Thyroid Hormone – The Metabolic Hormone

Dear BLOG readers, dear PEAK customers,

In addition to the hormones and neurotransmitters already discussed on the BLOG, today I’d like to add another hormone that is EXTREMELY relevant to sports: the thyroid hormone.

Thyroid hormone is a messenger substance essential for the entire body and plays a role in an incredible variety of bodily processes. Without thyroid hormone, we cannot survive. A great many people are affected by thyroid dysfunction and must undergo treatment to correct an excess or deficiency. In sports, thyroid hormones have also gained notoriety as performance-enhancing drugs.

In Part 1, I’d like to introduce the thyroid gland and explain the importance of iodine for thyroid function. I’d also like to explain how a goiter develops and what complications can result from it.

In Part 2, I’ll address the classic thyroid disorders and provide insight into exactly how thyroid hormone production affects the development of obesity. Finally, I’d like to explain what needs to be considered regarding exercise when dealing with a thyroid disorder and how exogenous thyroid hormones are used as performance-enhancing drugs.

The Thyroid Gland

General

The thyroid gland is a very small but vital organ. It consists of two lobes connected by a bridge of tissue. It is roughly shaped like a butterfly. The thyroid gland is located below the larynx, in front of the trachea. In adults, it weighs between 10 and 20 grams.

Illustration: Location of the thyroid gland

Regulation

The brain controls the release of thyroid hormone; more specifically, this is done by the pituitary gland and the hypothalamus. The pituitary gland detects the amount of thyroid hormone present in the blood and, depending on the concentration, activates or deactivates the thyroid gland by secreting its messenger substance. (Negative feedback). The messenger substance required for this, produced by the pituitary gland, is called TSH (thyroid-stimulating hormone). The pituitary gland, in turn, is controlled by the hypothalamus via the hormone TRH (thyrotropin-releasing hormone).

Stimulation of the thyroid gland by TSH triggers the production of the following hormones:

• Triiodothyronine, liothyronine, T3
• Tetrajodthyronin, thyroxine, T4 in the thyrocytes, as well as
• calcitonin in the parafollicular cells

Thyrocytes are the hormone-producing and follicle-forming cells of the thyroid gland.

The hormones produced are synthesized from protein and iodine, stored in the thyroid gland, and released into the bloodstream as needed.

Illustration: The thyroid gland’s regulatory loop

Functions and Effects of the Thyroid Gland

The thyroid gland influences the development and function of many important systems in the body, such as the brain, the central nervous system, and the skeleton.

The thyroid gland influences macronutrient metabolism as well as mineral balance, water balance, oxygen consumption, and gastrointestinal functions (stomach and intestines).

Among other things, the thyroid gland regulates the secretion of gastrin (a tissue hormone of the gastrointestinal tract), stomach acid, and insulin, as well as enzyme production in the pancreas.

Ultimately, the thyroid gland is crucial for mental development and mental and physical performance.

The thyroid gland has a direct (unmediated) influence on the pituitary gland, the diencephalon, the heart, the kidneys, the intestines, the ears, and the eyes, as well as on blood formation.

Indirectly (through an intermediate pathway), it influences the parathyroid glands, the adrenal glands, and the gonads.

Illustration: Effects of Thyroid Hormones

Normal Values

Below is a list of normal values for adults related to the thyroid gland

Illustration: Normal Values for Thyroid Hormones

Iodine and the Thyroid Gland

Iodine

Iodine is an essential trace element, meaning it must be obtained through the diet. The body’s stores are limited because iodine is excreted through the kidneys and intestines. Only a very small portion can be reused. No other substance can perform the functions that iodine does in the body.

Iodine is essential!

In the human body, iodine is primarily needed by the thyroid gland to produce thyroid hormones. The thyroid gland can absorb iodine very effectively from the intestines, through the skin, and from the air we breathe.

Function

The thyroid gland requires iodine as a building block for the production of thyroid hormones. The two thyroid hormones, T4 and T3, contain four and three iodine atoms per molecule, respectively.

For this reason, approximately 200 micrograms of iodine should be consumed daily. Without sufficient iodine, the thyroid gland cannot function properly. Iodine requirements are higher during certain life stages and at certain ages. These include pregnancy, breastfeeding, and competitive sports. In breastfeeding mothers, iodine is absorbed into the mammary glands and passed on to the child through breast milk.

Illustration: Iodine Requirements

Intake Status

In Germany, most people tend to have an insufficient iodine intake. The thyroid gland reacts to this by enlarging to form a sort of sponge that strives to absorb as much of the ingested iodine as possible. This enlargement is called a goiter. If left untreated, a goiter often leads to the development of so-called cold or hot nodules.

Supporting Iodine Intake

Even today, most Germans consume less than 100–150 mcg of iodine per day. The WHO has identified this as the critical threshold. The problem with iodine intake is that most common foods contain only trace amounts of it.

TIPS for Adequate Iodine Intake

• Eat ocean fish (salmon, plaice, haddock, etc.) twice a week
• Use iodized salt at home
• Consume dairy products daily (iodine is added to animal feed)

Table: Iodine content of selected foods

Differences Among Iodized Salts

Pregnancy and Iodine Tablets

Pregnant women have an increased need for iodine, which usually cannot be met through diet alone. In addition to the mother’s own increased need, the baby’s thyroid gland begins to function starting in the second trimester and must also be supplied with iodine through the mother. This situation continues during breastfeeding via breast milk.

Differences in the Development of Iodine Deficiency

Poor Iodine Utilization

Due to genetic factors, iodine absorption can vary within families—from better to poorer—which affects iodine status.

Gender

Women are more likely to develop a goiter or thyroid dysfunction because they have higher levels of T3 and T4 hormones bound to transport proteins (inactive forms). Their iodine requirements are therefore higher than those of men. This function likely serves to ensure the availability of iodine during pregnancy.

Other Factors

Iodine requirements are also influenced by height, weight, the amount of transport proteins present, work intensity, physical activity, and climatic conditions.

Tobacco smoke also contains substances that interfere with iodine absorption. Smokers are twice as likely to develop goiter as nonsmokers.

Iodine Deficiency in Sports

Exercise accelerates metabolism and calorie expenditure and promotes the development of more muscle mass. These changes increase the body’s need for thyroid hormones and, consequently, for iodine. In addition, iodine is lost through sweat, which is particularly significant in endurance sports.

There is an increased need for iodine in sports!

Iodine Deficiency and Vegetarian Diets

Vegetarians largely avoid all significant sources of iodine. Vegans, who also avoid dairy products, are particularly at risk. Furthermore, consuming certain vegetarian foods (cabbage, legumes, seeds, and nuts) can inhibit iodine absorption. Vegetarian foods are also lacking in selenium and iron. These two trace elements also influence thyroid hormone metabolism. Selenium also protects the thyroid from damage caused by “free radicals.” Excessive consumption of seaweed and kelp as part of “alternative” diets can lead to an excessive intake of iodine.

Goiter and Iodine Deficiency

As we’ve already read above, a goiter results from an enlargement of the thyroid gland caused by iodine deficiency. Part of this tissue often develops into nodules. These nodules can form even in a thyroid gland of normal size, but this occurs more frequently in an enlarged thyroid gland.

A goiter isn’t always visible. When it’s not visible, it’s called a “hidden goiter.” You can recognize it by a feeling of pressure or tightness in the neck. Often, however, there are no symptoms at first.

A goiter is more likely to develop cold or hot nodules!

Treatment

A goiter is treated with either iodine tablets or thyroid hormone tablets, either alone or in combination. A reduction in thyroid size can often be achieved after 6–12 months of therapy. Afterward, maintenance therapy is usually required. Very large goiters or goiters in very elderly individuals often need to be surgically removed. Radioiodine therapy can also be used to reduce the size of a goiter (thyroid reduction).

Thyroid Nodules

Hot Nodules

These are tissue changes in the thyroid gland. They absorb increased amounts of iodine and produce thyroid hormones uncontrollably. The nodules are no longer controlled by the pituitary gland (autonomous nodules) and thus lead to hyperthyroidism over the long term. They are active regardless of the body’s needs and are therefore the cause of half of all cases of hyperthyroidism.

Hot nodules are benign in the vast majority of cases.

Cold Nodules

Cold nodules are inactive. They do not absorb iodine and do not cause hyperthyroidism. They are often small calcifications, old scarred tissue, or benign tumors. Only in rare cases might a cold nodule conceal a malignant tumor. Surgery is usually required to remove it.

Symptoms and Signs

As the nodules grow, they can cause mechanical symptoms such as difficulty swallowing or a feeling of pressure. Additionally, other symptoms of hyperthyroidism may occur if the nodule is a hot nodule.

Diagnosis

A blood test can be used to diagnose thyroid function. If the thyroid gland produces too much thyroid hormone, the pituitary gland produces less or no TSH. If the thyroid gland is underactive, TSH levels rise.

In the case of a hot nodule, the nodule no longer responds to regulatory signals. The nodular tissue does not respond, while the normal tissue remains regulated. Once the nodular tissue has gained the upper hand, the autonomous nodular areas produce more thyroid hormone than the entire thyroid gland would normally produce.

In the case of a cold nodule, there is no change in thyroid hormone production; consequently, it cannot be detected through a blood test. In such cases, regular physical examinations are recommended starting at a certain age.

Antibody testing is not relevant for diagnosis. However, a diagnosis based on calcitonin levels is possible.

Calcitonin

Calcitonin is the third thyroid hormone. It has important effects on calcium metabolism by inhibiting pathologically increased bone resorption. In some cases, it has a pain-relieving effect. As a medication, it is mainly used nasally to treat bone diseases associated with bone resorption (Paget’s disease or postmenopausal osteoporosis).

Summary

The thyroid gland is a small but extremely important organ in our body. Through the production of thyroid hormones, it influences countless bodily processes and is regulated via feedback from the brain. Iodine, among other things, is required for the production of thyroid hormones; in Germany, there is generally a deficiency of this essential trace element. Long-term deficiencies can lead to the development of a goiter, which generally refers to an enlargement of the thyroid gland. Untreated goiters often give rise to so-called “hot” or “cold” nodules. A cold nodule is an inactive growth of tissue. A hot nodule, on the other hand, is an active, autonomous accumulation of tissue that absorbs increased amounts of iodine and produces thyroid hormones uncontrollably. Hot nodules can be a cause of hyperthyroidism.

In Part 2, I’ll discuss thyroid dysfunction, explore the connection between thyroid hormones and obesity, provide some information on managing thyroid dysfunction in sports, and shed some light on the topic of “the use of thyroid hormones as performance-enhancing drugs.”

I hope that you, dear readers, are looking forward to Part 2 as much as I am.

Best regards,

Yours,

Holger Gugg

www.body-coaches.de