The thyroid gland uses iodine (mostly available from the diet in foods such as seafood, bread, and salt) to produce thyroid hormones. The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3). While a small amount of T3 is actually made in the thyroid gland, most of it is converted in the tissues from the T4 released from the thyroid gland into the blood. T3 is the active hormone that affects the metabolism of cells.
Subclinical hypothyroidism is estimated to occur in a significant percentage of the adult American population (Hollowell JG et al 2002). One side effect of thyroid deficiency is high cholesterol. It is very possible that many people are being prescribed cholesterol-lowering statin drugs while their underlying problem—low thyroid function—goes unaddressed.
The most common cause of overt hypothyroidism in the United States is an autoimmune disorder known as Hashimoto’s thyroiditis (Lorini R et al 2003). This condition is characterized by an overactive immune system response that floods the thyroid gland with white blood cells that attack the gland. Hashimoto’s thyroiditis is more common in women than in men, and there is a genetic component to the disease.
There is evidence that the standard blood test reference ranges may cause many cases of hypothyroidism to be missed. (legs edit: big suprise!!) The standard reference range for TSH is between 0.2 and 5.5 mU/L. Any reading more than 5.5 mU/L would signal low thyroid hormone and possible hypothyroidism. Unfortunately, this TSH reference range is very broad. Many clinicians and scientists believe that the upper limit of the established “normal” range is too high to permit detection of people with significantly low thyroid function.
In reality, a TSH reading of more than 2.0 may indicate lower-than-optimal thyroid hormone levels.
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