered as goitrogens are sorghum, cassava, millet, and maize. Some plants like cabbage, cauliflower, brussel sprouts, kale, horseradish, kohlrabi, turnip, mustard, and rutabaga are also referred as goitrogens. These should all be consumed cooked to minimize the impact on the thyroid gland.
Apart from the above mentioned dietary sources, some drugs also alter thyroid hormone metabolism and inhibit the conversion of T4 to T3. For Example, propylthiouracil (anti-thyroid drug), glucocorticoids (anti-inflammatory and immunosuppressive), propranolol (antiarrhythmic, antihypertensive), amiodarone (antianginal and antiarrhythmic agent), iodinated contrast agents (radiologic contrast media) and clomipramine (tricyclic antidepressant). 
What is hypothyroidism?
An underactive thyroid gland leads to decreased production of thyroid hormone which is known as hypothyroidism. The characteristic features of hypothyroidism lead to decreased rate of body metabolism and causing low energy, tiredness, dry skin, hair loss or constipation. These symptoms may appear with other clinical conditions as well. Therefore, in order to properly diagnose hypothyroidism it is essential to know the underlying cause of these symptoms, and that can only be assessed by an investigative blood test to detect the level of thyroid hormones. 
What is Hashimoto’s?
Hashimoto’s is an organ-specific autoimmune disease that is mediated by T-cells and affects the thyroid. The current understanding of the research notes that Hashimoto’s is a condition with a strong genetic component, and additionally an environmental influence. [7,8]
Symptoms of Hashimoto’s and Hypothyroidism
The primary clinical feature of Hashimoto’s is hypothyroidism . In the initial stage, Hashimoto’s is usually asymptomatic due to subclinical hypothyroidism (No symptoms or mild symptoms of hypothyroidism). But Hashimoto’s is a chronic condition and the symptoms arise when the disease is in a progressive hypothyroidism stage. 
Following are the common symptoms of hypothyroidism:
- Weight gain
- Extreme sensitivity to cold temperature
- Pain in joints and muscles
- Irregular bowel movements or constipation
- Hair loss
- Dull and dry hair
- Irregular menstrual cycle with heavy bleeding
- Difficulty conceiving
- Memory impairment and brain fog
- Slow heart rate
- Abnormal sensation of pharynx **
- Hoarseness ** ***Classic symptomatic feature of Hashimoto’s disease 
- Sore throat **
The above-mentioned hypothyroidism related symptoms do not always appear in Hashimoto’s disease, nor do you have to have all of them in order to have Hashimoto’s. 
The other important thing to note is that during a heightened period of autoimmune attack symptoms of hyperthyroidism can present intermittenedly. This is because the attack of the thyroid glands can result in a ‘dumping’ of thyroid hormone into the blood stream.
Today’s Wrap Up
The thyroid gland is an intricate and complex little system. I always say the thyroid is like the canary in the coal mine because the rate of both thyroid hormone production, and conversion, are drastically affected by a number of factors discussed today. In order for you to feel well, and prevent all of the aforementioned symptoms of hypothyroidism your brain, thyroid, enzymes, thyroid hormone receptors and peripheral tissues have to work together. And the more cooks in the kitchen, the more opportunities for things to go wrong!
Next week we will take off from this point and get into the juicy stuff that I know most of you are waiting for. We will cover how the thyroid should be tested, what exams should be done, and how to get a proper diagnosis. All of these things, and more will be answered! Until then, be well!
References for the series:
- How does the thyroid work? – PubMed health – national library of medicine – PubMed Retrieved from https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072572/
- Lewis E. Bravemman, Sidney H. Ingbar, Keinwem Sterling; Conversion of Thyroxine (T4) to Triiodothyronine (T3) in Athyreotic Human Subjects; The Journal of Clinical Investigation Volume 49 1970; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC535757/pdf/jcinvest00221-0019.pdf
- Amy C. Schroeder, Martin L. Privalsky; Thyroid Hormones, T3 and T4, in the Brain; Front Endocrinol (Lausanne)2014; 5: 40. Published online 2014 Mar 31. doi: 10.3389/fendo.2014.00040; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3978256/
- David Sarne, Effects of the Environment, Chemicals and Drugs on Thyroid Function; Medical Director, Endocrinology and Metabolism Clinics University of Chicago; Last Update: September 27, 2016; https://www.ncbi.nlm.nih.gov/books/NBK285560/
- Olivieri O,Girelli D, Stanzial AM, Rossi L, Bassi A, Corrocher R.; Selenium, zinc, and thyroid hormones in healthy subjects: low T3/T4 ratio in the elderly is related to impaired selenium status; Biol Trace Elem Res. 1996 Jan;51(1):31-41. https://www.ncbi.nlm.nih.gov/pubmed/8834378
- Hypothyroidism – national library of medicine – PubMed . Retrieved from https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0022776/
- Dimitry A Chistiakov; Immunogenetics of Hashimoto’s thyroiditis; J Autoimmune Dis.2005; 2: 1. Published online 2005 Mar 11. doi: 10.1186/1740-2557-2-1; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC555850/
- Hashimoto’s disease – national library of medicine – PubMed . Retrieved from https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0025658/
- Wang Z; [Diagnosis and treatment in 45 patients with Hashimoto’s thyroiditis associated with throat symptoms]; Lin Chuang Er Bi Yan Hou Ke Za Zhi.2003 Feb;17(2):81-3; https://www.ncbi.nlm.nih.gov/pubmed/12833688
- Hashimoto’s disease. (2015, November 17). Retrieved January 12, 2017, from https://www.niddk.nih.gov/health-information/health-topics/endocrine/hashimotos-disease/Pages/fact-sheet.aspx
- Terry J. Smith.; Chapter 138Neck and Thyroid Examination; Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition; https://www.ncbi.nlm.nih.gov/books/NBK244/
- Caturegli P,De Remigis A, Rose NR; Hashimoto thyroiditis: clinical and diagnostic criteria; Autoimmun Rev. 2014 Apr-May;13(4-5):391-7. doi: 10.1016/j.autrev.2014.01.007. Epub 2014 Jan 13; https://www.ncbi.nlm.nih.gov/pubmed/24434360
- Trbojević B,Djurica S.; [Diagnosis of autoimmune thyroid disease]; Srp Arh Celok Lek. 2005 Oct;133 Suppl 1:25-33; https://www.ncbi.nlm.nih.gov/pubmed/16405253
- Clinic, (2016).Mayoclinic. Retrieved from http://www.mayoclinic.org/diseases-conditions/hashimotos-disease/symptoms-causes/dxc-20269764
- Chiovato L,Lapi P, Fiore E, Tonacchera M, Pinchera A.; Thyroid autoimmunity and female gender; J Endocrinol Invest. 1993 May;16(5):384-91; https://www.ncbi.nlm.nih.gov/pubmed/8320432
- Ali J Chakera, Simon HS Pearce, Bijay Vaidya; Treatment for primary hypothyroidism: current approaches and future possibilities; Drug Des Devel Ther.2012; 6: 1–11. Published online 2011 Dec 22. doi: 10.2147/DDDT.S12894; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3267517/
- Jacqueline Jonklaas, Antonio C. Bianco, Andrew J. Bauer, Kenneth D. Burman, Anne R. Cappola, Francesco S. Celi, David S. Cooper, Brian W. Kim, Robin P. Peeters, M. Sara Rosenthal, Anna M. Sawka; Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement; 2014 Dec 1; 24(12): 1670–1751. doi: 10.1089/thy.2014.0028; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4267409/
- Toulis KA,Anastasilakis AD, Tzellos TG, Goulis DG, Kouvelas D.; Selenium supplementation in the treatment of Hashimoto’s thyroiditis: a systematic review and a meta-analysis; 2010 Oct;20(10):1163-73. doi: 10.1089/thy.2009.0351; https://www.ncbi.nlm.nih.gov/pubmed/20883174
- Levothyroxine (by mouth) – national library of medicine – PubMed . Retrieved from https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0010926/?report=details
- McCONAHEY WM,WOOLNER LB, BLACK BM, KEATING FR Jr.; Effect of desiccated thyroid in lymphocytic (Hashimoto’s) thyroiditis; J Clin Endocrinol Metab. 1959 Jan;19(1):45-52; https://www.ncbi.nlm.nih.gov/pubmed/13620732
- Gregory A. Brent; Environmental Exposures and Autoimmune Thyroid Disease; 2010 Jul; 20(7): 755–761. doi: 10.1089/thy.2010.1636; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2935336/
- Serena Tonstad, Edward Nathan, Keiji Oda, Gary Fraser; Vegan Diets and Hypothyroidism; 2013 Nov; 5(11): 4642–4652. Published online 2013 Nov 20. doi: 10.3390/nu5114642; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3847753/
- Jagminder K. Bajaj,Poonam Salwan, Shalini Salwan; Various Possible Toxicants Involved in Thyroid Dysfunction: A Review; J Clin Diagn Res. 2016 Jan; 10(1): FE01–FE03.; Published online 2016 Jan 1. doi: 7860/JCDR/2016/15195.7092; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4740614/
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- Markers of potential coeliac disease in patients with Hashimoto’s thyroiditis Rossella Valentino, Silvia Savastano, Maria Maglio, Francesco Paparo, Francesco Ferrara, Maurizio Dorato, Gaetano Lombardi, Riccardo Troncone; European Journal of Endocrinology (2002) 146 479–483; https://www.ncbi.nlm.nih.gov/pubmed/11916614