From the Guidelines
Thyroid hormone plays a crucial role in maintaining overall health, and its imbalance can significantly impact morbidity, mortality, and quality of life. The importance of thyroid hormone in the body cannot be overstated, as it regulates metabolism, energy production, and affects nearly every organ system 1. Thyroid hormone controls how quickly cells convert nutrients into energy, influencing heart rate, body temperature, and brain development, particularly during fetal development and early childhood. It also has a significant impact on muscle control, digestive function, bone maintenance, and cholesterol levels.
Key Functions of Thyroid Hormone
- Regulates metabolism and energy production
- Influences heart rate and body temperature
- Essential for brain development, particularly during fetal development and early childhood
- Affects muscle control, digestive function, and bone maintenance
- Plays a role in maintaining healthy cholesterol levels
Without adequate thyroid hormone, metabolism slows dramatically, leading to fatigue, weight gain, cold intolerance, and depression (hypothyroidism) 1. On the other hand, excess thyroid hormone causes hypermetabolism, resulting in weight loss, anxiety, heat intolerance, and rapid heartbeat (hyperthyroidism). The thyroid gland produces two main hormones: thyroxine (T4) and triiodothyronine (T3), with T4 being converted to the more active T3 in tissues.
Regulation of Thyroid Function
- Thyroid function is regulated by a feedback loop involving the hypothalamus and pituitary gland
- The hypothalamus and pituitary gland release TRH and TSH respectively to maintain proper hormone levels
- Iodine is a critical component needed for thyroid hormone production, and its deficiency can lead to thyroid disorders 1.
In terms of treatment, the current evidence does not show important benefits of treatment of subclinical thyroid dysfunction on blood pressure, BMI, lipid levels, cognitive function, or quality of life 1. However, treatment may have important long-term benefits on final health outcomes, such as cardiovascular-related morbidity and mortality. Therefore, it is essential to carefully evaluate the risks and benefits of treatment for each individual patient, taking into account their specific clinical context and health outcomes.
From the FDA Drug Label
Thyroid hormones exert their physiologic actions through control of DNA transcription and protein synthesis. The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues.
The importance of thyroid hormone in the body is to regulate DNA transcription and protein synthesis. Thyroid hormones, particularly T3, play a crucial role in producing the physiological actions that are essential for the body's functioning. 2
- Key functions: control of DNA transcription and protein synthesis
- Main physiological action: produced predominantly by T3, derived from T4 by deiodination in peripheral tissues
From the Research
Importance of Thyroid Hormone
The thyroid hormone plays a crucial role in various bodily functions, including:
- Metabolic regulation: Thyroid hormone is essential for maintaining metabolic homeostasis, and its dysregulation can lead to metabolic disorders 3, 4.
- Cardiovascular system: Thyroid hormone has profound effects on the heart and cardiovascular system, influencing cardiovascular hemodynamics and metabolism 5.
- Growth and development: Thyroid hormone is necessary for growth, differentiation, and development, and its deficiency can lead to growth and developmental abnormalities.
- Energy homeostasis: Thyroid hormone signaling modulates energy expenditure through both central and peripheral pathways, maintaining energy homeostasis 4.
Consequences of Thyroid Hormone Imbalance
An imbalance of thyroid hormone can have severe consequences, including:
- Hyperthyroidism: Excessive production of thyroid hormone can lead to cardiac arrhythmias, heart failure, osteoporosis, and adverse pregnancy outcomes 6, 7.
- Hypothyroidism: Deficiency of thyroid hormone can cause fatigue, weight gain, and dry skin, among other symptoms.
- Thyrotoxicosis: A condition characterized by high levels of thyroid hormone, which can cause anxiety, insomnia, palpitations, and unintentional weight loss 7.
Regulation of Thyroid Hormone
The regulation of thyroid hormone is complex and involves:
- Thyroid hormone receptors: Thyroid hormone exerts its effects by binding to thyroid hormone receptors, which modulate the expression of target genes 3.
- Deiodinases: Enzymes that convert thyroid hormone into its active form, triiodothyronine (T3) 4.
- Transmembrane transporters: Proteins that facilitate the transport of thyroid hormone into cells 4.