Bones thyroid hormones effect

Therapy with levothyroxine is very safe, provided that thyroid hormone levels are monitored and maintained within the normal range. Excess doses of T4 are associated with a loss of bone mass. A meta-analysis of 41 controlled studies on the impact of thyroid hormone therapy on bone mineral density (Uzzan et al., 1996) has shown that doses of T4 that suppress thyrotropin (TSH) secretion are associated with a significant loss of bone in the lumbar spine and hip in postmenopausal women. Another review of the evidence of the thyroid hormone effect of on skeletal integrity concluded that hyperthyroidism and the use of thyroid hormone to suppress TSH seem to have an adverse effect on bone, especially in postmenopausal women (Greenspan and Greenspan, 1999) however, thyroid hormone replacement seems to have a minimal effect on bone. 

Management of hypothyroidism consists of identifying the underlying cause and then providing thyroid hormone replacement to normalize thyroid sta-ms. The goal of treatment is to reduce semm TSH levels to normal, which for most assays is roughly between 0.5 and 3 mU/1. Oversuppression of TSH levels is probably not advisable, as overtreatment may predispose to cardiac arrhythmias (particularly atrial fibrillation), and may have subtle effects on bone mineral density. 

In 50 women taking levothyroxine either for primary thyroid failure or for hypothyroidism secondary to radioiodine treatment for hyperthyroidism, there was no difference between the two groups in terms of bone density at the hip or spine and no difference from the reference population (31). In addition, there was no correlation between bone density and circulating thyroid hormone concentrations or duration of levothyroxine replacement. These findings are reassuring, although large studies of fracture risk are required, in view of previous evidence of an adverse effect of levothyroxine on bone mineral density, especially in post-menopausal women (32). 

Table 1 Summary of studies on the effects of thyroid hormones on bone mineralization...

Data from more than 30 studies of the effect of thyroid hormone on bone have been reviewed (37). The results have supported the view, expressed before (38), that there is a small, but statistically significant, adverse effect on bone mineral density, especially in postmenopausal women. 

Uzzan B, Campos J, Cucherat M, Nony P, Boissel JP, Perret GY. Effects on bone mass of long term treatment with thyroid hormones a meta-analysis. J Clin Endocrinol Metab 1996 81(12) 4278-89. 

Krolner B, Jorgensen JV, Nielsen SP. Spinal bone mineral content in myxoedema and thyrotoxicosis. Effects of thyroid hormone(s) and antithyroid treatment. Clin Endocrinol (Oxf) 1983 18(5) 439 16. 

Stathatos NWL. Effects of thyroid hormone on bone. Clin Rev Bone Mineral Metab 2005 2 135-50. 

Hypothyrodism and hyperthyroidism can both be due to a number of causes, one of which is metabolic dysfunction. Hypothyroidism is caused by undersecretion, of thyroid hormones. In one form of childhood hypothyroidism, children born with abnormally small thyroids produce insufficient levels of the thyroid hormones T3 and T4, which are important for metabolically directed bone development. If detected in the first 6 months of life, this disorder can be treated with synthetic thyroid hormones such that its effects can be avoided. The most severe early onset hypothyroidisms are characterized by Cretinism, a type of dwarfism, and mental retardation. Adult hypothyroidism is called myxedema. Myxedema symptoms include slowed speech, yellowed skin, and generally slowed body functions. Myxedema can also be treated with synthetic T4, but if left untreated, can lead to coma. 

Prolonged overtreatment with levothyroxine can result in osteopenia (23). Thyroid hormones have a direct effect on bone cells, thereby increasing both bone resorption... 

Increased metabolism, increased heat production, weight loss, protrusion of the eyes (exophthalmia), and an increase in bone and muscle turnover are the major symptoms. In addition, increased levels of thyroid hormone have detrimental effects on cardiac muscle and cardiac conduction, as well as on vascular smooth muscle function. 

Uses Thyroid hormones, levothyroxine (T4), and triiodothyronine (liothyronine, T3) are used to treat hypothyroidism. Both overt and subclinical hypothyroidism are associated with dyslipidemia, and replacement with thyroid hormones lowers the concentrations of serum low-density lipoprotein (LDL) cholesterol and has other potentially favorable actions on lipoprotein metabolism [1 ]. Consequently, thyro-mimetic drugs, which mimic the actions of thyroid hormones, hold promise as lipidlowering agents. The development of some of these drugs was discontinued because of adverse reactions related to thyroid hormone-like actions, including possible death due to cardiac causes and adverse effects on bone [2 , 3 ]. 

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