Are you always cold? Does it seem you can never get warm, even when you are bundled up? Do your fingers and toes freeze even in mild temperatures? If so, you are struggling with cold intolerance a clear sign of compromised cellular hypothyroidism.
Cold intolerance is one of the most common complaints reported by my patients diagnosed with hypothyroidism and Hashimoto’s disease. While many people realize that thyroid hormone plays a critical role in energy and heat production, what they don’t understand is:
- how thyroid hormone regulates the production
- why hypothyroidism causes cold intolerance
- why thyroid hormone replacement therapy may not improve their cold intolerance
There are two primary ways that heat is generated in the body, and thyroid hormone plays a critical role in both of them. Heat is generated as a byproduct of metabolism in the body. Just like heat is generated by your car engine, or by your refrigerator as a normal by-product of their normal function so is heat produced as a natural by-product of basal metabolism.
When you are in an environment with moderate ambient temperature, the basic or basal metabolic actions of the body generate enough heat to keep your body at approximately 98.6 degrees. When you are exposed a cold environment, the body kicks in a second mechanism to generate heat and restore your core temperature. Thyroid hormone plays a critical role in both mechanisms.
Thermogenesis
Thermogenesis is the term for the generation of heat. Within the body there are two forms. Obligatory thermogenesis which is the production of heat generated as the natural by-product of basal metabolic functions of the body like pumping blood, making energy, making proteins, and performing functions of digestion. The second mechanism used by the body to generate heat is called facultative thermogenesis and is the adaptive process to generate heat when obligatory thermogenesis isn’t sufficient to keep the body in its optimal thermogenic range. When you go outside in 30-degree weather, it’s the facultative thermogenesis that warms you up.
Facultative (aka adaptive) thermogenesis occurs by two means voluntary actions and involuntary actions. When cold sensors on your skin sense cold, signals are sent via nerves to the central nervous system to kick adaptive thermogenesis into gear. Voluntary actions kick in like putting on more clothes and curling up with a blanket. Involuntary actions are also activated.
Involuntary actions include; vasoconstriction of blood vessels to prevent heat loss through the skin, shivering to generate heat through muscle contraction, and lastly the coordinated action of thyroid physiology and the sympathetic nervous system to activate the brown adipose tissue (a form of body fat) to burn off fat stores to generate heat.
Both facultative and adaptive thermogenesis work flawlessly in those with optimal thyroid physiology. For those with compromised thyroid physiology, the thermogenic processes are often compromised leaving you feeling cold even in mild conditions.
Cold intolerance is a classic sign of cellular hypothyroidism. Cellular hypothyroidism, a term many are unfamiliar with, is an insufficient amount of thyroid hormone is your cells. Most people are familiar with terms like primary hypothyroidism which is a condition where the thyroid gland is not making sufficient thyroid hormone, the most common cause being Hashimoto’s Thyroiditis.
In primary hypothyroidism the thyroid gland is producing insufficient thyroid hormone, which can impact nearly all the tissues and cells of the body. Without sufficient thyroid hormone being made by the gland there is insufficient thyroid hormone in your tissues to support optimal basal metabolism. If there is less, then optimal thyroid hormone to drive basal metabolism of the body there is less heat driven by obligatory thermogenesis causing your core body temperature to be lower. Even a drop of a few degrees in core body temperature will cause you to feel cold.
Your body should induce adaptive thermogenesis to warm you up, and it does make an attempt to do so. Both the voluntary and involuntary systems kick in. The sympathetic nervous system is ramped up to produce norepinephrine (a neurotransmitter) to activate your brown adipose tissue to start metabolizing fat stores to generate heat. TSH levels rise to drive up production of the thyroid gland. But, due to reduced levels of thyroid hormone (T4 and T3) produced by the gland and reduced thyroid hormone getting inside your cells, the effort of the sympathetic nervous system to generate additional heat fails.
But why are you still cold when you are taking thyroid hormone replacement therapy?
In theory, once you are put on thyroid hormone replacement therapy and your TSH returns to normal range you are said to be in a state of euthyroidism (normal thyroid physiology). In a medically supported euthyroid state, it is thought by many that all cells and tissues will have their normal thyroid physiology restored. In theory in sounds good. But in reality, that is often not the case. Why? The complete answers are a bit complex, so I will simply the complex science for this post.
When you have overt glandular hypothyroidism, all tissues have reduced levels of thyroid hormone. When you take thyroid hormone replacement therapy your lab values of TSH and T4 values can normalize. But what we now understand is that normal levels of TSH do not necessarily represent optimal levels of thyroid hormone in all tissues, or optimal thyroid physiology within all tissues. Thyroid hormone replacement therapy can result in restoration of thyroid hormone within the Hypothalamus (an area in the brain), long before levels of thyroid hormone levels are optimized within the heat generating tissues of the body. If your hypothyroid gland is optimized, signified by normal TSH levels, but peripheral tissue levels of thyroid hormone are insufficient to support optimal adaptive thermogenesis, you will be chronically cold.
A second reason you may be cold despite thyroid hormone replacement therapy is that the thyroid hormone you are taking must get transported from the blood and into the cells of the heat generating tissues. If something is inhibiting transport of T4 into your cells, you will have cold intolerance despite normal TSH and T4.
Once inside your cells, especially the heat producing brown adipose tissue, T4 must be converted into T3. T4 can be converted into T3 (by an enzyme called Deiodinase 2) and support heat generation or be converted into reverse T3 (by an enzyme called Deiodinase 3) which does not support heat generation. Only T3 not reverse T3 (rT3) drives the actions of thermogenesis. It is now understood that cells determine the action and outcome of thyroid hormone. The thyroid gland provides bulk thyroid hormone to the blood, but individual tissues control what happens to thyroid hormone once it enters the cells of the tissues.
Cold Intolerance is a sign of insufficient thyroid hormone, cellular hypothyroidism, in your heat generating tissues.
Your questions at this point may be:
- How do I determine if I have cellular hypothyroidism?
- What is causing cellular hypothyroidism?
- How do I fix my cellular hypothyroidism?
How can you determine if you have cellular hypothyroidism?
Identifying cellular hypothyroidism is not always straightforward. There is however a test available to measure your level of reverse T3 (rT3). If your rT3 is elevated above lab range, and you have chronic hypothyroid symptoms like cold intolerance, the elevated rT3 is a likely a good indicator that cellular hypothyroidism is present. In my functional medicine practice, I feel a rT3 value greater than 18 is less then optimal and a sign of cellular hypothyroidism.
I also like to look at the ratios of T3/rT3 and fT3/rT3 when rT3 is within normal range. If the ratios are less than optimal 10 and .20 respectively, and a person has chronic hypothyroid symptoms, I assume they have cellular hypothyroidism.
The challenge for many is that rT3, T3, and fT3 are rarely run in allopathic medicine. You will likely need to find a functional medicine practitioner who focuses on thyroid physiology to have these tests run and interpret them correctly.
What causes cellular hypothyroidism?
What is causing cellular hypothyroidism especially in your brown adipose tissue and causing your cold intolerance? The primary factor causing increased levels of rT3 and cellular hypothyroidism is inflammation. Inflammation driven by infections, toxins, trauma, tissue damage, and oxidative stress can increase the levels of rT3 and lower the levels of cellular T3, inhibiting optimal thermogenesis and cause you to be chronically cold.
How to fix cellular hypothyroidism
This is where functional medicine shines. In functional medicine the goal is to identify the cause or causes of cellular stress and inflammation. By identify the cause or causes and removing or reducing the causes as much as possible, you can restore cellular thyroid physiology, restore thermogenesis, and eliminate your cold intolerance.
What if you are chronically cold but you have been told your TSH is normal and you don’t have hypothyroidism?
I know many of you reading this may fall into this category. You likely have symptoms of hypothyroidism despite a normal TSH. In this situation, you may still have normal thyroid gland function and thyroid hormone production. The problem is not with your gland but within your cells and tissues. You may have chronic inflammation or other factors that are preventing thyroid hormone from getting into your cells and being converted for optimal metabolism. You may have chronic inflammation that is suppressing TSH, hiding a hypothyroid condition.
If you have cellular hypothyroidism caused by chronic inflammation your basal metabolism and heat generation will be reduced causing you to be cold even with your two sweaters and wool socks. Your adaptive thermogenic response will try to work but without sufficient T3 in your cells your brown adipose tissue just can’t make sufficient heat to bring your temperature up, especially when you step out into the cold.
For those looking for help with chronic hypothyroid symptoms and cold intolerance, schedule a complimentary discovery call at www.rejuvagencenter.com
References:
- ‘Iwen, K., Oelkrug, R., & Brabant, G. (2018). Effects of thyroid hormones on thermogenesis and energy partitioning, Journal of Molecular Endocrinology, 60(3), R157-R170. Retrieved Jan 2, 2020, from https://jme.bioscientifica.com/view/journals/jme/60/3/JME-17-0319.xml
- Cioffi F, Gentile A, Silvestri E, Goglia F, Lombardi A. Effect of Iodothyronines on Thermogenesis: Focus on Brown Adipose Tissue. Front Endocrinol (Lausanne). 2018;9:254. Published 2018 May 23. doi:10.3389/fendo.2018.00254
- Zhang Z, Boelen A, Kalsbeek A, Fliers E. TRH Neurons and Thyroid Hormone Coordinate the Hypothalamic Response to Cold. Eur Thyroid J. 2018;7(6):279–288. doi:10.1159/000493976
- Carpentier AC, Blondin DP, Virtanen KA, Richard D, Haman F, Turcotte ÉE. Brown Adipose Tissue Energy Metabolism in Humans. Front Endocrinol (Lausanne). 2018;9:447. Published 2018 Aug 7. doi:10.3389/fendo.2018.00447
- Alcalá M, Calderon-Dominguez M, Serra D, Herrero L, Viana M. Mechanisms of Impaired Brown Adipose Tissue Recruitment in Obesity. Front Physiol. 2019;10:94. Published 2019 Feb 13. doi:10.3389/fphys.2019.00094
