When we think of thyroid function, many things come to mind like weight management, energy versus fatigue, lush thick hair or hair loss, and feeling too hot or cold or comfortable. Little thought is given to muscles and how thyroid hormone might affect their function. Recent findings help explain some of the delicate interplay with thyroid, mitochondria, and muscles that is essential to maintaining strong, healthy muscles.
Thyroid hormone affects the whole body. When it is out of balance, it creates a lot of symptoms. Cholesterol elevates, gallbladder sludge builds up, and blood sugar dysregulation, brain fog, and fatigue occur. Skeletal muscle needs activated thyroid hormone, too. If thyroid hormone is disrupted, then exercise intolerance, muscle cramps, muscle fatigue, weakness, and even soreness occurs. This can happen with both underactive and overactive thyroid concerns at any age.
There is another phenomenon that occurs with aging muscles and thyroid hormone. As you age, there is a decline in thyroid hormone production. This scenario is linked with loss of muscle mass and a change in quality of muscle tissues. This phenomenon is known as sarcopenia which means “loss of flesh”. With aging and sarcopenia, it gets harder and harder to maintain strength and endurance. Muscle mass declines and wastes away throughout the body with age.
The classic example of sarcopenia is seen in the appearance as loss of the gluts/buttocks and biceps muscle. What you had as a 20-something starts to sag and lose strength as the decades pass. The flight of stairs that you used to run up with ease now seems like a mountain to climb. Carrying a large bag of groceries now is exhausting compared to years prior.
Sarcopenia can happen with illness, but it is a significant concern affecting millions of older adults. A person can be thin or obese with sarcopenia. Obesity, diabetes, lack of physical activity, and insufficient nutrition are common reasons for loss of muscle mass and strength. Increased risk of falls and frailty are significant concerns due to sarcopenia.
There are some other muscle disorders linked with thyroid health, too.
Thyroid Hormone and Muscle
Thyroid hormone plays many roles in how skeletal muscle works and even how we build new muscle throughout life. As your body develops in infancy and childhood, thyroid hormone, especially T3 (triiodothyronine) is essential for the growth and development of muscles. It helps with the activity of different types of muscle fibers such as fast twitch and slow twitch muscles. These muscle types relate to sprinting (fast twitch) or endurance (slow twitch) muscles. Slow twitch/endurance fibers are also related with keeping a good posture.
T3 thyroid hormone helps muscles respond to insulin. It facilitates muscle usage of oxygen which is necessary for aerobic metabolism. T3 is also essential for making new mitochondria in muscles. With inadequate T3 thyroid hormone, mitochondria will not work nearly as well. Mitochondria in skeletal muscle depend upon T3 thyroid hormone. This interwoven relationship helps your body burn calories, produce heat and energy, assists with posture, movement, and function.
Consequences of Impaired Thyroid on Muscles
Researchers have found that the natural decline in muscle mass and strength or sarcopenia is linked to the age-related decline in T3 thyroid hormone activity. If T3 is limited in the muscles, then it becomes harder for muscles and mitochondria to work. Muscles work less efficiently with a greater tendency towards anaerobic metabolism. This leads to fatigue, cramping, soreness, impaired strength and exercise intolerance.
Muscle quality also declines. Blood sugar is also impacted as it is not as easily burned within skeletal muscle mitochondria as they need activated T3 to work. As a result, metabolism slows down, which causes muscle fibers to have more fat deposited in them. What you see is a loss of muscle mass and fatigue as the mitochondria and aerobic capacity declines.
Thyroid Hormone Activation in Muscles
About 80 percent of thyroid hormone produced by the thyroid gland is thyroxin (T4) thyroxine and about 20% triodothryonine (T3). T4 must be activated or converted into T3 for healthy metabolism to occur. Special compounds that help this activation process are the selenoproteins D1, D2, and D3 or iodothyronine deiodinases type enzymes. These selenium-protein compounds are critical for thyroid hormone activation.
Of the three main selenoproteins, D2 is the most critical for adequate T3 thyroid hormone levels in skeletal muscles. D2 also helps energize T3 in the brain and brown fat which is essential for fat burning and making heat and energy. Adequate selenium and protein in the diet are critical for this daily need. In addition, zinc and vitamin D are required for usage of thyroid hormone within cells.
Scientists aren’t sure of everything that happens with age-related decline with thyroid hormone levels and loss of muscle mass and strength. They do know, however, that physical activity helps your body with these concerns in many ways. Exercise increases skeletal muscle D2 selenoprotein activity, which helps build muscle. Exercise also stimulates the production and activation of mitochondria, which further helps T3 in muscles and aerobic capacity. They also know that individuals who support their thyroid hormone levels and activation of T4 to T3 have muscle tissues that feel better.
Other ways to help muscles and thyroid includes support of cell membranes, mitochondria, and the connections between the brain, adrenal glands, and stress. Cell membranes and receptor sites need good fats like omega-3 oils, choline and phosphatidylserine in order for hormones and other signals to pass in and out of cells. The adrenal glands and mitochondria may need support to help the grumpy and exhausted feelings coming from a stressed neuroendocrine system. Adaptogenic herbs like holy basil, Rhodiola rosea, and ashwagandha provide support and balance to the thyroid, adrenals, and nervous system in managing stress. Coenzyme Q10, B vitamins, PQQ, and acetyl-l-carnitine provide fuel for mitochondria.
Aging is inevitable. But how well we age depends on many things that we have control over. In the case of muscles and thyroid hormone, the saying ‘use it or lose it’ applies. It's never too late to help your muscles and thyroid hormone healthfully age.