Interrelationship of thyroid hormones and lipid metabolism in hypothyroidism: A comprehensive review

Hypothyroidism is defined as a reduced activity of thyroid gland. It is due to the reduced secretion of either total thyroxine (T4) or triiodothyronine (T3). It causes increased secretion of thyroid stimulating hormone (TSH) and so significant increase in serum TSH levels.Hypothyroidism can be classified as primary (due to thyroid hormone deficiency), secondary (due to TSH deficiency), tertiary (due to thyrotropin-releasing hormone deficiency), and peripheral (extra-thyroidal; panel). The clinical expression of hypothyroidism range from life threatening—in the case of myxedema coma—to no signs or symptoms.Dyslipidemia seems to be common feature of hypothyroidism. The serum total cholesterol (TC), found to be elevated in hypothyroidism. It is also seen that triglycerides (TG) levels were also elevated in overt hypothyroidism but there is no significant increase in TG level in subclinical hypothyroidism. The HDL level is decreased only in patients of overt hypothyroidism but not in subclinical hypothyroidism. Hypothyroidism is also associated with increasing the risk of cardiovascular disorders.