Synopsis

Source of validity: Scientific
Rating (out of 5): 4

Desiccated thyroid extract, often simply called "Thyroid," is a preparation derived from animal thyroid glands and has been used in medicine for over a century to treat hypothyroidism and related conditions. The primary role of thyroid hormones (T3 and T4) in the body is to regulate metabolism, but they also significantly influence the sympathetic nervous system (SNS). Scientific research demonstrates that thyroid hormones increase the number and sensitivity of beta-adrenergic receptors on cells, thereby enhancing the body's response to catecholamines (e.g., adrenaline and noradrenaline), which are mediators of the SNS. This upregulation results in increased heart rate, cardiac output, and basal metabolic rate, all of which are hallmarks of sympathetic nervous system activation.

Clinical studies and endocrinology textbooks consistently note that hyperthyroidism (excess thyroid hormone) often presents with symptoms of SNS overactivity, such as palpitations, anxiety, and tremors. Conversely, hypothyroidism is associated with reduced SNS activity, including bradycardia and fatigue. Therefore, thyroid supplementation in hypothyroid individuals can restore normal SNS function. However, the use of thyroid extract specifically to "support" the SNS in individuals with normal thyroid function is not supported by scientific evidence and may be unsafe. The evidence base for thyroid's effect on the SNS is robust and mechanistically well understood, but its use should be limited to correcting thyroid hormone deficiencies, not for general SNS support in otherwise healthy individuals.

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