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 (which in turn may cause osteopenia and then osteoporosis).
But as of 2019, the truth is that real science still indicates that suppressed TSH is not responsible for bone loss.
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.
https://academic.oup.com/mend/article/21/5/1095/2738372
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:
https://onlinelibrary.wiley.com/doi/full/10.1002/jbmr.3426
A full discussion of this topic has been written by Canadian Thyroid Patients Campaign thyroid patient advocate/writer Tania S. Smith:
https://thyroidpatients.ca/2019/07/12/as-of-2019-still-no-proof-that-low-tsh-causes-harm-to-bones/
Apart from hyperthyroidism, one of the reasons that some doctors have jumped to the conclusion that there is a link between low TSH and bone turn-over is that because bone cells express a functional TSH receptor on their surface. So, the TSH can connect to this receptor. However, any potential TSH effect is interwoven with other signals such as by thyroid hormones and estrogens,. There is redundancy in the system. This means what happens is highly depends on the specific condition and combinations, not a sole influence. It is also very difficult to isolate the TSH effect, because it is not the same to everybody. Furthermore, it is extremely difficult to create a proper controlled experiment when thyroid hormones and estrogens are all perfect yet TSH is low. There has to be an individualised approach, as outlined in the following review: Hoermann R, Midgley JEM, Larisch R, Dietrich JW. Individualised requirements for optimum treatment of hypothyroidism: Complex needs, limited options. Drugs Context. 2019;8:212597. doi:10.7573/dic.212597. See:
https://pmc.ncbi.nlm.nih.gov/articles/PMC6726361/
The biggest causes of bone loss, potentially leading to osteoporosis in women are:
1) Low oestrogen.
and
2) Low thyroid hormones, especially low FT3.
So, testing oestrogen, progesterone, TSH, FT4, FT3 and ideally rT3 is important so that any potential cause of bone loss can be identified and corrected. Also testing vitamin D levels is important too, as low vitamin D results in poor calcium absorption. My The Thyroid Patient’s Manual book shows you how to interpret the vitamin D result and what supplements to use to correct low vitamin D.
Addressing low oestrogen is essential, whilst balancing with progesterone. Remaining clinically hypothyroid is in itself a big risk of bone loss, which may develop into detectable osteopenia and ultimately osteoporosis. Going simply on TSH and FT4 is a big mistake.
Having low FT3 and clinical signs/symptoms of being hypothyroid are what should tell the person and their doctor that this needs to be treated. Hypothyroidism requires treating with the right level and combination of thyroid hormones for the individual (not just being put on levothyroxine and monitoring TSH level). Remaining with hypothyroid symptoms is a big risk for osteoporosis. The level of TSH is not linked to osteoporosis when a thyroid patient is receiving thyroid medication that is properly managed for them, i.e. with the right level of FT3 thyroid hormone.
Treating any low oestrogen issue and any clinical hypothyroidism issue can halt and sometimes reverse bone loss in women.
I actually know of thyroid patients who have built bone when their T3 doses have become optimal for them, even when they had low TSH.
Best wishes,
Paul
