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Thyroid Function: Metabolism’s Fire


The thyroid, located in the neck area in front of the trachea and behind the larynx, is an important part of the endocrine system. Thyroid function is important for metabolism.

Thyroid Hormone Synthesis

This butterfly-shaped gland is the “T” in the HPA-T Axis. Thyroid hormones are synthesized through this axis and the hypothalamus and pituitary monitor levels in a feedback loop. Here is the process:

  • the hypothalamus creates thyroid releasing hormone (TRH) to regulate the pituitary
  • the pituitary makes thyroid stimulating hormone (TSH) to regulate the thyroid
  • the thyroid creates thyroid hormone T4 and T3, synthesized from iodine and tyrosine

Thyroid and Balancing Metabolism

Like all hormones, thyroid hormone travels through the bloodstream. These hormones affect many body processes, especially metabolism. Thyroid hormone regulates metabolism in each cell of the body. [5] Optimal thyroid function is like a fire that fuels metabolic function.

Metabolism is the mechanism by which all of the cells in our body get energy. Metabolism includes the breakdown of food/energy sources, using that energy to build all the components our bodies need like proteins and nucleic acids.

Basically, the thyroid controls the fire that burns our food.

Poor Thyroid Health

In some cases, the thyroid does not produce enough thyroid hormone. The once powerful flame has diminished to a flicker. Thyroid function decreases, and thus, the metabolism slows. Slow metabolism can cause many signs and symptoms including:

  • fatigue
  • poor memory
  • weight gain
  • sexual dysfunction
  • low mood
  • hair loss
  • cold extremities [7]

Causes of Low Thyroid Hormone

Low thyroid levels are most commonly caused by iodine deficiency or Hashimoto’s Thyroiditis, an autoimmune condition. [1]

Irregularities in the pituitary gland can also lead to low thyroid levels. [2]

Hypothyroidism can be treated, but must first be diagnosed and measured by a blood test to find levels of TSH and/or T4, T3, rT3 and autoantibodies.

Low Thyroid Function Prevention

Most areas of the world practice large-scale public prevention through universal salt iodization, and promoting consumption of iodine-rich foods such as fish. The World Health Organization and the American Thyroid Association also promote iodine recommendations and supplementation in people who are pregnant or breastfeeding, who need 66% more iodine than before pregnancy or breastfeeding. [6]

Thyroid Statistics, Related Health Issues, and Symptoms

Despite prevention measures, more than 12% of the US population will develop a thyroid condition during their lifetime.

Furthermore, up to 60% of people with thyroid disease are unaware of their condition, perhaps due to the general symptoms that may not be recognized as ow thyroid function.

Undiagnosed thyroid conditions can impact other areas of health, such as:

  • cardiovascular
  • fertility
  • weight management
  • bone health [3, 4]

…not to mention the persistent symptoms of:

  • low mood
  • weight gain
  • fatigue

Poor thyroid function leads to a slowed metabolism, creating signs and symptoms that can have adverse effects on daily activities, causing even more stress that may further decrease metabolism and imbalance the HPA-T Axis.


For optimal metabolic function, prevention of related conditions, and options for alleviating symptoms, test thyroid function and address any irregularities in the HPA-T Axis so you can keep that fire burning!



  1. Garber, J. R., Cobin, R. H., Gharib, H., Hennessey, J. V., Klein, I., Mechanick, J. I., … & Woeber for the American Association of Clinical Endocrinologists and American Thyroid Association Taskforce on Hypothyroidism in Adults, K. A. (2012). Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association.Thyroid,22(12), 1200-1235.
  2. Persani, L. (2012). Central hypothyroidism: pathogenic, diagnostic, and therapeutic challenges.The Journal of Clinical Endocrinology & Metabolism,97(9), 3068-3078.
  3. Prevalence and Impact of Thyroid Disease. (2016). American Thyroid Association. Retrieved from
  4. Sanyal, D., & Raychaudhuri, M. (2016). Hypothyroidism and obesity: An intriguing link.Indian Journal of Endocrinology and Metabolism,20(4), 554.
  5. Vaitkus, J. A., Farrar, J. S., & Celi, F. S. (2015). Thyroid hormone mediated modulation of energy expenditure.International journal of molecular sciences,16(7), 16158-16175.
  6. World Health Organization, UNICEF, & International Council for Control of Iodine Deficiency Disorders. (1996). Recommended iodine levels in salt and guidelines for monitoring their adequacy and effectiveness. Geneva: WHO.
  7. Yu, J., Tian, A. J., Yuan, X., & Cheng, X. X. (2016). Subclinical Hypothyroidism after 131 I-Treatment of Graves’ Disease: A Risk Factor for Depression?. PloS one11(5), e0154846.

Clinical Contributor

Emily Harrill

Clinical Support Specialist at Sanesco International, Inc.

Emily Harrill is our newest Clinical Support Specialist, and a graduate of UNC Asheville with a Bachelor of Science in Health and Wellness Promotion. Improving quality of life for others is her ultimate goal. She enjoys being a part of the team at Sanesco, exploring wellness through the HPA-T Axis and encouraging others to use holistic, integrative means to achieve balanced health. She loves participating in challenging, empowering, and fun activities – especially Olympic weightlifting and belly dance.

Ramona Richard, MS, NC

Ramona Richard, MS, NC

Ramona Richard graduated with honors from the University of California with a Bachelor’s Degree in psychology and graduated summa cum laude with a Master’s Degree in Health and Nutrition Education. She also holds a Standard Designated Teaching Credential from the State of California, is a California state-certified Nutrition Consultant and a member of the National Association of Nutrition Professionals.

Ramona has participated in nutrition education in both public and private venues, including high school and college presentations, radio and public speaking for the past 20 years. She is the owner of Radiance, a nutrition consulting company, the Director of Education for Sanesco International, and a medical technical writer.

Disclaimer: The information provided is only intended to be general educational information to the public. It does not constitute medical advice. If you have specific questions about any medical matter or if you are suffering from any medical condition, you should consult your doctor or other professional healthcare provider.

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