Hypothyroid disease may be due to a number of causes, including poor adrenal function,
environmental toxicity, inadequate nutrition, autoimmune disease, and genetic predisposition.
Prolonged treatment with superphysiological doses of corticosteroids such as
prednisone can also lower thyroid function [Starr2005, pg 158].
Starr has identified two types of hypothyroid disease, which he refers to as
Type I and Type II. In analogy with Diabetes Types I and II,
Hypothyroidism Type I is due to a failure of the thyroid gland to produce adequate thyroid
hormone, while Hypothyroidism Type II is attributed to cellular resistance to circulating
thyroid hormone [Starr2005].
There are many causes for inadequate thyroid hormone being produced,
which may result from a failure of the hypothalamus to produce Thyroid Releasing Hormone (TRH),
failure of the pituitary to produce Thyroid Stimulating Hormone (TSH),
failure of the thyroid gland to produce T4, or failure of the liver and kidneys to convert
the T4 to the most active form of the thyroid hormone, T3. In some cases the peripheral
tissues convert T4 to an inactive form called reverse-T3. Blood tests can help identify
the nature of these failures in Type I Hypothyroidism.
On the other hand, when hypothyroidism is due to lack of cellular response to adequate levels
of T3 (i.e. Type II Hypothyroidism), blood tests may appear to be normal and the diagnosis
must be made based on signs and symptoms [Starr2005].
Some practitioners have noted an association with
inflammatory process mediated by homocysteine [Rogers2008, pg 9]. Note that the common
diuretic hydrochlorothiazide (HCTZ) increases homocysteine levels [Westphal2003].