Hyperthyroidism and Bone Health

The importance of thyroid hormone in skeletal development is signified by childhood hypothyroidism which leads to delayed skeletal maturation and growth arrest and thyrotoxicosis, which is associated with accelerated skeletal development in children. In adults, thyrotoxicosis results in increased bone remodeling [1] . Both hypothyroidism and hyperthyroidism affect bone mineral density (BMD) and are associated with increased risk of fragility fracture [2] . Thyrotoxicosis affects bone much more than hypothyroidism and is an important cause of secondary osteoporosis. Like other systemic manifestations of thyrotoxicosis, bone disease in Indian patients is more severe due to the fact that Indian patients present late during the disease course. Thyroid hormones directly affect the remodeling process by their action on osteoblasts, which indirectly stimulate the osteoclasts through cytokines. Osteoclast activity is increased by thyroid hormone but only in the presence of osteoblasts. The duration of remodeling cycle is reduced by 50%. The uncoupling of remodeling process leads to a net bone loss that can amount to 10% of mineralized bone per cycle in severe cases of thyrotoxicosis [3] .