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2. Thyroid Stimulating Hormone (TSH)

What is TSH?

Thyroid stimulating hormone (TSH) is produced by the pituitary gland at the bottom of the brain. Its job is to tell the thyroid how much thyroid hormone to make. [3]

tsh stimulates the thyroid gland to make thyroid hormone. TSH levels depend on the pituitary gland.

TSH levels

Normally, if you have too little thyroid hormone, the pituitary will make more TSH, to tell the thyroid to make more hormone. Therefore, high TSH indicates low levels of thyroid hormone (hypothyroidism). [4]

Likewise, if you have too much thyroid hormone, the pituitary will make less TSH, to tell the thyroid to make less hormone. Therefore, Low TSH can indicate high levels of thyroid hormone (hyperthyroidism). [5]

The following chart shows how TSH levels change when there is a disease of the thyroid gland.

Thyroid function Pituitary Thyroid gland
Normal Produces enough TSH to stimulate thyroid gland, but not too much Produces proper amount of thyroid hormone
(low thyroid hormone)
Makes more TSH to tell the thyroid to make more thyroid hormone. Due to thyroid disease, the thyroid gland cannot respond to increased TSH and still makes too little thyroid hormone.
Hyperthyroidism (high thyroid hormone) There is already too much thyroid hormone, so the pituitary makes very little TSH. Due to thyroid disease, the thyroid makes excessive amounts of thyroid hormone despite less stimulation from the pituitary gland and TSH.

Doctors often depend solely on TSH to diagnose and treat hypothyroidism. Other labs tests and clinical observation are often ignored. The medical establishment's over reliance on TSH causes under diagnosis of hypothyroidism. [6]

Why we can't use TSH as the only measure of thyroid function:

The reference range for TSH is too large.

According to The National Institutes of Health's (NIH) web site, normal TSH reference range is 0.4 – 4.0. The NIH article goes on to say:

Those without signs or symptoms of an under active thyroid who have a TSH value over 2.0 mIU/L but normal T4 levels may develop hypothyroidism in the future. This is called subclinical hypothyroidism (mildly under active thyroid) or early-stage hypothyroidism. Anyone with a TSH value above this level should be followed very closely by a doctor.”[7]

While it is good to see more mainstream sources recognizing the insufficiency of relying solely on TSH reference ranges, the above recommendations are still lacking.

There is nothing in the above about prevention. Instead they recommend monitoiring TSH.

Monitoring disease progression is not prevention. It's sort of like putting up a dozen cameras around a dangerous intersection so the next accident can be caught on tape. True prevention stops the disease from happening. People need to do more than just wait until their TSH becomes bad enough for thyroid drugs.