Until a little more than one hundred years ago, the single controlling force for all of the complex processes  that go on in the human body was    thought to be the nervous system. But there were too many phenomena  that, when carefully analyzed, seemed to have no relationship to the nervous  system, too many differences    in people--in size and energy, for example--that could not be accounted for satisfactorily in terms of nervous  activity  alone. The explanation was to be found in certain glands, the endocrines, of which the thyroid is  one and, in fact, one of the first to be discovered.  Because commonly used tests for thyroid function are not accurate particularly when it comes to mild and even some moderate forms of  hypothyroidism, and many if not most of those with low thyroid function remain undiscovered.
 

 Since the hormones of the thyroid gland regulate metabolism in every cell of the body, a deficiency of thyroid hormones can affect virtually all bodily  functions. The degree of severity of symptoms in the adult range from mild deficiency states which are not detectable with standard blood tests  (subclinical hypothyroidism) to severe deficiency states which can be life-threatening (myxedema). There is an old medical saying that just a few  grains of thyroid hormone can make the difference between an idiot and an Einstein. It aptly characterizes the thyroid as a quickener of the tempo of    life. All of the endocrine glands play remarkable roles in the body's economy. Unlike the many millions of other glands such as the sweat glands in  the skin, the salivary glands in the mouth, the tear glands in the eyes, which perform only local functions, the endocrine glands pour their hormone secretions into the bloodstream which carries them to all parts of the body. From the pea-sized pituitary gland at the base of the brain come hormones that influence growth, sexual development, uterine contraction in childbirth, and milk release afterward. The adrenals, rising like mushrooms from atop the kidneys, pour out more than a score of hormones, including hydrocortisone and adrenaline needed for the body's response to stress and injury. Also in the endocrine system are the sex glands—ovaries and testes; the pineal gland in the brain whose hormones play a role in nerve and brain functioning; the thymus behind the breastbone which appears to be involved in establishing the body's immunity function; and areas in the pancreas, the islets of Langerhans, which secrete insulin.


A large majority of the thyroid hormone secreted from the thyroid gland is T4, but T3 is the considerably more active hormone. Although some T3 is also secreted, the bulk of the T3 is derived by deiodination of T4 in peripheral tissues, by the enzyme thyroid peroxidase especially liver and kidney. Deiodination of T4 also yields reverse T3, a molecule with no known metabolic activity. Deficiency of thyroid hormone may be due to lack of stimulation by the pituitary gland, defective hormone synthesis or impaired cellular conversion of T4 to T3 (often caused by mercury toxicity). The pituitary gland regulates thyroid activity through the secretion of thyroid-stimulating hormone (TSH). The combination of low thyroid hormone and elevated TSH blood levels usually indicates defective thyroid hormone synthesis, which is defined as primary hypothyroidism. When TSH and thyroid hormone levels are both low, the pituitary gland is responsible for the low thyroid function, a situation termed secondary hypothyroidism. Normal blood thyroid hormone and TSH blood levels combined with low functional thyroid activity (as defined by a low basal metabolic rate) suggest cellular hypothyroidism.


Most estimates on the rate of hypothyroidism are based on the levels of thyroid hormones in the blood. This may result in a large number of people with mild hypothyroidism going undetected. Before the use of blood measurements, it was common to diagnose hypothyroidism based on basal body temperature (the temperature of the body at rest) and Achilles reflex time (reflexes are slowed in hypothyroidism). With the advent of sophisticated laboratory measurement of thyroid hormones in the blood, these "functional" tests of thyroid function fell by the wayside. However, it is known that the routine blood tests may not be sensitive enough to diagnose milder forms of hypothyroidism. The diagnosis of hypothyroidism by laboratory methods is primarily based on the results of total T4, free T4, T3, and TSH levels. The typical blood tests measure thyroxine (T4), which accounts for 90% of the hormone secretion by the thyroid. However, the form that affects the cells the most is T3 (triiodothyronine) which cells make from T4. If the cells are not able to convert T4 to the four-times more active T3, a person can have normal levels of thyroid hormone in the blood, yet be thyroid-deficient.


The enzyme thyroid peroxidase, converts T4 to T3 and is blocked by mercury in the body, primarily from dental mercury amalgam fillings and thimerosol, a mercury preservative found in vaccinations and other medicines. Genistein and daidzein from soy also inactivate thyroid peroxidase enzyme. In the case of T4 and T3, more than 99% is normally protein-bound in the blood. Less than 1% is free. Only the free hormone exerts biologic activity. The protein-bound hormone is inactive. The saliva test is a more accurate and sensitive way to assess thyroid function because new technology allows for direct measurement of the free thyroid hormones.


A better way of assessing thyroid function is to measure its effects on the body. This is done by measuring a person's resting metabolic rate, which is controlled by the thyroid gland. Dr. Broda Barnes found that measuring basal body temperature (description follows) was a good way of assessing basal metabolic rate (BMR) and thus the body's response to thyroid hormones, regardless of their blood levels. As mild hypothyroidism is the most common form of hypothyroidism, many people with hypothyroidism are going undiagnosed. The basal body temperature is the most sensitive functional test of thyroid function. Nonetheless, using blood levels of thyroid hormones as the criteria, it is estimated that between 1 and 4% of the adult population have moderate to severe hypothyroidism, and another 10-12% have mild hypothyroidism. The rate of hypothyroidism increases steadily with advancing age. Using only blood tests, thyroid function is commonly low in older adults. When using medical history, physical examination, and basal body temperatures along with the blood thyroid levels as the diagnostic criteria, estimated rates of hypothyroidism approach 90% or more of the adult population. (...)

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