Thyroid-stimulating hormone

TSH is produced by the pituitary gland in the brain, and its job is to signal the thyroid gland to make more or less thyroid hormone (thyroxine and triiodothyronine). It works like a thermostat: when thyroid hormone levels are low, TSH rises to push the thyroid to produce more; when thyroid hormone levels are high, TSH drops. A simple blood test measures TSH and is usually the first step in checking thyroid function.

TSH levels matter for bone health because thyroid hormone directly affects how fast bone is broken down and rebuilt. When TSH is low and thyroid hormone is high, a condition called hyperthyroidism, bone turnover speeds up and this can lead to bone loss over time. Even mildly low TSH without obvious symptoms, known as subclinical hyperthyroidism, has been linked to lower bone density in some people. On the other end, an underactive thyroid (high TSH, low thyroid hormone) is called hypothyroidism and does not typically cause the same bone loss pattern, but untreated thyroid problems in general are worth addressing.

If you take thyroid hormone replacement, such as levothyroxine, your doctor will periodically check TSH to make sure your dose is in the right range, since too much replacement hormone can also push TSH too low and affect bones over the long run. Any changes to thyroid medication dosing should always be guided by your prescriber, not adjusted on your own.