Effect of Thyroid Disorders on Skeletal Health

ABSTRACT

Thyroid physiology is linked to skeletal health. T3 and TSH independently affect bone growth and development, mineralization and remodeling. Thyrotoxicosis, a clinical syndrome characterized by excess thyroid hormone is one of the commonly recognized conditions of the thyroid gland. Thyrotoxicosis causes accelerated bone remodeling and serves as one of the risk factors for osteoporosis. Treatment of thyrotoxicosis leads to reversal of bone loss and decreases fracture risk. Though treatment of thyrotoxicosis leads to improvement of bone mineral density (BMD), it is not necessarily to normal levels. The effects of subclinical hyperthyroidism on the bone are controversial.  Thyroidectomy and methimazole may decrease the risk of fractures in these patients compared with treatment with radioiodine. Hypothyroidism may also be risk factor for fractures. Replacement therapy with levothyroxine in hypothyroid patients may temporarily reduce bone density after initiation of therapy. However it is not associated with  osteoporosis or increased fracture risk. TSH suppressing doses of levothyroxine may reduce BMD, especially in post menopausal women.  Supplementation of calcium and vitamin D in hyperthyroid patients should be considered. There are limited studies in India pertinent to reversibility of these changes. In this review, we have discussed about the effects of various aspects of skeletal health in thyroid disorders.