Thyroid Hormone Functions and Regulation

Metabolic Functions

T3 regulates daily rhythms in glucose metabolism, with faster glucose clearance occurring during the early active phase, according to the American College of Endocrinology 1
T3 controls lipolysis and fatty acid oxidation during fasting states, influencing serum triglyceride levels and overall lipid metabolism, as stated by the American Association of Clinical Endocrinologists 1
T3 increases the force and speed of systolic contraction and the speed of diastolic relaxation in cardiac tissue, affecting heart function, as reported by the American Heart Association 2

T3 decreases systemic vascular resistance, including coronary vascular tone, as found by the American Heart Association 2
T3 increases resting heart rate and left ventricular contractility, according to the American College of Cardiology 2
T3 enhances isovolumic ventricular relaxation, improving cardiac function, as stated by the American Heart Association 2

T3 is involved in the tissue conversion of T4 to T3 within the thyroid gland itself, as reported by the Endocrine Society 3, 4
T3 participates in thyroid-stimulating hormone (TSH) secretion regulation through negative feedback, according to the Endocrine Society 4, 5

T3 is crucial for bone health, influencing the production of collagen type I through hydroxylases that require iron for their catalytic activity, as found by the International Osteoporosis Foundation 4, 5
T3 affects bone mineral density and overall bone health, according to the National Osteoporosis Foundation 5

T3 production is primarily regulated by thyroid-stimulating hormone (TSH) from the pituitary gland, as stated by the American Thyroid Association 6
T3 shows distinct daily rhythmic patterns that differ between diurnal humans and nocturnal rodents, according to the American Association of Clinical Endocrinologists 1

Abnormal T3 levels can lead to thyroid dysfunction, manifesting as either hypothyroidism (insufficient T3) or hyperthyroidism (excess T3), as reported by the American Thyroid Association 6
T3 deficiency can result in decreased metabolic rate, while excess T3 increases metabolic rate, according to the American Association of Clinical Endocrinologists 1
Iron deficiency can impair the conversion of T4 to T3, affecting thyroid function, as found by the National Institutes of Health 4, 6
Selenium is required for the deiodination of T4 to T3 via the selenoenzyme Type 1 5'-deiodinase, as stated by the American Thyroid Association 6