Thyroid hormone replacement has been used for more than a century to treat hypothyroidism. Natural thyroid preparations (thyroid extract, desiccated thyroid, or thyroglobulin), which contain both thyroxine (T4) and triiodothyronine (T3), were the first pharmacologic treatments available and dominated the market for the better part of the 20th century. Dosages were adjusted to resolve symptoms and to normalize the basal metabolic rate and/or serum protein-bound iodine level, but thyrotoxic adverse effects were not uncommon. Two major developments in the 1970s led to a transition in clinical practice: 1) The development of the serum thyroid-stimulating hormone (TSH) radioimmunoassay led to the discovery that many patients were overtreated, resulting in a dramatic reduction in thyroid hormone replacement dosage, and 2) the identification of peripheral deiodinase-mediated T4-to-T3 conversion provided a physiologic means to justify l-thyroxine monotherapy, obviating concerns about inconsistencies with desiccated thyroid. Thereafter, l-thyroxine mono-therapy at doses to normalize the serum TSH became the standard of care. Since then, a subgroup of thyroid hormone–treated patients with residual symptoms of hypothyroidism despite normalization of the serum TSH has been identified. This has brought into question the inability of l-thyroxine monotherapy to universally normalize serum T3 levels. New research suggests mechanisms for the inadequacies of l-thyroxine monotherapy and highlights the possible role for personalized medicine based on deiodinase polymorphisms. Understanding the historical events that affected clinical practice trends provides invaluable insight into formulation of an approach to help all patients achieve clinical and biochemical euthyroidism.

Heart problems - Hypothyroidism may be associated with increased risk of heart disease, mainly because high levels of low-density lipoprotein cholesterol (“bad” cholesterol) may occur in patients that have an underactive thyroid. Even mild or early stage hypothyroidism that does not present symptoms can cause an increase in total cholesterol levels and diminish the heart’s ability to pump blood.


Having a thyroid condition is no picnic, but you're not alone with this health issue. According to the American Thyroid Association, more than 12 percent of the population may end up dealing with a thyroid condition at some point in their lives. And thyroid issues can be sneaky: Of the nearly 20 million Americans living with the disease, as many as 60 percent don't even realize they have it.

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