The Thyroid and Thyroid Hormones

by Nikolas Hedberg, D.C., D.A.B.C.I. on February 8, 2011

The thyroid is a small gland that lies in the neck about the level of the Adam’s apple and weighs approximately one ounce.  It produces thyroid hormone and calcitonin.  The parathyroid glands are very small and lie on the outside portion of the thyroid gland and secrete parathyroid hormone.  We will be focusing on thyroid hormone.
 
The thyroid gland is stimulated to make thyroid hormone by thyroid-stimulating hormone (TSH) which is produced in the pituitary gland located in the brain.  The pituitary is controlled by the hypothalamus in the brain which monitors the amount of circulating thyroid hormone.  Iodine must enter the thyroid gland through a transport system that is repaired with the intake of vitamin C.  There is usually about 20-30 mg of iodine in the body and 75 percent of it is stored in the thyroid.  In addition to iodine, magnesium, zinc, copper, and vitamins B2, B3, and B6 are required for thyroid hormone production.

The thyroid gland produces two thyroid hormones: T4 (thyroxine) and T3 (triiodothyronine).  Ninety-five percent of thyroid hormone produced is T4 and five percent is T3.  T3 is the active form of thyroid hormone which is produced as a result of one iodine being cleaved from T4.  T4 is inactive so the majority of thyroid hormone produced is actually inactive.  The numbers “3” and “4” indicate the number of iodines.  This is key in understanding optimal thyroid function.  Both T4 and T3 are bound to proteins in the blood until they reach your cells and become unbound to work their magic on metabolism. 

Most of the T4 is converted into T3 in the liver.  Approximately sixty percent of the T4 is converted into T3, twenty percent is converted into an inactive form of thyroid hormone known as reverse T3 (irreversible), and the remaining twenty percent is converted into T3S (T3 sulfate) and T3AC (triiodothyroacetic acid).

Conversion of T4 hormone

Reverse T3 can be problematic; even though it is inactive, it will still bind to T3 receptors and block T3 from binding and working its magic on metabolism.  Too much or too little cortisol that is produced by the adrenal glands will increase circulating levels of reverse T3.  This mechanism is due to suppressed liver detoxification and clearance of reverse T3 from excess cortisol production.  Stress can not only cause signs of hypothyroidism but it will also impair the liver’s ability to detoxify.  Cortisol will also suppress TSH production resulting in low thyroid function.  Immune system activation, high adrenaline, excess free radicals, aging, fasting, stress, prolonged illness, and diabetes will also drive the inactivation of T3 to reverse T3.

Reverse T3

T3 and reverse T3 can also be inactivated by conversion into a hormone known as T2.  Elevated insulin levels due to a diet high in refined carbohydrates will also increase reverse T3 levels.  Toxic metals including mercury, cadmium and lead will also increase reverse T3 production.  T3S and T3AC are inactive until they are catalyzed by an enzyme in the GI tract known as sulfatase.  This enzyme is dependent on healthy gut bacteria.  We will discuss in a later chapter the importance of a healthy digestive tract as it relates to twenty percent of active thyroid hormone.

Thyroid hormone’s main role is to control metabolism (energy production) inside the cell.  Our cells contain tiny factories called mitochondria that produce energy from fat, sugar and protein.  Thyroid hormone controls the function of the mitochondria which determines how much energy is produced.  Symptoms of low thyroid function are related to a decrease in energy production including:

  • Fatigue
  • Weight gain/inability to lose weight
  • Constipation
  • Dry/itchy skin
  • Dry brittle hair and nails
  • Depression
  • Headaches
  • Overly sensitive to cold
  • Cold/numb hands and feet
  • Muscle cramps
  • Depressed immune system–can’t recover from infections
  • Slow wound healing
  • Unrefreshing sleep
  • Digestive problems due to low stomach acid
  • Hair falls out
  • Water retention
  • Lateral third of eyebrow thinning

Thyroid-Stimulating Hormone (TSH)

Traditional medicine relies mainly on the TSH or thyroid-stimulating hormone blood  test to measure thyroid function.  TSH is not a thyroid hormone.  TSH is produced by the pituitary based on how much thyroid hormone is circulating in the bloodstream.  As thyroid hormone levels drop, TSH production will increase to stimulate the thyroid to make more hormone.  If thyroid hormone increases, then TSH production will decrease because the thyroid is making plenty of hormone.  The TSH alone is not adequate to assess thyroid function because it doesn’t take into consideration the conversion of thyroid hormone into its active form which occurs in the liver, kidneys and lungs.  The TSH test also does not take into account thyroid hormone receptor resistance.  Thyroid hormone receptors can become resistant to thyroid hormone due to thyroid-disrupting chemical exposure leading to normal blood tests but development of low thyroid symptoms.  Cortisol produced during stress by the adrenal gland can also inhibit TSH production further throwing off the accuracy of the test.  If the TSH is elevated, the traditional physician will prescribe synthetic T4 and this will usually reduce TSH into the “normal” range.  This approach does not take into account peripheral thyroid hormone conversion or receptor binding.  If the body is compromised in its ability to activate thyroid hormone into T3, then taking T4 will result in a failure of treatment.  If the adrenal glands are out of balance, then most likely thyroid hormone function will also be out of balance.  In addition, if thyroid hormone receptors are desensitized, this approach will fail as well.

You will find that most medical physicians do not spend much time reading the peer-reviewed medical literature which provides us with valuable data on TSH levels.  An excellent study was published by Obal and Krueger (2001) on sleep deprivation and thyroid hormone production.  The researchers concluded:  “When sleep deprivation is maintained for weeks, the plasma concentrations of T4 and particularly T3 decline but TSH remains normal.”6  Do physicians ask you about your sleep patterns?  Perhaps this could be the reason for the abnormal TSH.  I have seen many patients who also suffer from insomnia and sleep problems and present with low thyroid symptoms and abnormal TSH levels.  Does this mean they should have thyroid hormone dumped into their bodies?  Unfortunately, this happens to many people.  I always take into account every patient’s sleep pattern and correct it as part of our treatment plan.  Many times, sleep patterns are abnormal due to blood sugar and adrenal gland imbalances.  Remember, you are not a lab test but a beautiful, complex being where everything is connected as one. 

Testing & Diagnosis

Blood tests alone cannot always adequately diagnose thyroid hormone imbalance.  It is estimated that about forty percent of the U.S. population suffers from some kind of thyroid imbalance as opposed to the current traditional figure of ten percent.  This is due to the inadequacies of the TSH test.  In addition to blood testing, I review a thorough case history and a number of detailed health questionnaires and also perform a comprehensive physical examination for clues to thyroid hormone imbalance.  Basal body temperature testing is used by many practitioners to evaluate thyroid function but this does not solely indicate a thyroid imbalance.  There are many other factors that can cause a low basal body temperature such as adrenal fatigue, leaky gut, impaired liver detoxification and malnutrition.  I use the basal body temperature simply as one more diagnostic tool to evaluate the overall picture of a patient.  Another sign that may indicate low thyroid function is thinning of the lateral one-third of the eyebrow.

The following thyroid tests can provide more information about your thyroid.  Use this as a guide when you get the results of your blood tests:

  • TSH (Thyrotropin) – Thyroid-stimulating hormone is produced by the pituitary to stimulate the thyroid to make hormone.  The ideal range is 1.8-3.0.  Traditional medicine uses a much broader range of 0.5-5.5.  This range misses many hypothyroid patients such as those with a TSH between 3.0-5.5. 
  • Total Thyroxine (T4) – This test measures the amount of T4 (thyroxine) that is both bound to protein and unbound.
  • Free Thyroxine Index – This is calculated by multiplying the TT4 by the T3 uptake.  The result gives you the amount of unbound T4 or Free T4.
  • Free Thyroxine (Free T4) – This measures the amount of unbound or free T4 which is the most active form.  Free T4 is not affected by medications or other factors that affect protein bound thyroxine (TT4).
  • T3 Uptake – A measurement of the amount of available binding sites for free T3 on thyroxine-binding proteins.  Elevated testosterone will reduce the number of binding sites and cause a low T4 and high T3 uptake.  Excess estrogen from hormone replacement or birth control pills will increase binding sites and can cause high T4 and low T3 uptake.
  • Free Triiodothyronine (Free T3) – This is a measure of free T3 levels or unbound T3.  This is the best test if your natural physician wants to see the amount of available active thyroid hormone in the bloodstream.
  • Reverse T3 (rT3) – This is a measurement of the amount of T3 that has been inactivated.
  • Thyroid Antibodies – Thyroid peroxidase, thyroid-stimulating immunoglobulin and antithyroglobulin elevations indicate autoimmune thyroid disease such as Hashimoto’s or Graves’ disease.  Thyroglobulin and calcitonin are mainly used in the diagnosis of more serious thyroid diseases such as cancer.

Prescription Medications

Prescription medications do not take into account underlying physiological imbalances and may lead to dependence on the medication.  The following drugs are prescribed by physicians to treat the thyroid:

  • Synthroid – Synthetic thyroxine (T4).  Synthroid is the most popular prescription drug for hypothyroidism.  Synthroid is in the top five most commonly prescribed drugs in the US.  Synthroid can be converted incorrectly into inactive reverse T3 resulting in no symptom improvement. Synthroid depletes calcium for bones and may not provide improvement for patients who have compromised conversion pathways of T4 into T3 or any of the other imbalances described in this book.   
  • Levoxyl – Synthetic thyroxine (T4).
  • Levothroid –  Synthetic thyroxine (T4).
  • Levothyroxine – Synthetic thyroxine (T4).
  • Thyrolar – Synthetic T4 and T3.
  • Cytomel – Synthetic T3.  Many side effects including hyperthyroid symptoms.
  • Armour Thyroid, Nature Thyroid, Westhroid – Natural thyroid hormone from desiccated pig thyroid tissue.  Contains approximately 38 micrograms/grain of T4 and 9 micrograms of T3/grain as well as other cofactors for thyroid hormone production.  Nature Thyroid is a better choice than Armour because it does not contain corn and other binders.

Many alternative-minded medical doctors prescribe Armour and other natural dessicated pig thyroid tissue.  This is a better option in some cases than merely prescribing synthetic T4 (Synthroid) because these natural agents also contain T3.  The problem with Armour is that it contains corn and other fillers which can be a problem for those with specific sensitivities.  Nature Thyroid is the best choice because it doesn’t contain corn or fillers.  But the author does not agree with this treatment method because even though it is a better option, it still does not take into account the underlying causes of why the thyroid is out of balance in the first place.  These natural prescriptions still only replace thyroid hormone and require dependence on the doctor for continued prescriptions and office visits.  I have seen many, many patients who are on such natural prescriptions who still have many symptoms and have been taking the prescription for a long period of time.  Even if someone responds to a prescription such as Armour thyroid, she should be rigorously evaluated for underlying physiological imbalances.

Another issue with such treatment methods is suppression of hypothalamic-pituitary-thyroid feedback mechanisms.  Whenever you take a hormone that is produced in the body, this tells the brain that it no longer needs to stimulate hormone production because it is constantly being ingested.  When male bodybuilders take testosterone, their testicles shrink because there is no longer a need for them to make testosterone.  Taking thyroid hormone for long periods of time will suppress natural production which may or may not return after discontinuing the medication.  It is strongly encouraged that you do everything possible to normalize thyroid function before going on medication of any kind.  Americans typically want a quick fix, a magic pill that will instantly give relief.  Many people get this instant relief from medication but the long-term effects of dependency and suppression of natural hormone production may not be worth it.    Patients who have had their thyroid removed or partially removed may require prescription thyroid hormone.  If the gland is not present then thyroid hormone must be replaced.  In this case, prescriptions such as Armour and Nature Thyroid are the better choice.

Conversion of T4 into T3

T3 is much more active than T4 and is responsible for most of the actions of thyroid hormone on the cell.  Some people cannot convert T4 into T3 as efficiently as others.  In addition, there are many factors that could be inhibiting this process.

Selenium, antioxidants, iron, magnesium, zinc, vitamin A, vitamin B6 and B12 deficiencies can lead to poor conversion.  The medications listed above affect thyroid hormone conversion as well as production and receptor binding.  As people get older, they lose their ability to convert thyroid hormone which may be due to decreased vitamin and mineral absorption.  This is due to a loss of intestinal barrier function where all of your nutrition is absorbed.  This barrier loses its function as we age so supplementation is absolutely necessary.  Excess estrogen from xenoestrogens in the environment, birth control pills and hormone replacement can lead to low thyroid symptoms.  Estrogen increases the protein that binds to thyroid hormone leaving excess thyroid hormone bound to protein which is inactive until it becomes unbound.  Cortisol produced by the adrenal gland is a major factor in converting thyroid hormone.  Too much cortisol can inhibit the activation of thyroid hormone and too little cortisol yields the same result.  Exhausted adrenals will cause low thyroid symptoms due to the lack of cortisol production.  Insulin is a hormone released by the pancreas to handle blood sugar elevations after consumption of carbohydrates and can inhibit hormone conversion as well.  Soy products have been shown to inhibit the conversion of thyroid hormone.  This only goes for soy products that are non-fermented.  Fermented soy products such as miso and tempeh are okay. 

Vitamin C has been shown to enhance the conversion of thyroid hormone.  Radiation, chemotherapy, growth hormone deficiency, and cigarette smoke have also been shown to reduce thyroid hormone conversion.  We will get into more detail of how these imbalances can affect thyroid hormone function and production in each chapter.

 

Previous post:

Next post: