What Your Doctor May Not Tell You About Your Thyroid Hormones

By John R. Lee, M.D.
From the John R. Lee, M.D. Medical Letter – November 2000

A Deficiency May Not Show Up on a Standard Thyroid Test

It’s time to talk again about thyroid problems. Thyroid hormone is now the most common of all drug prescriptions, though estrogen sales may still be the most profitable.

The premise of thyroid is simple—the thyroid gland makes thyroid hormones that set the metabolic rate (the rate at which energy is used) for all the cells of the body. Thyroid hormone is said to be the throttle, or gas pedal, or governor for all metabolic activity. All first year medical students get that right. Then they learn that there is a computer in the hypothalamus gland in the brain that monitors and modulates thyroid hormone levels to control metabolic activity. This computer makes a hormone called thyrotropin releasing hormone (TRH), that signals the pituitary gland in the brain to make another hormone, thyroid stimulating hormone (TSH) (also called thyrotropin) that instructs the thyroid gland to make more or less thyroid hormone for circulation throughout the body. This sets the body’s metabolic rate. If the hypothalamic computer detects a lagging metabolic rate, it signals the pituitary to make more TSH, which activates the thyroid gland to make more thyroid hormone. If the metabolic rate is too high, it reduces TSH to slow the production of thyroid hormone. What a beautiful system! A low TSH reading may indicate high thyroid levels, while a high reading may indicate low thyroid levels.

But then things get a bit more complicated. One would think that by measuring the thyroid level in the blood stream, or the level of TSH, or TRH (a more difficult test), one could easily determine whether thyroid hormone supplementation was necessary. As it turns out, the “normal” range is broad. Just because your thyroid level is in the “normal” range, that does not mean that all is well with your thyroid or metabolic regulation. What is normal for one individual may not be normal for another. If someone is lacking energy, or cold all the time, or not feeling up to par, (all symptoms of hypothyroidism—low levels of thyroid hormone), perhaps the cause is merely lack of sleep, the need for a vacation, or bad diet, stress, or some nutrient deficiency. If we succumb to the erroneous belief that “normal” thyroid tests rule out thyroid problems, there are plenty of other suspects to consider, and the potential thyroid problem is ignored.

The Basics on T3 and T4

Here’s a closer look at how thyroid hormone really works. Thyroid hormone is a remarkably simple compound, made of a single amino acid (protein) called tyrosine plus the addition of some iodine atoms. Actually, the thyroid gland makes two thyroid hormones, thyroxine (with 4 iodines) and triiodothyronine (with 3 iodines). In medical parlance, thyroxine is called T4, and thyronine is called T3, indicating the number of iodines in each molecule.

Thyroxine blood levels are higher than that of thyronine, but thyronine is four times more potent. Normally the body converts T4 to T3 as needed. The total thyroid effect is a combination of both T4 and T3. Though not common in conventional medicine, ideal thyroid replacement therapy should consider the use of both T4 and T3. The most commonly prescribed thyroid medication is Synthroid (Editor’s Note: Synthroid is also known by its generic name, Levothyroxine), which is only T4. Armour thyroid is derived from cows, sheep, and/or pigs, and contains whole ground-up thyroid gland; it is standardized to deliver both types of thyroid hormone in the same ratio found in human thyroid.

What Thyroid Hormone Does

Thyroid hormone increases the number and activity of mitochondria, those little intracellular inclusions (they exist separately from the cell but are found inside the cell) that convert food we eat (particularly carbohydrates) into energy for the body. Thyroid increases protein synthesis (for growth and repair), excites the nervous system (for alertness and quicker reflexes), and stimulates the endocrine system in general. Thyroid hormone is metabolized much more slowly than other hormones; traces of a single dose can still be detected a month later. However, thyroid supplements must be taken daily to maintain thyroid hormone levels.

Thyroid deficiency can cause an amazing variety of symptoms. A brief list of symptoms includes general fatigue, feeling more chilly than most people, difficulty in losing weight, muscle aches and pains, mental sluggishness, dry skin, dry hair and hair loss, waking up tired, anxieties and/or depression, increased menopausal symptoms, slow pulse, and digestive problems. Each of these symptoms might well be caused by something else but when enough of the whole set is present, it is wise to think of hypothyroidism. People with underactive thyroids also show an increased tendency for auto-immune disorders.

Low thyroid can intensify the ill effects of other diseases because all metabolic actions require energy, and thyroid hormone sets the energy level. If thyroid is low, your energy is low and your body is less able to deal with other conditions. Examples are chronic stress, poor sleep, colds and other viral or bacterial infections, malnutrition, anemia, injuries or surgery. Without good thyroid levels, recovery is delayed.

Potential Causes of Hypothyroidism

Why should thyroid deficiency be so common now? Historically, iodine deficiency was the most common cause of hypothyroidism and goiter (enlarged thyroid gland). Without sufficient iodine, thyroid hormone production results in thyroxine being stored in the gland rather than being released into the circulation. This leads to engorgement of the gland, causing goiters. The condition was most prevalent in populations that did not live near the sea, because all ocean fish, crustaceans, and seaweed contain iodine. Now that iodine is added to salt, and seafood is widely available, iodine deficiency is not as common. Our present epidemic of thyroid problems is not due to iodine deficiency. We must look elsewhere.

The Estrogen Dominance Factor

No hormone works in isolation from other hormones; they all function within a complex, subtle web of interconnectedness. If thyroid is low, cortisol and sex hormone production lags. For example, estrogen inhibits thyroid hormone activity, and thus exacerbates thyroid deficiency. In contrast, progesterone and testosterone are thyroid allies. I have written about this in detail in a past newsletter (March 1999). Clinical judgement must include consideration of the balance of different hormones.

The Autoimmune Factor

The immune system is also a major factor in hypothyroidism. In particular, anti-thyroid antibody disease (Hashimoto’s thyroiditis), once considered rare, is now a common finding, especially among women. The antibody attack on the thyroid causes chaos in the hormone cycle. It may provoke hyperthyroidism (elevated T4 levels or excess thyroid) or classic hypothyroidism (low T4 levels). Since the cause is usually unknown, conventional treatment consists of thyroid supplementation sufficient to drive TSH to very low levels, thus effectively stopping endogenous (made in the body) thyroid hormone synthesis.

The Fluoride Factor

The thyroid molecule is simply a thyronine molecule with some iodines attached. Thyroid only works if iodine is attached there. Iodine is a halogen, a group of non-metallic elements that also includes fluorine, chlorine, and bromine. If you look at the periodic table of elements, you note that they all are short by one electron of having a complete outer ring of electrons. They all seek to acquire an extra electron. In chemical reactions, a more reactive halogen will replace a less reactive halogen. Iodine is the largest of the four common halogens and its chemical activity is the least among them, whereas fluorine is the smallest of the halogens and is the most chemically active.

In the past two generations, fluoride exposure has increased greatly due to fluoridated water and toothpaste. Prior to fluoridation, the common daily intake of fluoride was about 0.1 mg/day. Now, fluoride intake even in unfluoridated communities is 30 to 40 times greater. If fluorine replaces iodine in the structure of thyroxine, it would make it unsuitable for thyroid hormone effect. Years ago, fluoride was used to treat hyperthyroidism. Why is this fluoride poisoning now ignored? Not only is fluoridated tyrosine unsuitable for thyroxine construction, but it may stimulate antibody formation, leading to thyroiditis.

Thyroid and Endocrine Disrupters

Many petrochemical toxins are also known as endocrine disrupters. In the case of thyroid, a plausible mechanism for damage is known. Look again at the thyroxine molecule. Note its two phenol rings connected by an oxygen atom. This is remarkably similar to the structure of polychlorinated biphenyls (PCBs), widespread industrial pollutants which are not only estrogenic but also toxic to the thyroid gland itself.

The development of the inner ear in human embryos requires thyroid hormone. If exposed to PCBs, the cochlear development is inhibited, causing low tone hearing loss. Animals exposed to PCBs develop thyroid tumors, now common in cats, for instance. It is entirely possible that the chlorinated biphenyls are perceived by the immune system as abnormal thyroxine. In the process, one’s antibodies attack the thyroid gland. Thus, industrial pollutants known as PCBs or other similar petrochemical endocrine (hormone) blockers may be a major cause of hypothyroidism caused by thyroiditis.

Smart doctors know about thyroid testing. Wise doctors know that conventional tests are often inadequate for diagnosing and treating patients with hypothyroidism. Hypothyroidism is more complex than generally realized. Attention must be directed to identifying and removing the cause or conditions rather than only treating symptoms.