The thyroid gland and metabolism: a silent battle that shapes your body

The Hidden Metabolic Secret Behind an Ideal Weight

Introduction

The thyroid gland is a pivotal component of the endocrine system. Its hormones (thyroxine T4 and triiodothyronine T3) control the regulation of basal metabolic rate, energy balance, and the activity of most body systems. Weight is one of the most prominent indicators affected by thyroid function, as insufficient activity leads to a slowdown in metabolic processes and increased accumulation of fat and fluids, while overactivity is associated with accelerated metabolism and unexplained weight loss. This close relationship makes studying thyroid function a fundamental necessity for understanding the mechanisms of weight control and diagnosing the causes of unexplained obesity or thinness. Furthermore, linking these indicators to laboratory test results for thyroid function (TSH, T3, T4) represents a cornerstone in the clinical evaluation of weight disorders. Therefore, a review of this relationship from a physiological and clinical perspective contributes to improving diagnosis and developing more accurate and effective treatment strategies.

What Is the Thyroid Gland?

It is a small, butterfly-shaped gland located in the middle of the lower part of the neck. Its main function is to regulate the body's metabolism—the rate at which cells perform essential duties to keep the body alive. To this end, the gland secretes the hormones T3 and T4, which determine the amount of energy the body's cells must use. A healthy thyroid gland maintains the secretion of the appropriate amount of hormones the body needs to maintain a proper metabolic rate. When hormones are depleted, the thyroid gland secretes replacement quantities. The pituitary gland, located at the center of the skull, controls the amount of thyroid hormone secretion and its levels in the blood. When the pituitary gland detects a deficiency or excess in thyroid hormone levels, it adjusts the level of its own hormone (TSH) and sends it to the thyroid gland to tell it what to do.

Source: Thyroid Disease: Symptoms, Causes, and Diagnosis | Hypothyroidism

The Pituitary Gland and Its Relationship with the Thyroid

The pituitary gland is a very small gland located at the base of the brain inside a bony cavity called the sella turcica. Despite its small size, it is known as the "master gland" because it controls the function of many other glands in the body. One of its most important roles is its relationship with the thyroid gland, as it secretes a hormone called Thyroid-Stimulating Hormone (TSH). This hormone sends a direct signal to the thyroid gland to stimulate it to produce T4 (thyroxine) and T3 (triiodothyronine), which are the hormones responsible for regulating metabolism and energy in the body. The relationship between the pituitary and thyroid works according to a system known as negative feedback. When T3 and T4 hormone levels rise in the blood, TSH secretion decreases to maintain balance. If they decrease, the pituitary gland increases TSH secretion to push the thyroid gland to work harder. This system helps doctors interpret blood tests. If TSH is high and T4 is low, this indicates a deficiency in the thyroid gland itself (primary hypothyroidism). If TSH is low and T4 is low, this indicates a problem in the pituitary or hypothalamus (secondary hypothyroidism). In the case of an overactive thyroid, we usually find low TSH with high T3 and T4, while high TSH with high T4/T3 indicates a TSH-secreting pituitary tumor.

Types of Thyroid Diseases

Thyroid diseases are mainly divided into two basic types: Hypothyroidism and Hyperthyroidism. Each has several medical conditions that may lead to it. The most prominent conditions causing hypothyroidism include:

• Hashimoto's disease: a chronic autoimmune disease that is the most common cause of hypothyroidism in countries where iodized salt and iodine-rich foods are available.

• Iodine deficiency: since the thyroid gland needs iodine to produce hormones, its deficiency in the diet leads to hypothyroidism. It is the most common cause in countries where iodized salt is not available and is often associated with goiter.

• Congenital hypothyroidism: some children may be born without a thyroid gland or with an underdeveloped or ineffective gland. Its incidence is between one in 2000–4000 births.

As for the conditions causing hyperthyroidism, they include:

• Graves' disease: a chronic autoimmune disease that is the most common cause of hyperthyroidism.

• Thyroid nodules: small lumps or tumors in the thyroid gland that may be hormonally active and lead to hyperthyroidism.

• Iodine excess: when iodine in the body increases, either through the diet or some medications such as amiodarone (a cardiac drug), the gland secretes excessive amounts of hormones.

• There are also conditions that may cause both hypothyroidism and hyperthyroidism at different times, including:

  • Thyroiditis: a temporary or chronic inflammation that may start with temporary hyperthyroidism and then end with temporary or permanent hypothyroidism.

  • Postpartum thyroiditis: a relatively rare condition that affects about 5% of women during the first year after pregnancy and is characterized by a hyperthyroid phase followed by hypothyroidism, which is often temporary.

  Source: Thyroid Disease: What It Is, Causes, Symptoms & Treatment

  Prevalence of Thyroid Disorders

  Thyroid damage is one of the most prominent endocrine disorders globally:

  • Hypothyroidism affects between 3% and 10% of adults and is more apparent in women and the elderly.

  • Graves' disease, as a major cause of hyperthyroidism, appears at a rate of approximately 0.5% in men and 3% in women and is the most common cause of hyperthyroidism.

  • From a nutritional perspective, nearly one-third of the world's population lives in iodine-deficient areas, and in severely deficient areas, the incidence of goiter can reach 80%.

  Source: Wikipedia

• Causes of Thyroid Disorders

  Thyroid disorders, whether hypothyroidism or hyperthyroidism, have a variety of causes:

  • Autoimmune diseases: such as Hashimoto's disease, which causes hypothyroidism, and Graves' disease, which leads to hyperthyroidism.

  • Thyroiditis: inflammation may initially cause temporary hyperthyroidism followed by a gradual decrease in function.

  • Iodine deficiency or excess: iodine deficiency hinders hormone production and leads to hypothyroidism, while excess, sometimes as a result of taking medications like amiodarone, may cause hyperthyroidism.

  • Congenital: some children are born with an inactive or underdeveloped gland, which causes hypothyroidism from birth.

  Source: Thyroid Disease: What It Is, Causes, Symptoms & Treatment

  Main Symptoms of Hypothyroidism

  Hypothyroidism occurs when T3 and T4 hormone production decreases, leading to a slowdown in metabolic processes within the body. The most common symptoms are as follows:

  • Feeling tired and chronically fatigued due to the slowdown of vital processes.

  • Weight gain despite no change in diet, due to slow calorie burning.

  • Cold extremities and cold intolerance, dry and rough skin, and brittle hair loss.

  • Swelling of the face and puffiness around the eyes.

  • Chronic constipation due to slow digestive tract movement, a slow heart rate, and poor concentration.

  • In women, menstrual cycle disturbances or delayed pregnancy may occur.

• • Main Symptoms of Hyperthyroidism

  • In this case, the gland secretes excessive amounts of hormones, which leads to accelerated metabolism in the body. The most prominent symptoms are:

    • Significant weight loss despite increased appetite.

    • Heart palpitations and a rapid heart rate with a possibility of atrial fibrillation.

    • Feeling nervous and excessively anxious with insomnia and difficulty sleeping.

    • Excessive sweating and heat intolerance.

    • Hand tremors and muscle weakness, especially in the thigh muscles, and diarrhea or increased bowel movement.

    • Eye swelling, especially in Graves' disease.

    • In women, menstrual cycle disturbances may occur.

    Source: Hypothyroidism (underactive thyroid) - Symptoms and causes - Mayo Clinic and Hyperthyroidism (Overactive Thyroid): Symptoms & Treatment

  • The Thyroid Gland and Metabolism

    The thyroid gland plays a fundamental role in regulating metabolism by secreting the hormones thyroxine (T4) and triiodothyronine (T3), which act as a primary regulator of the body's basal metabolic rate. In a state of natural balance, they maintain the stability of energy production and consumption, ensuring cells and tissues are nourished with the necessary efficiency. In the case of an overactive thyroid, the increased hormone secretion accelerates energy burning, causing rapid weight loss, an increase in appetite, and a rapid heart rate. In contrast, hypothyroidism leads to a slowdown in metabolic processes due to a decrease in hormones, which is reflected in weight gain, a constant feeling of fatigue and coldness, and poor concentration. Therefore, any dysfunction in thyroid function has a direct impact on body weight, energy levels, and the health of vital organs.

  • Weight Gain, Loss, and Their Relationship with Thyroid Disorders

    The thyroid gland plays a fundamental role in regulating weight through its direct control over the metabolic rate, or what is known as the burning process. In the case of hypothyroidism, hormone secretion (T3 and T4) decreases, leading to a slowdown in metabolism, fat accumulation, and weight gain despite a stable diet, in addition to other symptoms such as fatigue and fluid retention. Conversely, hyperthyroidism leads to an unnaturally accelerated metabolic rate, which causes rapid and unexplained weight loss, even with an increased appetite, and is usually associated with accompanying symptoms such as a rapid heart rate, nervousness, and excessive sweating. Therefore, unexplained changes in weight are an important indicator of thyroid disorders, which necessitates a precise medical evaluation of its functions.

  • Insulin Resistance and Its Relationship with Thyroid Disorders

    The thyroid gland plays a pivotal role in regulating the metabolism of carbohydrates and fats, which explains its close association with the occurrence of insulin resistance. In the case of hypothyroidism, the metabolic rate decreases and visceral fat accumulation increases, which weakens the cells' sensitivity to insulin and leads to insulin resistance, raising the risk of developing metabolic syndrome and Type 2 diabetes. In the case of hyperthyroidism, the increase in thyroid hormones (T3 and T4) leads to an acceleration of glucose consumption and an increase in glucose production from the liver, which may cause high blood sugar levels and disturb insulin balance. Therefore, both types of thyroid disorders may directly or indirectly contribute to the development of insulin resistance, which necessitates careful monitoring of blood sugar levels and thyroid function together to achieve an optimal healthy balance.

  • Methods for Diagnosing Thyroid Disorders

    Diagnosis relies on a combination of examination and laboratory tests, including:

    • TSH test: The most sensitive test, as a high level indicates hypothyroidism and a low level indicates hyperthyroidism.

    • T3 and T4 tests: to directly measure hormone levels.

    • Thyroid antibodies (Anti-TPO, Anti-TSH receptor): to detect autoimmune diseases.

    • Ultrasound: to evaluate the size of the gland and nodules.

  • Conclusion

  • The thyroid gland represents a fundamental hub in the endocrine network, as it controls metabolic rates, energy production, and the regulation of multiple functions including growth, nervous system development, and cardiovascular health. Therefore, any disorder in its function, whether hypothyroidism or hyperthyroidism, is directly reflected in all body systems. Hypothyroidism leads to slow metabolism, weight gain, lethargy, and impaired concentration, while hyperthyroidism causes accelerated metabolism, unexplained weight loss, anxiety, and a rapid heart rate. These disorders are associated with several factors such as the autoimmune diseases Hashimoto's and Graves' disease, iodine deficiency or excess, postpartum hormonal changes, in addition to genetic and environmental factors. Thyroid disorders also interfere with other problems such as obesity and insulin resistance, which highlights their importance in the overall metabolic balance of the body. Acknowledging this close relationship between the thyroid gland and human health reinforces the need to raise societal awareness about its vital role and the importance of regular check-ups, as it is a cornerstone of the stability of the body's overall health.