The effects of subclinical thyroid dysfunction on bone mineral density and fracture risk in men and women remain unclear, with two studies published in the Journal of Clinical Endocrinology & Metabolism yielding conflicting results.

“Although overt thyrotoxicosis is known to cause loss of bone mineral density (BMD), osteoporosis, and propensity to fracture, it remains controversial whether similar risk applies to mild states of T4 excess with normal reference range T4 and T3 levels but suppressed [thyroid-stimulating hormone (TSH)] levels, ie, ‘subclinical’ hyperthyroidism,” Leonard Wartofsky, MD, of MedStar Washington Hospital Center in Washington, D.C., wrote in an accompanying editorial.

Fueling the Controversy

The first study conducted by Margaret C. Garin, MD, of the Perelman School of Medicine at the University of Pennsylvania in Philadelphia, and colleagues assessed the associations between subclinical hyperthyroidism or subclinical hypothyroidism and hip fracture or BMD in elderly participants from The Cardiovascular Health Study.

The researchers assessed incident hip fracture by thyroid status in 4,936 adults aged at least 65 years who were not taking thyroid preparations. A subset of 1,317 participants who underwent dual-energy x-ray absorptiometry scans (DEXA) were included in a cross-sectional analysis of thyroid status and BMD.

In women, subclinical hypothyroidism was not associated with incident hip fracture, as compared with euthyroidism, at a single time point (HR=0.91; 95% CI, 0.69-1.20) or persisting at two time points (HR=0.79; 95% CI, 0.52-1.21).

There was also no association between subclinical hypothyroidism and incident hip fracture in men at a single time point (HR=1.27; 95% CI, 0.82-1.95) or persisting at two time points (HR=1.09; 95% CI, 0.57-2.10).

Similarly, subclinical hyperthyroidism did not appear to be associated with incident hip fracture in women (HR=1.11; 95% CI, 0.55-2.25) or men (HR=1.78; 95% CI, 0.56-5.66).

Results also failed to demonstrate a link between BMD and subclinical thyroid dysfunction at the lumbar spine, total hip or femoral neck.

“Our data suggest no association between subclinical hypothyroidism or subclinical hyperthyroidism and hip fracture risk or BMD in older men and women,” the researchers wrote.

“Additional data are needed to improve the precision of estimates for subclinical hyperthyroidism and in men.”