As a physical therapist, the skeletal muscle is my favorite organ. It is not only a locomotor apparatus as we have all come to know but it has endocrine action with ability to secret hundreds of peptide molecules called myokines that act on distant organs for overall health of the body. For more important reasons beyond being a movement specialist type like me, I dare say that the skeletal muscle ought to be your favorite organ as well. Apart from sleeping, infectious state or physical trauma, skeletal muscle is a principal organ for basic human activities such as foraging, farming or fight/flight response in case of life-threatening events. Simply stated, the skeletal muscle is the bedrock of quality-of-life allowing us to perform voluntary and spontaneous movements in a staggering under-appreciated fashion until we are hit with trauma or sickness!
The question is: what has skeletal muscle got to do with thyroid hormones? All organs have different functions and are directly connected either by blood vessels or by the so-called “cross-talk” through hormones without direct connections. Anyway, the thyroid gland, located in front of the neck secretes two main hormones called triiodothyronine (T3) and thyroxine (T4). These hormones are found in the blood stream and practically inside every cell in the body where they have major influence on your energy levels, internal temperature, weight, skin, breathing, hair, growth and much more. Hormones T3 and T4 act inside every cell to produce energy using slow but efficient aerobic respiration that requires oxygen to burn nutrients. It should be noted that T3 is more potent than T4 and therefore T4 is often converted to T3 to increase the rate of cellular metabolism.
However, as in the case of chicken and egg situation, there have been a lot of controversies in medical literature about whether sluggish thyroid (i.e., low T3 and T4) causes weight gain or weight gain causes underactive thyroid. Unfortunately, the role of skeletal muscle as a moderating influence between energy-gulping selfish brain and immune systems is largely unknown in medicine. For better understanding, every system in the body has a limited energy allocated to it and the total allocation for each system makes up for daily energy expenditure which is constant for all humans throughout life. Though speculative, it has been noted that if the body were to simultaneously “fund” the energy needs of the costly selfish brain and selfish immune system, the heart rate would be about 180 beats per minute and the blood pressure would be chronically sustained at about 160/120 at rest, which would certainly damage the brain and possibly rip out the heart upon minimal physical activity!
To prevent energy conflicts between the brain and the immune system, regular physical activity during the daytime allows the brain to keep its needed energy allocation while hunting, foraging, or physically fighting the enemy, after all, none of this can be done without the smart brain. Through the contracting skeletal muscle, physical activity allows the immune cells to cooperatively stay in low energy anti-inflammatory mode that protects the moving and working individuals against microbes and heal potential skin cuts without overwhelming immunological response. While the brain is considered smart, the immune system is primitive but highly robust. Immune system therefore responds to not only antigens but to external factors such as pollutants, toxins and even excessive food nutrients.
Therefore, in a hyper-stressed situation typical of sedentary lifestyle and chronic availability of energy dense foods, the ever-expanding fat mass and selfish immune system release a peptide molecule (interleukin 6) to reduce glucose uptake by the liver and skeletal muscle. This peptide also activates an enzyme called deiodinase 3 located in all cells to simultaneously block T3, the hormone responsible for burning nutrients using oxygen and convert T4 to reverse T3 (rT3). Reverse T3 prompts immune cells to switch metabolism from aerobic to anaerobic respiration by expending massive amounts of glucose through fast but inefficient energy production without the need for oxygen, making available multiple intermediate metabolites to grow immune cells. In brief, the selfish immune system hijacks the control of thyroid gland by reducing metabolic rate of all systems and commandeer the glucose resources even at the expense of the selfish smart brain. This causes the brain to increase the release of a hormone called thyroid stimulating hormone (TSH) to desperately pump up T3 and T4 hormones. The high TSH and low T3 and T4 is called hypothyroidism.
Beside physical inactivity, it must be noted that there are real medical conditions that may be predisposed to low thyroid. That said, almost all non-communicable diseases, including overweight/obesity, are caused by energy conflicts between the brain and immune system leading to years of low grade “cold” and painless inflammatory conditions showing up as diseases such as diabetes, high blood pressure, heart diseases and even cancers. As common practice in modern medicine, levothyroxine is the preferred choice of medicine to normalize thyroid hormones. However, studies have shown limited evidence that thyroid hormone treatment leads to weight loss, and according to Dr. Kitahara, an epidemiologist, if you are obese with an elevated TSH, weight loss may be a better course of action if testing does not turn up any underlying thyroid disorders.
There’s the rub; we are smart to know that hypothyroidism is caused by low thyroid hormones, but we never walk our way back to ask how? To lose weight and restore thyroid hormone levels would require the burden of fasting and exercise but who wants to do that? Of course, there is levothyroxine, a manufactured form of T4 to save the situation. Here is the fact, levothyroxine is on the World Health Organization’s List of Essential Medicines and according to Clincalc Drug Usage Statistics, behind atorvastatin, a cholesterol control drug which is also largely unnecessary with lifestyle intervention, levothyroxine was the second most commonly prescribed medication in the United States with about 106 million prescriptions in 2018.
The irony is that multiple studies have shown that regular physical activity or fasting and better still the combination of both (with your physician please) increases metabolic rate and causes weight loss. The big question is: who out there is promoting a healthy lifestyle of fasting and physical activity that costs zero dollars?
Mukaila Kareem, a doctor of physiotherapy and physical activity advocate, writes from the U.S.A and can be reached through email@example.com