Adrenals and Thyroid: How Cortisol Impacts Thyroid Hormone Metabolism

The adrenal glands and the thyroid gland are two essential components of the endocrine system that work closely together to regulate various physiological processes in the body. The adrenal glands produce a hormone called cortisol in response to stress, and cortisol plays a crucial role in regulating many physiological processes, including metabolism. However, imbalances in cortisol levels can negatively affect thyroid hormone metabolism and contribute to symptoms of hypothyroidism.

High levels of cortisol can lead to an increase in thyroid-binding globulin (TBG), a protein that binds thyroid hormone in the blood, making less thyroid hormone available to enter the cells and do its job. This can result in symptoms of hypothyroidism, despite "normal looking" thyroid hormone levels in the blood. On the other hand, low levels of cortisol can also negatively affect thyroid hormone metabolism. Cortisol helps to convert the inactive thyroid hormone T4 into the active thyroid hormone T3, which is responsible for the metabolic effects of thyroid hormone. Without adequate cortisol, T4 may not be converted efficiently into T3, leading to symptoms of hypothyroidism.

Therefore, it's crucial to test for both cortisol and thyroid hormones to identify any imbalances that may be contributing to symptoms. Low levels of cortisol can lead to a decrease in the production of TSH, the hormone that stimulates the thyroid gland to produce thyroid hormone. This can result in low thyroid hormone levels and symptoms of hypothyroidism.

Furthermore, cortisol can increase the production of reverse T3 (rT3) through a process known as "thyroid hormone diversion." When cortisol levels are high, the body may divert more T4 toward the production of rT3 instead of active T3. This occurs because cortisol affects the activity of an enzyme called iodothyronine deiodinase, which is responsible for converting T4 to both T3 and rT3. High levels of cortisol can increase the activity of the deiodinase enzyme that converts T4 to rT3, leading to an increase in rT3 levels.

The production of rT3 is a protective mechanism that helps the body conserve energy during times of stress. By producing more rT3, the body slows down metabolism and conserves energy, which can be useful in situations where energy needs to be conserved for other bodily processes. However, if cortisol levels remain high for an extended period, it can lead to an excess of rT3 and a relative deficiency of active T3, which can contribute to symptoms of hypothyroidism.

In summary, the adrenal glands and the thyroid gland work closely together, and cortisol plays a crucial role in regulating thyroid hormone metabolism. Imbalances in cortisol levels can negatively affect thyroid hormone metabolism and contribute to symptoms of hypothyroidism. Testing for both cortisol and thyroid hormones can help identify any imbalances that may be contributing to symptoms.