TSH (Thyroid-Stimulating Hormone)

Routine annual

also thyrotropin

What it isTSH is released by the pituitary gland in response to falling circulating thyroid hormone. It instructs the thyroid to make and release more T4 and T3.

DoesActs as the body's thermostat for thyroid output — rising when thyroid hormone is low, falling when it's adequate.

GoodA mid-low TSH with adequate Free T4 and Free T3 signals a smoothly running thyroid axis.

BadHigh TSH signals hypothyroidism (the thyroid isn't keeping up). Low TSH suggests hyperthyroidism or, less commonly, pituitary failure.

Standard

0.4–4.5 mIU/L.

Optimal

0.8–1.8 mIU/L (narrow target)

Modifiers

Higher in the morning, falls overnight; rises with stress and acute illness; biotin supplements interfere with the assay.

How to optimize

Lifestyle: Manage stress; sleep 7–9 hours; resistance training; avoid extreme caloric restriction.
Diet: Adequate iodine, selenium, zinc, and iron; avoid extreme low-carb in some who develop euthyroid-low-T3 syndrome.
Supplements: Selenium (200µg/day), zinc (15–30mg/day), iodine (only if deficient and not in autoimmune thyroid disease), iron if low.
Peptides: —
Drugs: Levothyroxine for hypothyroidism; methimazole, propylthiouracil, radioactive iodine for hyperthyroidism.

within Thyroid