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The thyroid is a small, butterfly-shaped gland located at the front of the neck. Despite its small size, however, the thyroid plays an important role in many key processes throughout the body. It influences metabolism, helps to regulate body temperature, and aids in growth and development.
Under normal circumstances, the thyroid secretes optimal levels of two hormones, thyroxine or T4, and triiodothyronine, or T3. Outside the thyroid, in organs such as the liver, kidneys, and brain, T3 is also converted from T4. Both T3 and T4 are stored in certain amounts within the thyroid, and when it is needed by the body, the gland secretes the hormones into the bloodstream to meet the cells’ metabolic needs. 
In certain cases, the thyroid is unable to produce sufficient critical hormones. Known as hypothyroidism, this condition can spur a chain reaction in which a number of body-wide symptoms arise. Here, we take a closer look at hypothyroidism, including its causes and treatments.
At the most basic level, hypothyroidism refers to an underactive thyroid. In individuals with hypothyroidism, the thyroid gland cannot produce enough thyroid hormone to keep the body functioning normally. Doctors can confirm hypothyroidism based on symptoms and blood test results. Blood tests may measure thyroid-stimulating hormone (TSH), which is used as a messenger from the pituitary gland to tell the thyroid how much thyroid hormone to produce. When TSH is low, it signals the thyroid to slow down hormone production. This essentially slows down all of the body’s functions, causing you to experience a number of seemingly unexplainable symptoms. 
The symptoms of hypothyroidism can develop slowly over time. In many cases, patients experience weight gain, despite maintaining a regular diet or even eating less than normal. Because the thyroid regulates body temperature, another common symptom of hypothyroidism includes increased sensitivity to cold. Fatigue, dry skin, hoarseness, constipation, and muscle weakness may also ensue.
Since the hormones produced by the thyroid have body-wide effects, symptoms are rarely isolated. Some of the other widespread symptoms patients tend to notice include:
The thyroid is also a part of the endocrine system, which includes the ovaries in women and the testicles in men. With hypothyroidism, symptoms such as heavy or irregular periods may occur. The condition can also lead to fertility issues, as improper hormone levels could affect ovulation.
The challenge with hypothyroidism lies in the fact that the signs and symptoms may be difficult to notice at first, and can vary based on the condition’s severity. Symptoms such as fatigue and weight gain may creep up slowly, and are often attributed to the natural aging process. Nonetheless, symptoms tend to become more pronounced as the metabolism continues to slow.
In some cases, the root cause of this chain reaction is easy to pinpoint. Thyroid surgery, for example, will likely lead to diminished production of hormones by the thyroid. There are other potential causes behind hypothyroidism, however, which are discussed below.
While there are many potential causes behind hypothyroidism, the most common is autoimmune disease. In particular, an autoimmune disorder known as Hashimoto’s thyroiditis is the most common reason behind an underactive thyroid. In this condition, the immune system attacks the thyroids, resulting in inflammation of the gland and an inability to produce sufficient hormones. While it is unknown why certain individuals produce antibodies that target the thyroid gland, this condition often runs in families. It tends to occur in middle-aged women, but it can affect individuals of any age, including men and children.  Another autoimmune disorder that can affect the thyroid includes atrophic thyroiditis.
As mentioned above, thyroid surgery can also result in hypothyroidism. If all or a large portion of the thyroid is removed, it typically results in a lifelong need for thyroid hormones. Radiation therapy to treat cancers of the head and neck may also lead to hypothyroidism.In addition, there are some cases in which medications can contribute to hypothyroidism. For one, patients being treated for hyperthyroidism, in which the thyroid produces too much thyroid hormone, may over-respond to medications. Radioactive iodine or anti-thyroid medications are implemented to restore normal thyroid function, but in pursuit of correcting hyperthyroidism, it’s possible to lower thyroid production too much, causing hypothyroidism. In addition, lithium, which is commonly used to treat psychiatric disorders such as bipolar disorder and mania, can also cause hypothyroidism.
Hypothyroidism can be caused by the following:
While rare, hypothyroidism can also result from other conditions. For example, congenital hypothyroidism, in which a baby is born with a missing or defective thyroid gland, can occur. Most states require thyroid screening in newborns to assess for this condition. Failure of the pituitary gland, which may be a result of a benign tumor, can also lead to insufficient TSH, and subsequently, hypothyroidism. Some women also experience hypothyroidism during or after pregnancy. Finally, the condition can also be caused by an iodine deficiency. Although rare in many parts of the world, the addition of iodine to table salt has almost altogether eliminated the deficiency in the U.S.
Certain populations face an increased risk for hypothyroidism, including women and individuals over the age of 60, as well as people with a family history of the condition. Other autoimmune diseases, including type 1 diabetes and celiac disease, appear to be associated with a higher risk for hypothyroidism as well. 
Diagnosing and treating hypothyroidism is important, as leaving it unaddressed can lead to a number of complications. In an attempt to prompt the thyroid to produce more hormones, the pituitary gland will make more TSH. This constant stimulation can lead to an enlargement of the gland, known as a goiter. While not typically uncomfortable, a pronounced goiter may lead to swallowing or breathing difficulties.
In individuals with an underactive thyroid, increased levels of low-density lipoprotein, also known as the “bad” cholesterol, may occur. This can increase the risk for cardiovascular complications, including heart disease and failure. Depression and peripheral nerve damage may also occur. A rare but life-threatening condition caused myxedema can also result from prolonged, untreated hypothyroidism, and is characterized by severe drowsiness, intolerance to cold, and potentially, unconsciousness.
Luckily, treatments are available to combat hypothyroidism. Typically, the synthetic thyroid hormone levothyroxine is used daily to restore hormones to their appropriate levels. This hormone is identical to the hormone the thyroid produces naturally. It can also help alleviate or reverse the signs of hypothyroidism. Finding the right dose may require some trial and error, so medical professionals perform further blood tests a few weeks after introducing hormones. 
In addition to using medications, certain lifestyle changes, including adopting a diet for hypothyroidism, may help control symptoms.
Dietary changes alone won’t restore normal functioning in the thyroid, and aside from an iodine deficiency, eating habits are unlikely to cause hypothyroidism by themselves. With that being said, diet can have a significant impact on symptoms in individuals with hypothyroidism. While certain foods can improve symptoms, others may worsen them or interfere with medications.
Widely recognized for their health benefits, cruciferous vegetables such as broccoli, Brussels sprouts, collards, cauliflower, cabbage, and Russian kale with plenty of fiber, vitamins, minerals, and phytochemicals and relatively few calories, have been linked to benefits such as protection against cancer.  Yet, they also contain goitrogens which, in some hypothyroid scenarios, are not heavily advised to be consumed in excess.
Nonetheless, having hypothyroidism doesn’t necessarily mean you must avoid cruciferous vegetables altogether. These foods are part of a well-rounded diet and can usually be enjoyed sparingly, since experts believe goitrogens may only impact hormone levels when eaten in excess. Moreover, cooking can deactivate the effects of goitrogens. Individualized lifestyle modifications such as these can be beneficial not only for hypothyroidism, but also any health issues affected by diet. 
Soy is also believed to affect the thyroid when consumed in excess. Soy products include soy milk, soy sauce, edamame, tofu, and miso. For this reason, enjoying these foods only in moderation, especially if you have a known thyroid condition, is recommended. Processed foods that can promote weight gain, which is a common struggle in hypothyroidism, should also be avoided.
At the other end of the spectrum, foods with the nutrients iodine, selenium, and zinc can help maintain optimal thyroid function. Iodine-rich foods include eggs, milk, cheese, and saltwater fish. Selenium, which aids in the production of thyroid hormones, is found in Brazil nuts, turkey, chicken, beef, and tuna, along with eggs and oatmeal. Zinc can be found in oysters, crab, beef, pork, legumes, and yogurt.
If you’re experiencing fatigue, slow weight gain, or any of the other symptoms described herein, it’s a good idea to discuss a potential thyroid issue with a medical expert. While there’s no guarantee hypothyroidism could be behind your symptoms, ruling out this or any other root cause is important to optimizing your quality of life, both now and into the future.
In fact, wellness optimization is at the forefront of what we do at Cenegenics. We believe that to feel one’s best and minimize disease risk, we must establish a complete patient profile, compiling data from factors like hormone levels and other key indicators. With this knowledge, we make informed and individualized treatment recommendations to help our patients maintain the greatest possible level of wellness. For many individuals, our strategic, patient-oriented approaches such as dietary modifications and hormone replacement where clinically indicated can make a life-changing difference in restoring energy, regulating weight, and enhancing overall quality of life.
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About the Contributor
Global Director of Nutrition & Exercise
Rudy Inaba is Cenegenics’ Global Director of Nutrition & Exercise. He is a recognized fitness and sports nutrition consultant with nearly 15 years of experience in clinical exercise physiology and lifestyle management. After pursuing his Master of Science in Clinical Exercise Physiology at the University of Nevada Las Vegas, Rudy joined Cenegenics where he leads 20 clinical locations nationwide in their advancements in kinesiology, nutritional biochemistry, and their analyses of industry research & market trending.
This guide was produced with contributions from the following key resources:
The Cenegenics Education and Research Foundation
The Textbook of Age Management Medicine Volume 1: Mastering Healthy Aging Nutrition, Exercise and Hormone Replacement Therapy
Jeffrey Park Leake, M.D., CPT
Dr. Jeffrey Park Leake is a Partner and Director of Education at Cenegenics Elite Health specializing in age management and wellness. Having trained hundreds of physicians worldwide, Dr. Leake is also the Director of Education for the Clinical Strategies for Healthy Aging course at AMM Educational Foundation.
Todd David Greenberg, M.D., CSCS
Dr. Todd Greenberg is a practicing physician with a broad range of expertise, including wellness, exercise, sports injuries, and MRI of sports injuries. He is a Radiology Clinical Associate Professor at the University of Washington.
 Garber, Jeffrey R., Ph.D. The Harvard Medical School Guide to Overcoming Thyroid Problems. McGraw-Hill.
 Garber; see above.
 “Hashimoto’s Thyroiditis.” American Thyroid Association. Retrieved from URL: https://www.thyroid.org/hashimotos-thyroiditis/
 Mayo Clinic, “Hypothyroidism.” 4 Dec. 2018. Retrieved from URL: https://www.mayoclinic.org/diseases-conditions/hypothyroidism/symptoms-causes/syc-20350284
 Mayo Clinic; see above.
 Wallig, M., et al. Journal of Nutrition, 2005;135(12S):2972S-7S. Steinmetz, K.A., and Potter, J.D., Journal of the American Dietetic Association, Oct. 1996
Marengo, Katherine, LDN, RD. “Hypothyroidism: Foods to eat and avoid.” Medical News Today. 28 Mar. 2019.