Thyroid hormone is the first hormone to have evolved in multicellular organisms when they left the iodine-rich atmosphere of the sea to live on land. Iodine was so important the thyroid evolved to make sure it was always available to cells. Endocrinologists have postulated that thyroid hormone controls all endocrine organs. Thyroid hormone is the first hormone to develop in the fetus. First, the thyroid, then the central nervous system, develop, with the tissues from the neural tube making the thyroid and then the brain, for which iodine is essential. Thyroid hormones not only grow our brain but control development and tissue growth.
There are thyroid hormone receptors in all cell membranes, all mitochondria, and all cell nuclei. It is thyroid hormone, specifically T3, the active thyroid hormone, that sparks the release of energy in all cells. T3 stimulates and de-accelerates metabolism—lipolysis and lipogenesis, protein synthesis, protein degradation, glucose consumption in cells (important in blood sugar regulation), and glucose production are controlled by T3.
All nutrients, including fats and proteins can be turned into ATP within each cell, using enzymes in the mitochondria where carbon and hydrogen are released. These are then combined with oxygen to make carbon dioxide and water create energy. T3 hormone assists these enzymes, enabling fat and proteins, sodium, potassium, and other chemicals, to pass into the cell membrane. Thyroid hormone also allows waste to move out of cells. It is T3 hormone that initiates the process of energy production in the mitochondria. The thyroid makes 80% t4, 16% t3, and 4% T2 and T1.
Mostly T3, but also to some extent T2, control the metabolism of lipids, proteins, and carbohydrates, primarily through the oxidation of fatty acids in most tissues. We now know that T2 is also involved in energy metabolism, especially in liver, heart, muscle, and brown adipose tissue. T3 also maintains cellular DNA, so it is involved in regeneration and immune function.
Since thyroid hormones activate all cells, all physiological functions suffer without enough active thyroid hormone. Symptoms as various as acid reflux, sleep apnea, arrhythmia and insomnia, depression, anxiety, low steroid hormones, gastrointestinal problems, joint pain, chest tightness, anemia, menstrual disorders, atherosclerosis, losing hair, fatigue, weight gain— the list goes on forever—are related to inadequate levels of thyroid hormone. Perhaps it isn’t a malfunction in the organ itself—in your intestines, in your lungs, in your brain, in your heart—but a lack of energy required for it to function properly.
The thyroid gland sits in the front of your neck and is innervated by sympathetic and parasympathetic nerves, one of which is the vagus nerve. The vagus nerve, also known as the wandering nerve, starts in the brain and travels from there to the tongue, thyroid, the heart (where it controls rhythm), the lungs, the stomach, and then to the intestines.
Not only are receptors for the active thyroid hormone T3 found in all cells, but because the superior laryngeal nerve, the branch of the vagus nerve that supplies the thyroid, contains both afferent and efferent fibers, inflammation in the thyroid can affect the function of the organs along vagus nerve. Inflammation in the various organs along this route can affect thyroid function. Inflamed thyroid tissue can also cause swelling and pain in the vertebra near the thyroid. Hence in some cases, neck pain is not due to degenerated bone tissue in the neck vertebra, but because surrounding tissue is swollen and impeding the proper movement of bones and ligaments.
Nutrition, intestinal function, and stress levels are the main causes of thyroid dysfunction. The production of thyroid hormone, as well as their transport around in the system, depends on adequate nutrition—a balance of raw materials for manufacturing, conversion, and transport.
Thyroid hormone molecules are made out of iodine and the amino acid tyrosine. The thyroid needs very particular amounts of different vitamins, minerals, and amino acids to manufacture hormones. But thyroid function also involves hormone conversion and hormone transport to target tissues. Without selenium, iron, and iodine, and other minerals, the three enzymes, deiodinase 1, deiodinase 2, and deiodinase 3, cannot be manufactured. These enzymes convert the inactive form of T4 into the active form of T3 and T2. There is also a T1, but not much is yet known about it’s function. Zinc and other minerals, both macro and trace, are essential for the synthesis of thyroid hormones in the thyroid itself and for the conversion of the inactive hormone thyroxine, T4 into its active form in peripheral tissues–in liver, kidney, heart, and muscle tissue. Specific proteins carry thyroid hormones to target tissues. Any digestive issues will disrupt this process.
Thyroid tissue itself suffers if the immune system mistakes the proteins on the enzymes that synthesize the nutrients to make hormones. If it mistakes them as enemies or antigens it will attack them, eventually destroying thyroid tissue. Autoimmune thyroid conditions are the most common of autoimmune disorders, and they are more prevalent in women. Autoimmunity can also be caused by inadequate nutrition.
Certain foods can trigger an autoimmune reaction because they cause inflammation. None of these foods are of animal origin, specifically soy and some vegetables, such as raw cabbage, cauliflower, and broccoli. Instead, animal-based nutrition will ensure you get all the raw materials you need to optimize thyroid function. Removing plant foods from your diet not only eliminates trigger foods, but also takes out foods that can interfere with the absorption of iron, B12, and other B vitamins, as well as goitrogens, that prevent iodine absorption, all essential to thyroid function. These nutrients are especially important during puberty, when the thyroid is busy forming sexual characteristics.
Chronic stress will make the thyroid suffer as well. The thyroid is a very sympathetic organ. It is stimulated by, and interacts with the sympathoadrenal system—the sympathetic nervous system and the adrenal medulla, whose activity is controlled by the hypothalamus and the brainstem. The thyroid is constantly responding to catecholamines—dopamine, norepinephrine, and epinephrine—synthesized by the adrenal glands. This means the thyroid reacts to temperature by warming you up or cooling you down. It also means that it responds to stress, be it physical or mental. Childhood trauma can damage thyroid function.
What the thyroid doesn’t need is carbohydrate. Starvation suppresses thyroid hormone conversion. This is because starvation, or any kind of stress, causes the thyroid to down-regulate conversion in peripheral tissues by the deiodinase enzymes. TSH and T4 hormone levels do not go down. The T3 levels go down. In starvation. and with isocaloric diets, T3 conversion is suppressed because T3 stimulates physiological processes. All biochemical and metabolic processes have to be curtailed with reduced nutrient intake, as there are fewer raw materials to go around. T3 conversion is suppressed to prevent the degradation and synthesis of the body’s own tissues. What T3 is available has to go to heart, kidney, and brain function. Growth and regeneration must be suspended. The studies that demonstrated reduced T3 conversion on low carbohydrate diets were done with low-calorie low-carbohydrate diets. In fact, studies that used high-fat diets with normal calorie intake showed no reduction in T3 levels.