WHY IS THYROID FUNCTION IMPORTANT TO THE HUMAN BODY?
The thyroid gland, also known simply as the thyroid, is located in the lower front of the neck just below the Adam’s apple. This small gland is composed of two lobes that are connected by a band of tissue called the isthmus. Because of the positioning of the lobes and the isthmus, the thyroid is often described as butterfly-shaped (1,2).
As part of the endocrine system, the thyroid produces hormones and then releases them into the bloodstream. The two main hormones produced by the thyroid are triiodothyronine (T3) and thyroxine (T4). Both are synthesized primarily from iodine. T3 is the more active form of the hormone, but T4 persists for longer in the bloodstream. This being the case, the thyroid generally produces much greater quantities of T4 so that the hormone can be effectively transported throughout the body. This hormone is then converted to the more active T3 form within organs and tissues that tend to use it most (e.g. the liver, the kidneys, and the brain). The thyroid also produces calcitonin, which helps to control blood calcium levels (1,3).
The thyroid hormones regulate metabolism, the way that energy and nutrients are used, in almost every cell in the body. Processes and systems such as respiration, heart rate, the central and peripheral nervous systems, body weight, muscle strength, menstrual cycles, body temperature, and cholesterol levels are all affected by the T3 and T4 hormones. Because these hormones impact so many of the body’s vital systems and processes, a variety of health problems can occur as a result of thyroid dysfunction (4).
The body uses a feedback system to maintain the thyroid hormone levels within the proper range. The pituitary gland and the hypothalamus, both located at the base of the brain, control the thyroid. When thyroid hormone levels in the bloodstream are too low, the hypothalamus secretes thyrotropin-releasing hormone (TRH). TRH causes the pituitary gland to produce thyrotropin, also known as thyroid stimulating hormone (TSH). TSH stimulates the thyroid to produce more T3 and T4. The resulting increase in T3 and T4 levels feeds back into the hypothalamus, suppressing the production of TRH. Thus, under normal conditions, the levels of thyroid hormones in the blood are constantly monitored and maintained within the proper range.
RISK FACTORS FOR THYROID DISEASE
Risk factors for thyroid disease vary somewhat depending upon the type of the disease. Those that are consistent regardless of the thyroid disease type are:
- Being female. Women are three to eight times more likely to have thyroid problems than men (5,6,7)
- Increased age. While people of any age can develop thyroid disease, the risk of doing so increases with age. Most thyroid cancers affect people after age 20 with risks peaking between age 40 and 70 (6,8). Hypothyroidism occurs most commonly in people over 50 (9)
- Iodine deficiency, which is rare in North America, or excess iodine (7,10)
- Family history of thyroid problems or of autoimmune disease (6,9,10)
- Exposure to heavy radiation especially to the neck and/or upper chest (6,8,9)
A personal history of autoimmune disease (e.g. rheumatoid arthritis, type 1 diabetes, or Addison's disease) is also correlated with increased risk for autoimmune thyroid disease. Pregnant or postpartum women who suffer from autoimmune problems are especially at high risk for developing autoimmune thyroid disease (11,12).
There is some evidence that exposure to certain toxins; like those in pesticides, cigarette smoke, some drugs, and perchlorates may also increase the risk and/or severity of thyroid disease (10,13). This has, however, been difficult to assess in humans and is not unanimously accepted.
SYMPTOMS OF THYROID DISEASE
Some thyroid diseases are associated with thyroid nodules. These nodules are abnormal cell growths on the thyroid that may not ever be noticed by those who have them. In some cases, they can cause difficulty swallowing, pain in the neck, or hoarseness (14).
Goiter, or abnormal enlargement of the thyroid gland, is another symptom associated with many thyroid diseases (15). It is important to note, however, that not everyone with thyroid disease will have a goiter.
Hyperthyroidism, the condition in which thyroid hormone levels are too high, is caused by several thyroid diseases. Symptoms of hyperthyroidism include:
- Thinning of the skin
- Brittle hair and/or hair loss
- Weak muscles, especially in the upper arms and thighs
- Fast heartbeat
- High blood pressure
- Weight loss
- Problems sleeping
- Sensitivity to bright light
- Irregular menstrual cycle in women
- Frequently feeling hot
- Tiredness and lack of energy
- Increased blood pressure (16)
Hypothyroidism, or the condition in which thyroid levels are too low, can also be caused by certain thyroid diseases. Symptoms of hypothyroidism include:
- Frequently feeling cold
- Hoarse voice
- Slow speech
- Droopy eyelids
- Puffy or swollen face
- Weight gain
- Coarse and dry hair
- Hand tingling or pain
- Slow pulse
- Muscle cramps
- Increased or irregular menstrual flow in women (17)
For more information on thyroid disease and diagnosis: 1. Talk to you doctor 2. Visit the American Thyroid Association website 3. Visit the Thyroid Awareness website 4. Visit the You and Your Hormones website
THYROID DISEASE FACTS AND STATISTICS
An estimated 20 million Americans have some form of thyroid disease. (1). Up to 60% of those with thyroid disease are unaware of their condition. Undiagnosed thyroid disease may put individuals at risk for certain serious conditions such as cardiovascular disease, osteoporosis, and infertility. Most thyroid diseases are life-long conditions that can be managed with medical attention (5).
There are two major autoimmune diseases that affect the thyroid: Hashimoto’s thyroiditis and Graves’ disease. In Hashimoto’s thyroiditis, antibodies are errantly directed to attack the thyroid. This leads to a gradual decline in the function of the gland (hypothyroidism) (18). Graves’ disease, on the other hand, is caused by antibodies that bind to and stimulate the thyroid leading overactivity of the gland (hyperthyroidism) (19). Autoimmune inflammation of the thyroid following a pregnancy, a condition known as postpartum thyroiditis, is also common. This kind of autoimmune thyroid problem occurs in approximately 5-10% of women (12).
The four major types of thyroid cancer are: papillary, follicular, medullary, and anaplastic. It’s estimated that approximately 1.2% of people in the US will be diagnosed with one of these cancers at some point during their lifetime (20). Papillary (the most common type), follicular, and medullary thyroid cancers are seldom fatal when treated properly, which usually involves the surgical removal of the tumor. Anaplastic thyroid cancer is relatively rare but is by far the most dangerous type.
MEDICAL TREATMENT AND PREVENTION OF THYROID DISEASE
- Hormone replacement therapies using Levothyroxine (e.g. Synthroid, Levoxyl or Levothroid), Liothyronine (e.g. Cytomel or Triostat), or a mix of the two (e.g. Thyrolar). Side effects often result from misdosing and include irregular heartbeat, increased risk of osteoporosis, and hyperthyroidism (21).
- Hormone suppression therapies using Thiamazole, Methimazole, or Propylthiouracil. Side effects are rare but can include suppression of white blood cell production and subsequent infection (22).
- Surgery to remove nodules, tumors, part of or the whole thyroid.
- Radioactive iodine treatment. Side effects include hypothyroidism, nausea, and salivary gland problems (23).
NATURAL WAYS TO SUPPORT THYROID HEALTH
Practices to Support Thyroid Health:
- Specialized Diets
- Tai Chi (24)
Natural Supplements that Support Thyroid Health:
- Sargis RM. Thyroid gland overview. Endocrineweb. https://www.endocrineweb.com/endocrinology/overview-thyroid. Accessed February 26, 2018.
- What you need to know about the thyroid. American Thyroid Association. https://www.thyroid.org/thyroid-information/. Accessed March 1, 2018.
- About your thyroid. Thyroidawareness.com. http://www.thyroidawareness.com/about-your-thyroid. Accessed March 1, 2018
- Thyroxine. You and Your Hormones: an Education Resource from the Society for Endocrinology. http://www.yourhormones.info/hormones/thyroxine/. Accessed March 1, 2018.
- General information/press room. American Thyroid Association. https://www.thyroid.org/media-main/about-hypothyroidism/. Accessed March 1, 2018.
- Thyroid cancer risk factors. American Cancer Society. https://www.cancer.org/cancer/thyroid-cancer/causes-risks-prevention/risk-factors.html. Accessed March 6, 2018.
- Hypothyroidism - what increases your risk. WebMD article. https://www.webmd.com/women/tc/hypothyroidism-what-increases-your-risk. Accessed March 6, 2018.
- Brady B. Thyroid cancer symptoms, possible causes, and risk factors. Endocrineweb. https://www.endocrineweb.com/guides/thyroid-cancer/thyroid-cancer-symptoms-possible-causes-risk-factors. Accessed March 6, 2018.
- Berber E. Risk factors of hypothyroidism. Endocrineweb. https://www.endocrineweb.com/conditions/hypothyroidism/risk-factors-hypothyroidism. Accessed March 6, 2018.
- Mamula PW. Environmental agents trigger autoimmune thyroid disease. Medscape article. 2010. https://www.medscape.com/viewarticle/722138. Accessed March 6, 2018.
- Thyroid disease & pregnancy. National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/endocrine-diseases/pregnancy-thyroid-disease. Accessed March 6, 2018.
- Pregnancy and thyroid disease. American Thyroid Association. https://www.thyroid.org/thyroid-disease-pregnancy/. Accessed March 6, 2018.
- Manji N, et al. Influences of age, gender, smoking, and family history on autoimmune thyroid disease phenotype. JCEM. 2006;91(12):4873-4880. doi:10.1210/jc.2006-1402.
- Thyroid nodules. UC San Diego Health. https://health.ucsd.edu/specialties/endo/thyroid/Pages/Thyroid-Nodules.aspx. Accessed March 6, 2018.
- Goiter. American Thyroid Association. https://www.thyroid.org/goiter/. Accessed March 6, 2018.
- Hyperthyroidism. UC San Diego Health Library. http://myhealth.ucsd.edu/Search/85,P00408. Accessed March 6, 2018.
- Hyperthyroidism. UC San Diego Health Library. http://myhealth.ucsd.edu/Search/85,P00412. Accessed March 6, 2018.
- Hashimoto’s thyroiditis. American Thyroid Association. https://www.thyroid.org/hashimotos-thyroiditis/. Accessed March 1, 2018.
- Grave’s disease. American Thyroid Association. https://www.thyroid.org/graves-disease/. Accessed March 1, 2018.
- Cancer stat facts: thyroid cancer. National Cancer Institute. https://seer.cancer.gov/statfacts/html/thyro.html. Retrieved March 1, 2018.
- Mathyr R. Hypothyroidism (symptoms, diet, natural and medical treatments, tests). RxList. https://www.rxlist.com/hypothyroidism/article.htm#hypothyroidism_definition_and_facts. Accessed March 7, 2018.
- Stoppler MC and Mathur R. Hyperthyroidism. RxList. https://www.rxlist.com/hyperthyroidism/article.htm#hyperthyroidism_definition_and_facts. Accessed March 7, 2018.
- Milas K. Radioactive iodine for hyperthyroidism. Endocrineweb. https://www.endocrineweb.com/conditions/hyperthyroidism/radioactive-iodine-hyperthyroidism. Accessed March 7, 2018.
- Complementary and Alternative Medicine in Thyroid Disease (CAM). American Thyroid Association. https://www.thyroid.org/thyroid-disease-cam/. Accessed August 10, 2018.
- Kim D. The Role of Vitamin D in Thyroid Diseases. Int J Mol Sci. 2017 Sep; 18(9): 1949. doi:10.3390/ijms18091949
- Sun X, Shan Z, Teng W. Effects of Increased Iodine Intake on Thyroid Disorders. Endocrinol Metab (Seoul). 2014 Sep; 29(3): 240–247. doi:10.3803/EnM.2014.29.3.240
- Betsy A, Binitha MP, Sarita S. Zinc Deficiency Associated with Hypothyroidism: An Overlooked Cause of Severe Alopecia. Int J Trichology. 2013 Jan-Mar; 5(1): 40–42. doi:10.4103/0974-7753.114714.