An underactive thyroid, commonly known as hypothyroidism, is an extraordinarily common condition affecting about 20 million Americans. Optimal thyroid functioning is critical, as the thyroid affects every system in the body. In fact, it's so important that it is one of the conditions that newborns are screened for shortly after birth because too low or too high thyroid hormone at this age could be detrimental to life.

This article will discuss hypothyroidism, its causes, and common signs and symptoms. Additionally, hypothyroidism testing and integrative treatment options will be discussed.

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What is Hypothyroidism?

Hypothyroidism occurs when the thyroid gland in the neck does not make enough thyroid hormones. Thyroid hormones are used by every cell in the body, meaning hypothyroidism has an array of systemic effects.

The Hypothalamic Pituitary Thyroid (HPT) axis is a feedback loop that controls thyroid function. When the body requires more thyroid hormone, the hypothalamus releases Thyroid-Releasing hormone (TRH) to the pituitary gland, which sends its hormone, Thyroid Stimulating Hormone (TSH), to the thyroid gland. In response, the thyroid will make two primary hormones, thyroxine (T4) and triiodothyronine (T3). T4 is the primary hormone produced, but T3 is more metabolically active. T4 must be converted to T3, and this occurs in peripheral tissues such as the liver and kidney. Additionally, T4 can convert into another hormone, reverse T3 (rT3), which is metabolically inactive.

The amount of circulating thyroid hormones sends a feedback signal to the hypothalamus in the brain, and further output of TRH and TSH are dependent upon this amount. Therefore, under normal conditions, when the thyroid hormone supply is sufficient, TSH release is sustained. When thyroid hormones are low, and the body is in need, the hypothalamus senses the low level, and HPT activation occurs, leading to an increase in TSH. Conversely, when thyroid hormones are high, that will suppress TSH production.

In hypothyroidism, there is a miscommunication in this process. Low thyroid circulating thyroid hormones are sensed by the hypothalamus, leading to elevated levels of TSH. However, in hypothyroidism, the thyroid gland does not respond; thus, thyroid hormones remain low. This presentation of high TSH with low thyroid hormones is indicative of hypothyroidism.

There is a condition called subclinical hypothyroidism, which occurs when TSH is elevated, but thyroid hormones are normal.

What Causes Hypothyroidism?

Hypothyroidism can be caused by surgical removal of the thyroid gland, thyroid gland inflammation (thyroiditis), hypothyroidism present at birth (congenital hypothyroidism), radiation treatment of the thyroid, certain medications, pituitary and hypothalamic disorders, and iodine imbalances. Additionally, the most common cause of hypothyroidism is the autoimmune condition Hashimoto's thyroiditis. Hashimoto's thyroiditis occurs when the immune system mistakes the thyroid gland as a foreign invader and begins attacking it. This results in thyroid gland inflammation and will eventually lead to low thyroid hormone output or hypothyroidism. Hashimoto's thyroiditis is most common in women and seems to be hereditary.  

Certain diseases will increase the risk of hypothyroidism, including type 1 or type 2 diabetes, pernicious anemia, Sjogren's syndrome, Celiac disease, Rheumatoid arthritis, and lupus.

Hypothyroidism Symptoms

Signs and symptoms of hypothyroidism can vary depending on age, sex, and other factors. Common symptoms include fatigue, feeling cold, weight gain, joint and muscle pain, dry skin, hair loss, irregular periods and fertility problems, constipation, shortness of breath, mood changes, and memory problems.

Left untreated, hypothyroidism can lead to myxedema coma, a life-threatening condition requiring immediate medical care. Hypothyroidism can also increase the risk for cardiovascular disease, peripheral neuropathies (nerve damage), infertility, birth defects, and goiters (thyroid gland enlargement).

Ultimate Guide to Hypothyroidism Lab Testing

Most conventional doctors will test for TSH levels to screen for thyroid function and health. However, it is estimated that a TSH screening alone will miss about 7% of overt thyroid disease.

A functional medicine approach will examine a full thyroid panel as well as other specialty lab testing to get a clearer picture of how the body is converting and making thyroid hormones.

Complete Thyroid Panel

A complete thyroid panel, such as the thyroid panel by Precision Point, assesses TSH, T4, T3, free T4, free T3, reverse T3, and thyroid antibodies TPO and Tg. Thyroid testing should be done consistently in the morning, and any patient taking biotin should avoid its use prior to testing, as biotin can falsely alter results.

Comprehensive Stool Testing

A comprehensive stool test, such as GI360 by Doctor's Data, measures short-chain fatty acids (SCFAs), including their byproducts, zonulin (a marker of intestinal permeability), shows levels of numerous microbes of the microbiome, and assesses markers of digestion and absorption, all of which can aid in the evaluation of thyroid functioning. Thyroid hormones and SCFAs strengthen tight junctions in the small intestine, decreasing permeability and thus lessening the prevalence of increased intestinal permeability or "Leaky Gut." With Leaky Gut, the protein zonulin can also damage tight junctions. Zonulin levels are increased in autoimmune diseases such as Hashiomoto's thyroiditis. Also, dysbiosis, or an imbalance of good and bad bacteria in the microbiome, promotes the development of autoimmune diseases. Additionally, the levels of the bacterial family Lactobacillaceae and bacteria species Bifidobacteria, two of the most beneficial microbes in the GI tract, are reduced in Hashimoto's thyroiditis. Lastly, GI functioning includes absorbing nutrients necessary for optimal thyroid functioning.

Small Intestine Bacterial Overgrowth

SIBO testing, such as the Triosmart test by Gemelli Biotek, checks for large amounts of microbes in the small intestine. These microbes are translocated from the microbiome in the large intestine, where they should be. When present in large amounts in the small intestine, they can cause problems such as increased inflammatory markers, destruction of tight junctions, and more. There has been a correlation between SIBO and hypothyroidism, as hypothyroidism can cause lowered gastrointestinal motility, and SIBO symptoms can mimic and exacerbate hypothyroid symptoms. Lastly, as discussed in comprehensive gut testing, SIBO can affect the absorption of nutrients, some of which are implicated in hypothyroidism.

Micronutrient Panel

A micronutrient panel can help to assess thyroid functioning. Many nutrients, including selenium, iron, and vitamin d, are required for proper thyroid physiology; thus, testing levels to ensure adequate levels can be beneficial.

Liver Function Panel

Liver function plays an essential role in thyroid physiology. The liver aids in converting T4 into T3 and is also where these hormones are metabolized. ‍

Other Lab Test to Check

Additionally, the following labs should be ordered as their markers can be affected by hypothyroidism:

• Cholesterol panel: Hypothyroidism can cause elevated cholesterol and triglyceride levels, both of which are risk factors for cardiovascular disease.
• Complete blood count (CBC). Iron is a required nutrient for thyroid hormone synthesis and more, and thus may be deficient in hypothyroidism. Low iron can also cause iron deficiency anemia (IDA), characterized by low red blood cells and low circulating oxygen. A CBC will be able to detect IDA.
• Prolactin: Prolactin is a hormone made by the brain's pituitary gland that causes milk duct activation in the breast tissue. Elevations in TRH and TSH can cause increased production of prolactin.
• Female hormone panel: Thyroid hormones may affect female hormones, fertility, and menstrual cycles due to ovulatory changes. Additionally, elevated prolactin can cause menstrual irregularities.
• Male hormone panel: Lack of thyroid hormones can affect testicular function, including sperm production. Like female hormones, high prolactin may also alter male hormones, sperm, and testosterone production.  

A thyroid ultrasound may be required if abnormal findings are found on a physical exam. Ultrasounds are painless procedures that use sound waves to produce images.

‍Conventional Medicine Treatment for Hypothyroidism

Since the thyroid affects every system of the body, replacement of thyroid hormone in the form of medication is necessary for people with hypothyroidism.

The primary medication recommended for hypothyroidism is levothyroxine, which is synthetic T4. There are also medications containing T3 and medications containing both T4 and T3. Additionally, thyroid hormones can be compounded through a compounding pharmacy.

Thyroid levels will often be rechecked 6-8 weeks after the start of medication. Thyroid medication may then be checked every six months after that.

It's important to note that thyroid medication must be taken alone as nutrients can interfere with absorption. Timing will vary, usually from 30-60 minutes, depending on the type of medication.

Lastly, many patients on thyroid medication still report hypothyroid symptoms. This is where an integrative medicine approach can shine, as integrative therapies can help to alleviate the residual symptoms.

Nutrition for Hypothyrodism

Consider eliminating or reducing gluten. Gluten can increase zonulin levels, a protein found in the GI tract that can damage tight junctions. Zonulin levels are increased in autoimmune patients, so if Hashimoto's thyroiditis is present, it may be wise to eliminate wheat and monitor symptoms for improvement.

Iodine is an essential nutrient for thyroid functioning as it's required to synthesize T4 and T3. However, too much or too little iodine can lead to hypothyroidism. Consuming iodine through foods may be the safest way to ensure proper levels and avoid excess intake and deficiencies. Iodine-rich foods include seaweed, seafood, and iodine-fortified foods such as milk products and salt.

Supplements for Hypothyroidism

Iron, vitamin D, and selenium are all required cofactors for thyroid physiology. Iron is necessary for thyroid cells to utilize iodine and for the production of thyroid hormones. Vitamin D, zinc, and selenium are required to synthesize thyroid hormones properly. Zinc and selenium are necessary for the conversion of T4 into T3. Zinc also aids in the utilization of T3 by cells via its function on receptors. Selenium supplementation has also been shown to reduce thyroid antibody levels and improve the structure of the thyroid gland.  

Magnesium deficiency has also been implicated in hypothyroidism. In a study of over 1,200 Chinese people, magnesium deficiency was associated with a higher rate of Hashimoto’s thyroiditis and hypothyroidism.

As discussed above, the microbiome may play an important role in thyroid physiology. A randomized control trial showed improved TSH and fatigue when a supplement with probiotics and prebiotics was given. Additionally, thyroid medication needed to be lowered.

Summary

The thyroid gland is a vital organ that affects every body system. Hypothyroidism, therefore, can significantly affect a person's quality of life. Proper thyroid testing is essential not only for the diagnosis of hypothyroidism but also for monitoring treatment. As the GI tract, nutrients, and liver function can impact the development of hypothyroidism, labs assessing these symptoms should be done. Additionally, due to the thyroid's system-wide effects, testing outside of evaluating the thyroid gland may also be considered.