Thyroid hormones are essential for normal bone strength. Bones aren’t static, like rocks. Throughout our lives, the cells in bones break down and regrow, a process known as remodeling. A proper balance of breaking down and rebuilding bone tissue is needed for bones to stay strong during our lifetimes. As we age, bone tends to break down more quickly and rebuild more slowly. For women, the first 5-10 years after menopause are a period of accelerated bone breakdown. It’s especially important to try to minimize bone breakdown during this time to maximize healthy bones for a long time.
Thyroid hormones affect both sides of the bone remodeling equation. Hyperthyroidism–an overactive thyroid–can accelerate bone breakdown and cause osteoporosis–literally, weak porous bones. Hypothyroidism–low thyroid function–clearly causes impaired bone formation in children. In adults, the effects of hypothyroidism are less clear, but, over time, could also lead to weaker bones.
The biggest point of contention when it comes thyroid and your bones is thyroid stimulating hormone (TSH). That’s the hormone that is secreted from your pituitary gland in response to low blood levels of thyroid hormones. TSH signals your thyroid gland to secrete more T4. The traditional thinking is that a low blood level of TSH means that your thyroid hormone levels are too high and are causing bone loss.
TSH alone does not adequately reflect the complexity of thyroid system physiology. TSH is very helpful in evaluating thyroid hormone supply, but not necessarily utilization. Research shows that signs and symptoms are the best indicators of thyroid hormone activity in the tissues.
In the most extensive review published to date on the risk of bone loss or osteoporosis from TSH-suppressive doses of thyroid (which analyzed data in 28 studies) the authors concluded that that there is no effect of TSH suppression on bone density.
I believe that the experience of people taking T3 (rather than T4) may be positive when it comes to bone. When people have normal body temperatures, possibly due to taking T3, their enzymes that help rebuild bone are more likely to be functioning well than people whose body temperatures remain low. Many thousands of people have used T3 therapy over the past 15-20 years, sometimes in doses that do indeed suppress TSH but also correct body temperature and relieve other symptoms. And I have not heard reports of increased osteoporosis or bone loss in these patients. Indeed, better temperatures may even improve bone enzyme function.
I would suggest that if you have low body temperature, that you do what you can to normalize it to see if you feel better. If you are already at risk for osteoporosis and you decide to try T3, you could always monitor your bone mineral density to see if it improves or worsens in your case. It’s also a good idea to take enough vitamin D and calcium.
In my mind, probably the worst way to use thyroid medicine is continuing to give people TSH-suppressive doses of T4 even though they continue to have low temperatures and low thyroid symptoms. I wouldn’t be surprised by increased bone loss in that setting. In fact, one study reported increased bone loss in patients given suppressive doses of T4 for over 10 years. It appears that the patients were being treated irrespective of their temperatures or symptoms since no mention was made of them.
Bassett JH, Williams GR. The molecular actions of thyroid hormone in bone. Trends Endocrinol Metab. 2003 Oct;14(8):356-64.
Zulewski H, Muller B, Exer P, Miserez AR Staub JJ. Estimation of tissue hypothyroid by a new clinical score: Evaluaton of patients with various grades of hypothyroidism and controls. JCEM 1997;82:771-776
Dinesh Kumar Dhanwal. Thyroid disorders and bone mineral metabolism. Indian J Endocrinol Metab. 2011 July; 15(Suppl2): S107–S112.
Galliford TM, Murphy E, Williams AJ, et al. Effects of thyroid status on bone metabolism: a primary role for thyroid stimulating hormone or thyroid hormone? Minerva Endocrinol. 2005 Dec;30(4):237-46.
Gorka J, Taylor-Gjevre RM, Arnason T. Metabolic and clinical consequences of hyperthyroidism on bone density. Int J Endocrinol. 2013;2013:638727. doi: 10.1155/2013/638727. Epub 2013 Jul 22
Lakatos P. Thyroid hormones: beneficial or deleterious for bone? Calcif Tissue Int. 2003 Sep;73(3):205-9.
Murphy E, Williams GR. The thyroid and the skeleton. Clin Endocrinol (Oxf). 2004 Sep;61(3):285-98.
U.S. Preventive Services Task Force. Screening for osteoporosis: recommendation statement. Am Fam Physician. 2011 May 15;83(10):1197-200.