TSH: The Pituitary-Thyroid Go-Between

Thyroid-stimulating hormone (TSH) is produced in the pituitary gland, but its job is to stimulate the thyroid into producing more thyroid hormone when its levels decline. Since the thyroid gland is a major regulator of metabolism, producing too much or too little thyroid hormone will affect organs and cells throughout the body. Therefore, too much or too little TSH will affect metabolism throughout the body as well, including a direct effect on cardiometabolic health. 

A low TSH is associated with hyperthyroidism which occurs when the thyroid produces too much thyroid hormone and feeds back to reduce TSH. A low TSH may also occur if the pituitary does not produce enough TSH. Decreased TSH can also be associated with the use of certain medications.

An elevated TSH is associated with hypothyroidism which can occur if the thyroid cannot produce adequate thyroid hormone; High TSH is also associated with thyroid inflammation, excess iodine, chronic and severe illness, increased cardiovascular risk, and the use of certain medications. 

A simple rule of thumb to remember is: 

If TSH is low and thyroid hormones are also low, the pituitary is likely at fault. If TSH is high and thyroid hormones are low, the thyroid is most likely at fault.

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