A new study published in the Journal of Clinical Endocrinology and Metabolism reveals that healthy postmenopausal women with slightly elevated levels of thyroid function are at a higher risk for low bone mineral density (BMD) and therefore fractures.
Researchers from the Molecular Endocrinology Group at the Imperial College of London tested thyroid hormone levels of 2,000 women over six years. At the end of the study, they found that those with higher levels of free thyroxine (T4) and triiodothyronine (T3) had significantly lower BMD and bone loss at the hip.
After adjustment for age, body mass index and BMD, the risk of fracture was increased by 20 percent in women with higher T4 and by 33 percent in those with higher levels of T3. However, increased levels of thyroid stimulating hormone (TSH) reduced the risk of such fractures by 35 percent. Also, TSH was not associated with changes in BMD, bone turnover markers or other soft tissue measures.
"These findings reveal novel interactions between T3 and the cardiovascular and neuromuscular systems that could modify the relationship between thyroid status and bone maintenance, and complicate analysis of the mechanisms by which the hypothalamic-pituitary-thyroid axis regulates BMD and fracture susceptibility," the authors wrote. "Thyroid status may be a physiological determinant of bone maintenance."