it is very common to have normal TSH (Thyroid-Stimulating Hormone) and normal T4 levels on a lab blood test and yet to experience the devastating effects of insufficient thyroid hormones and a lack of tissue response at the cellular level.  With a Functional Medicine approach, I don’t dismiss how a patient feels, because normal test results might mask a problem with the larger picture of hormone transportation, conversion, connection, and positive impact.  (See Functional Medicine in the Menu.)

Sufficient thyroid hormone is essential for a healthy heart; brain development and function; muscle and nerve health; digestion and weight control; and bone maintenance. In the case of Hashimoto’s Disease, thyroid-replacement medication is necessary; however, there is no guarantee that any amount of synthetic or natural hormone in the blood is actually benefiting cells and tissues properly.  Every patient should be informed about the difference between serum (blood) thyroid hormone levels and cellular/tissue thyroid-hormone levels.

Summary of Parts I and II

Parts I and II explained how thyroid hormone in the blood can be blocked from attaching to thyroid-hormone receptor sites inside cells and, therefore, from alleviating low-thyroid symptoms.  The most common cause of receptor-site resistance may be the effect of cytokine immune messengers from Hashimoto’s Disease.  Autoimmune “attack” produce inflammatory cytokines, and inflammation blocks thyroid hormone from connecting with receptor sites.  Low levels of Vitamin D and Vitamin A will also result in receptor-site resistance.

In addition, too much cortisol, reverse T3, homocysteine, toxins and oxidative stress will block thyroid hormone from connecting with receptor sites.  Blood-sugar control, as well, has an impact.  Insulin resistance creates more inflammation, and so poor blood-sugar regulation ultimately blocks thyroid hormone from being useful.

Part II described conversion and enzyme problems.  Thyroid hormone must be converted from inactive T4 into active T3 to be used by cells, and this conversion in the body is largely dependent on an enzyme called D1 (or 5′-deiodinase).  Elevated cortisol from chemical, physical, emotional or mental stress suppresses D1 activity, so this minimizes the amount of thyroid hormone being converted into the active T3 form.  A person with a conversion problem will have low-thyroid symptoms, regardless of normal TSH and T4 serum levels on a lab blood test.

A high serum (blood) T4 level could mask a deeper problem: an insufficient amount of active T3 or cellular response at the tissue level, which results in low-thyroid symptoms.  High serum T4 levels would not trigger a rise in TSH, so this test would provide no clue to the possible hormone deficiency present in the body’s cells.  Only physical complications (hypothyroid symptoms) would signal a problem.  Clearly, when endocrinologists rely so much on TSH and T4 blood levels for thyroid wellness, a patient is not getting sufficient care.

A Broader Picture of What Can Go Wrong

If a person is taking thyroid-hormone medication, has normal TSH and T4 serum levels, and still has low-thyroid symptoms, there are one or more factors interfering with cellular/tissue thyroid health:

  1. a problem with transporting thyroid hormone to the liver and to other cells;
  2. a problem with inflammation, homocysteine, cortisol, reverse T3, toxins, Hashimoto’s cytokines, low Vitamin D, etc. blocking thyroid hormone from connecting with receptor sites inside cells;
  3. a problem with conversion of inactive T4 into active T3 (the useful form of thyroid hormone), often from poor blood-sugar control;
  4. a problem with damaged plasma membranes around cells because of nutrient deficiencies.

A plasma membrane surrounds each cell in the body.  Thyroid-hormone receptor sites are inside cells, so thyroid hormone must be able to reach these sites, to relieve low-thyroid symptoms.  Normally, membrane transporter proteins carry thyroid hormones across this plasma barrier, so that hormones can connect with their receptors inside cells.

If the cell’s membrane is damaged, though, transporters can’t do their job; and thyroid hormone circulating in the blood can’t enter cells and be useful.  This membrane gets damaged when there is a deficiency of Vitamin C, SAMe, and phosphatidylcholine.  There is also cell-membrane damage in people who have a genetic inability to turn folic acid into its active, useful form: folate.

Thyroid Medication Does Not Equal Thyroid Health

The cause of low-thyroid symptoms are many, and simply increasing the dosage of thyroid hormone could be a mistake.  it can, in fact, make the problem worse.  A patient can develop thyroid-hormone resistance, which means that receptor sites begin to shut down and do not take in enough thyroid hormone.  Also, excess T4 in the blood can turn into more reverse T3 (rT3), and reverse T3 lowers the amount of useful T3 available.  

On the other hand, an insufficient amount of thyroid medication might be prescribed if a doctor relies too heavily on the TSH level alone.  A normal TSH results, with hypothyroid symptoms, might point to a malfunctioning hypothalamus or pituitary gland.  The body needs more thyroid hormone, but either the hypothalamus or the pituitary isn’t responding to the need.  (Part I explained the brain’s role in balancing thyroid hormones.)

When a patient has low-thyroid symptoms but normal TSH and normal T4 serum levels, the problem might not be related to available thyroid hormone at all.  Persistent hypothyroid symptoms may be the result of adrenal exhaustion; a lack of sufficient sleep; a gut or a liver problem; a poor diet and poor blood-sugar regulation, as well as many other possibilities. 

Determining Cellular/Tissue Thyroid Levels

The goal for someone with low-thyroid symptoms is to have a normal response to the cell-receptor site and enough useful thyroid hormone in the body’s tissues.  In addition to considering the overall health of each patient, there are three tests that may help determine what the level of cellular/tissue thyroid hormone might be: 1) testing the amount of TBG (Thyroid Hormone Binding Globulin) present in the blood; 2) testing a patient’s Basal Metabolic Rate; and 3) testing Tendon Relaxation Speed.

As described in Part I, Thyroid Hormone Binding Globulin (TBG) is a protein made in the liver.  It transports thyroid hormones (T4 and T3) to the liver and to every cell in the body. Elevated estrogen and oral contraceptives can increase TBG, which results in low Free T4 and low usable, active Free T3 thyroid hormone at the cellular level; therefore, too much TBG is a cause of low-thyroid symptoms.

Hypothyroidism and elevated testosterone may result in decreased TBG.  If a patient is taking thyroid-hormone medication and TBG is insufficient, it’s possible that not enough thyroid hormone is being transported to tissues.  An insufficient amount of TBG may also result in too much unbound (Free) T3 in the blood, which is as problematic as not having enough. With too much serum Free T3, thyroid-hormone receptor sites become less “sensitive,” and the patient will experience low-thyroid symptoms.

Due to the fact that thyroid hormones have a stimulating effect on metabolic activities in body tissues, the Basal Metabolic Rate is increased.  Measuring the BMR is a clue to a patient’s tissue thyroid levels, as opposed to just how much thyroid hormone is circulating in the blood.

Tendon Relaxation Speed provides another clue to hypothyroid tissue levels.  In this test, the Achilles tendon is tapped in a brisk way, and the rate that the calf muscle relaxes corresponds to thyroid function.  A slow response is typical of a muscle affected by hypothyroidism.  When muscles and nerves are benefiting from enough thyroid hormone, there should be an immediate response that is loose and floppy.

A Functional Medicine Consultation

Though lab testing for serum TSH and T4 levels are helpful, results that fall in a normal range do not confirm that a sufficient amount of useful thyroid hormone is benefiting the body’s tissues.  As a Functional Medicine doctor, I educate my patients; test for overall health; and listen carefully to patients with ongoing symptoms.  

For a free, 15-minute phone consultation with me, Dr. Steven Roach, schedule on our Contact Us page or call (704) 853-8000.