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Bone is a metabolically
highly active tissue. Various factors are necessary to ensure
normal skeletal growth, maturation and turnover. Well known
calciotropic hormones include parathyroid hormone (PTH),
calcitonin (CT) and 1,25-dihydroxyvitamin D. They act together
with locally produced factors to regulate the activity of bone
cells and calcium metabolism. Apart from these, sufficient levels
of thyroid hormones are also important for normal skeletal
development, a fact which was already recognised over 100 years
ago by von Recklinghausen. The most dramatic example of the
importance of thyroid hormone for skeletal development is seen in
untreated congenital hypothyroidism. Findings include shortness
of stature, infantile skeletal proportions, with relatively short
extremities, retarded "bone age" and epiphyseal
dysgenesis. On the other hand, hyperthyroidism is one of the
causes of secondary osteoporosis.
In the following, we will discuss the effects of thyroid hormone on bone at cellular and tissue level. Furthermore, we will review the effects of both hyper- and hypothyroidism on markers of bone turnover, bone mineral density and fractures. |
