Written byDr. Olivia Rose, ND

The hypothalamic-pituitary-thyroid axis (HPT), an important part of the neuroendocrine system is responsible for the body’s response to stress and for maintaining an overall balance in the release of thyroid hormone.¹ Thyroid hormone is crucial for regulating your metabolism, heart rate and body temperature.¹ When there is an inadequate amount of thyroid hormone released or if there is an issue with the conversion of T4 to the active thyroid hormone T3, this can lead to a plethora of symptoms including constipation, fatigue, weight gain, chills, infertility and dry skin.²

The HPT axis works tightly with the hypothalamic-pituitary-adrenal (HPA) axis. The adrenal glands secrete the stress hormone, cortisol. When levels of cortisol are high, it can cause a disruption at the level of the thyroid gland.^3,4 Cortisol inhibits the production of TSH and directly decreases the amount of thyroid hormone in the body through inhibiting the conversion of the inactive form of thyroid hormone (T4) to the active form (T3).^3,4

Physiological stress includes more than full schedules and anxious thoughts. Stress is a general term which can have many causes including infections, trauma, nutrient deficiencies, inflammation, toxins, and chronic disease. Therefore, environmental toxins such as pesticides, chemicals in plastics and heavy metals may negatively impact the thyroid and throw hormones off-balance.

In an increasingly toxic world, the accumulating metabolic burden can alter hormonal function. The average woman uses 12 personal care products each day, with 168 unique chemical ingredients.⁵ With more than 50% of the metabolism and conjugation of estrogens taking place in the liver, that is not a good sign for women’s health.⁶

The liver also plays an important role in hormone balance, by breaking down and removing excess hormones and their metabolites from the body. This process can be slowed by the accumulation of toxins, leading to the poor metabolism of estrogen and other hormones⁶.The result is hormonal imbalances which negatively impacts the menstrual cycle.

Although most women could benefit from increasing the efficiency of detoxification in the liver, it is always a good idea to test your hormones before supplementing to target the specific issue. Performing a full blood thyroid panel for example, can give you and your healthcare practitioner more information about what is really going on within the HPT axis. Current guidelines suggest that TSH levels should be within the range of 0.4-4mIU/L.⁸

References

1. Helmreich DL, Parfitt DB, Lu XY, Akil H, Watson SJ. Relation between the hypothalamic-pituitary-thyroid (HPT) axis and the hypothalamic-pituitary-adrenal (HPA) axis during repeated stress. Neuroendocrinology. 2005;81(3):183-92.
2. Shahid MA, Ashraf MA, Sharma S. Physiology, Thyroid Hormone. [Updated 2020 May 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK500006/
3. Zoeller RT, Tan SW, Tyl RW. General background on the hypothalamic-pituitary-thyroid (HPT) axis. Critical reviews in toxicology. 2007 Jan 1;37(1-2):11-53.
4. Mariotti S, Beck-Peccoz P. Physiology of the hypothalamic-pituitary-thyroid axis [Updated 2016 Aug 14]. Endotext [Internet]. South Dartmouth (MA): MDText. com, Inc. 2000.
5. Environmental Working Group. 80 Years Later, Cosmetics Chemicals Still Unregulated.  Accessed Feb 11, 2020.  https://www.ewg.org/news-and-analysis/2018/06/80-years-later-cosmetics-chemicals-still-unregulated
6. Relationship Between Hypothalamus and Pituitary Gland - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Anterior-Pituitary-Complex_fig3_320413589 [accessed 14 Aug, 2020]
7. Cui J, Shen Y, and Li R (2013) Estrogen synthesis and signaling pathways during ageing: from periphery to brain. Trends Mol Med. March; 19(3): 197–209
8. American Thyroid Association. Hypothyroidism. January 2020. Accessed January 2021. https://www.thyroid.org/patient-thyroid-information/ct-for-patients/january-2020/vol-13-issue-1-p-5-6/#:~:text=Current%20guidelines%20recommend%20that%20the,result%20in%20different%20health%20outcomes.