Hyperthyroidism is a risk factor for osteoporosis and fractures, so are patients who take long term thyroxine replacement at increased risk of fractures? Some studies have shown an increased risk of fracture for patients with low concentrations of thyroid stimulating hormone (TSH) who take long term thyroxine,1 2 but others have not.3 4 This discrepancy may be due to confounding as a result of patient selection, the background fracture risk in the population, the power of the studies, and inclusion of patients with a history of hyperthyroidism who are on long term thyroxine replacement.

A recent cohort study included 17 684 patients with primary hypothyroidism and serial TSH estimations rather than baseline measurements only.5 It found a statistically significant increased risk of fractures in patients of all ages taking long term thyroxine who had suppressed serum TSH concentrations (<0.03 mU/L) but not in patients with a low TSH (0.04-0.4 mU/L) or TSH in the reference range.

In the linked nested case-control study of 213 511 patients over the age of 70 years who were taking thyroxine for primary …