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Thyroid Basics: How it Works and How to Optimize Function

Posted by Dr. John Thomas on Jan 10, 2020 3:56:21 PM

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When it comes to monitoring your health, the thyroid isn’t usually the first place you think of checking when you feel off. But did you know the thyroid is your body’s main metabolic hormone control center?

This butterfly-shaped gland is located underneath the Adam’s apple and controls the functions of your brain, heart, digestive system, and more. When this gland functions improperly, chronic conditions may develop due to an overactive or underactive production of hormones. Learning how to balance your thyroid hormones is an essential step for optimization, and it starts with understanding thyroid basics.

Thyroid BAsics 1: Healthy Thyroid Function

Your thyroid runs off of “iodine fuel” from the foods you eat, such as seaweed, lima beans, fish, prunes, eggs, and dairy. The thyroid gland converts iodine into the hormones calcitonin, T4 (thyroxine, or tetraiodothyronine), and T3 (triiodothyronine), which it releases into the bloodstream. While calcitonin helps regulate the calcium in your blood, T3 and T4 play the main roles in regulating the functions of the brain, heart, kidneys, skin, eyes, intestines, and muscles.1,2

Are you missing signs of high cortisol and low thyroid levels? Find out what to  look for.


Thyroid Basics 2: T3 and T4 Hormones

Of the hormones the thyroid produces, 80% is T4 and 20% is T3. Although T4 is the main hormone produced, it is primarily inactive and functions by being converted into T3, which is four times more potent than T4. The levels of thyroid hormones are controlled by the release of thyroid-stimulating hormones (TSH) from the pituitary gland as part of the hypothalamus-pituitary-thyroid (HPT) axis.3 

The commonly used thermostat gauge example can help make sense of how the HPT axis functions and maintains proper body temperature. In this example, the hypothalamus represents a person using a thermostat, the pituitary gland represents the thermostat, and the thyroid represents a furnace.

In an ideal scenario, when a person changes the temperature on a thermostat, the furnace is turned on and heat is produced. Once the desired temperature is reached, a feedback mechanism is triggered and the furnace is turned off, stopping the production of heat.

This is mirrored in the body when the hypothalamus stimulates the pituitary gland via the release of a TSH-releasing hormone (TRH)—just like when the temperature on the thermostat is raised—and initiates the production of T3 and T4. Once a certain threshold of thyroid-produced hormones is reached, similar to when the temperature matches the thermostat, the TRH-secreting neurons in the hypothalamus stop secreting TRH via inhibition and the production of thyroid hormones levels off., 

This cycle is a healthy representation of how the thyroid functions, but what happens if the thyroid stops functioning properly? What are the symptoms?4,

Thyroid BAsics 3: Underactive vs. Overactive 

Have you been feeling unusually cold and tired in the middle of the day? Have you gained a few pounds out of nowhere or felt constipated? If so, you may have a condition called hypothyroidism, which affects about 5% of the U.S. population 12 years and older. Of the 20 million affected Americans, 60% of people who have a thyroid disease aren’t aware of it. 

Hypothyroidism is significantly more common among the general public and affects women five to eight times more than men.6 It is characterized by an underactive thyroid that doesn’t produce enough thyroid hormones. Common symptoms are often vague and can be difficult to pinpoint to one condition. Thus, many people go years without checking their thyroid. Signs that may indicate an underactive thyroid include:

  • Fatigue
  • Weight gain
  • Dry skin
  • Pale, puffy face
  • Constipation
  • Temperature sensitivity

The cause of hypothyroidism includes radiation treatment, autoimmunity, inflammation of the thyroid tissue, improper iodine consumption, and damage to the pituitary gland, to name a few. In each case, there is either an issue with the production of T4 and T3 or the conversion of T4 to T3, or there is an issue at the cell receptor level.7

On the opposite side of the spectrum is hyperthyroidism, where the thyroid is overly active and producing more thyroid hormones than necessary. This condition is caused by an overproduction of T4 commonly seen in Graves’ disease, Plummer’s disease, or thyroiditis. This causes symptoms such as weight loss, rapid heartbeat, anxiety, tremors, and sweating. While not life-threatening, a dysfunctional thyroid gland can have harmful effects on multiple systems of the body.

Related Article: Warning Signs of High Cortisol and Low Thyroid

Thyroid BAsics 4: How to Balance Thyroid Hormones

For individuals who suffer from hyper- or hypothyroidism, medical treatment is the only real long-term answer at the moment. For those who err on the side of stress or are treading the fine line between proper and improper hormone production, supplementing with iodine, selenium, zinc, and L-Tyrosine via a healthy iodine-rich diet can help bring balance to the HPT axis and the thyroid gland. 


Optimizing thyroid function starts with a better understanding of how the gland works and the impact it can have on the body. Since stress can wreak havoc on thyroid function, reducing stress can have a major positive impact on improving basic thyroid functions. Due to the wide range of symptoms that often appear unrelated, thyroid dysfunction can be easily overlooked. Talk to your physician to get a sense of what steps you should take to ensure your thyroid is healthy and operating as it should. Early detection of any imbalances can be mitigated with proper intervention and a thoughtful approach.

 By Dr. John Thomas

high cortisol low thyroid

1   “9 Healthy Foods That Are Rich in Iodine - Healthline.” 2018. https://www.healthline.com/nutrition/iodine-rich-foods. Accessed November 19, 2019.

2  “Thyroid Gland: Facts, Function & Diseases - LiveScience.” 2017. https://www.livescience.com/58771-thyroid-gland-facts.html. Accessed November 19, 2019.

3 “Thyroid Gland: Facts, Function & Diseases - LiveScience.” 2017. https://www.livescience.com/58771-thyroid-gland-facts.html. Accessed November 19, 2019.

4 “How Your Thyroid Works - EndocrineWeb.” 2019. https://www.endocrineweb.com/conditions/thyroid/how-your-thyroid-works. Accessed November 19, 2019.

5 “Control of Endocrine Activity - VIVO Pathophysiology.” http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/basics/control.html. Accessed November 19, 2019.

6 “Hypothyroidism - NIDDK.” 2016. https://www.niddk.nih.gov/health-information/endocrine-diseases/hypothyroidism. Accessed November 19, 2019.

7  "Hypothyroidism - ATA.” 2019. https://www.thyroid.org/hypothyroidism/. Accessed November 19, 2019.



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