What do thyroid problems have to do with osteoporosis?

Both an overactive and an underactive thyroid increase the risk of bone loss. With an overactive thyroid, bone is broken down faster than it is built up. Genetic research points to a causal effect: people with a predisposition to hyperthyroidism have roughly 17% higher odds of developing osteoporosis, although one other study did not find this association. The link with reduced bone density is most clearly visible in older women (post-menopause) and men over fifty.

An underactive thyroid is also associated with weaker bones. Genetic research suggests that hypothyroidism raises the risk of osteoporosis by around 10-11%. Hashimoto's thyroiditis, an autoimmune disease in which the body's own immune system attacks the thyroid, also appears to affect bone strength: people with a genetic predisposition to this condition have roughly 14% higher odds of osteoporosis.

Even a mild, 'silent' form of an overactive thyroid, in which thyroid hormone levels are still normal but the control signal from the brain is already too low, increases the risk of fractures and osteoporosis. This is shown by several studies, although these findings are associations that have not yet been fully proven as cause and effect.

The evidence on thyroid hormone supplementation as a risk factor for bone loss is thin. There is an old signal that long-term use of thyroid hormone medication may affect the bones, but based on the available information little of substance can be said about this. If you have a thyroid condition and are concerned about your bones, discuss with your doctor whether your TSH level is well controlled and whether a bone density measurement would be worthwhile.