Many guidelines strongly caution against the risk associated with low TSH.
Some doctors and thyroid patients have jumped to the conclusion that a low TSH ’causes’ osteoporosis.
Some even believe a low TSH must be avoided at all costs during thyroid therapy, even if lowering their thyroid hormone dose causes chronic hypothyroid symptoms in a patient!
But as of 2019, the truth is that real science still indicates that suppressed TSH is not responsible for any harm to bones.
In 2007 Bassett et al stated, “Thyroid hormone excess rather than thyrotropin (TSH) deficiency induces osteoporosis in hyperthyroidism”. Note: this means too much thyroid hormone for the patient is a risk for osteoporosis, but this means they would usually have hyperthyroid symptoms. Low TSH itself is not an issue.
Here is the 2007 study:
“Thyroid hormone excess rather than thyrotropin deficiency induces osteoporosis in hyperthyroidism”.
Bassett, J. H. D., O’Shea, P. J., Sriskantharajah, S., Rabier, B., Boyde, A., Howell, P. G. T., … Williams, G. R. (2007). Endocrinology (Baltimore, Md.), 21(5), 1095–1107.
In 2018 Van Vilet et al stated, “We found no evidence for a causal effect of circulating TSH on BMD (Bone Mineral Density)”.
Here is the 2018 study:
“Thyroid Stimulating Hormone and Bone Mineral Density: Evidence From a Two-Sample Mendelian Randomization Study and a Candidate Gene Association Study”.
Van Vliet NA, Noordam R, van Klinken JB, et al. J Bone Miner Res Off J Am Soc Bone Miner Res. March 2018.
https://www.ncbi.nlm.nih.gov/pubmed/29544020 and full article:
A full discussion of this topic has been written by Canadian Thyroid Patients Campaign writer/researcher Tania S. Smith:
Low thyroid hormones are more of a concern for osteoporosis, alongside low oestrogen in women.
I actually know of thyroid patients who have built bone when their T3 doses have become optimal.