Dr. Matthew Buckley
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Thyroid Dysfunction

5 Ways in which the gut can cause thyroid dysfunction.

  ai Fatigue/Chronic Fatigue SyndromeThe relevance to Hippocrates, the father of medicines statement, “All disease begins in the gut.” is perhaps most clearly understood when you examine the relationship of the gut to thyroid function.  The reason for this is because without a healthy gut the ability to produce active thyroid hormone is impaired, and low active thyroid hormone (free T3) cellular response negatively effects every cell in the body therefore contributing to every health challenge if it’s at less than optimal function.  What is most commonly assessed and treated medically related to thyroid function is primarily based on TSH and T4 blood levels.  Unfortunately, these markers do NOT totally account for the response to your bodies active thyroid hormone ( free T3).  In other words, having abnormal thyroid function is COMMON even though lab tests are “normal” with or without thyroid medication!  What does thyroid hormone dysfunction cause?  Here’s a brief list:

Thyroid Dysfunction Symptoms


  • Brain Fog
  • High Cholesterol
  • Heart Disease
  • Constipation
  • Dry Skin
  • Frequently Feeling Cold
  • Hair Loss
  • Low Libido
  • Depression
  • Irregular Menstrual Cycle
  • Muscle Aches/Fibromyalgia
  • Joint Pain
  • Poor Immunity
  • Weight Gain
  • Inability to Lose Weight Even With Exercise

What is the thyroid gland, and what does it produce?  The thyroid is a small butterfly shaped gland sitting at the lower portion of the trachea. Upon receiving the call to produce thyroid hormone from the pituitary hormone TSH, the thyroid gland releases two hormones – T4 (93%), and T3 (7%).  Remember, only T3 is active to the cells, and of the total amount of thyroid hormone produced by the thyroid gland itself, only 7% is in its active form.  Additionally, the thyroid gland also produces the hormone calcitonin, which is important for transferring calcium into bones.  The 93% of the largely inactive T4 is left to travel to the liver and to the intestines to become activated.  Within the liver the T4 undergoes a conversion process that can either convert T4 into the active T3, or it can convert it into something called reverse T3 (rT3).  Under normal circumstances 60% of T4 will convert to T3, 20% to rT3, leaving the remaining 20% to be activated in the small intestine.  It’s in this conversion process here that accounts for many functional thyroid disorders.  Functional thyroid disorders are distinctive from conditions where TSH and T4 move into pathological (disease state) ranges which require medical treatment.  Rather, functional thyroid disorders include all dysfunction of thyroid production and cellular response with or without reaching pathological levels in TSH or T4 blood levels. What about thyroid medications?  The most commonly prescribed thyroid medications (Synthroid, Levothyroxine, or Levoxyl) are synthetic versions of T4.  These medications rely upon proper conversion in the gut – which as you’ll see below does not happen efficiently for many people on or off medications.  When assessing the success of treatment of these medications, it’s primarily the lab values of TSH and T4 that the doctor is paying attention to – not whether or not the active thyroid hormone is being produced and is effectively entering the cells of the body.  Natural thyroid hormones in the form of Armour Thyroid or Nature-Throid, are glandular preparations of thyroid hormone that contain T4,T3, and calcitonin.  For some people these natural versions seem to perform better, but because some people have problems with overconversion from T4 into rT3 for reasons listed below, these meds may be ineffective too. Below are 5 ways in which the alterations in the gut may result in abnormal thyroid hormone function.  (The liver serves many functions, and one of them is bile production and for this reason it is included as a component of the gut.)

  1. Hashimoto’s disease–  Hashimoto’s disease is the name given to autoimmune disease of the thyroid gland, where the immune system attacks cells of the thyroid gland.  Hashimoto’s disease is estimated to be the most prevalent autoimmune disorder in the US.  Hashimoto’s has been found to be the mechanism for hypothyroidism in 90% of the cases in the US.  One of the primary mechanisms for auto-immune disorders is “leaky gut”, where the gut lining becomes damaged and allows material (pathogens, undigested food, etc.) to cross the gut barrier and into the blood that was not supposed to cross.  If “leaky gut” contributes to autoimmune disease in general, and it’s recognized that most cases of hypothyroidism are the result of an autoimmune condition, it’s reasonable to assume that the gut may be involved in most cases of hypothyroidism.
  2. Gluten sensitivity– This could be grouped in with Hashimoto’s since it’s typically associated with autoimmune disorders, but is separate because gluten is a unique agent in autoimmune hypothyroidism.  Gluten is a protein found in the grains – wheat, barley, rye, and oats.  It is believed that the gluten molecule appears similar to the cells of the thyroid, so if the body identifies gluten as a problem it may identify the thyroid as a problem as well. So, if 90% of the cases of hyopthyroidism are from an autoimmune condition, and  gluten sensitivity is linked to a high degree of autoimmune thyroid disorders- avoiding gluten is important for a number of reasons, but especially important for anyone with a suspected thyroid disorder. Here are a few studies linking the connection between gluten and thyroid dysfunction:  (1), (2), (3), (4).  Keep in mind, that even if you tested negative for celiac disease there’s still a good chance you have a problem with gluten!
  3. Gut flora imbalance– Microbes in and on our bodies can either promote or detract from health.  One way this relates to thyroid function is based on the fact that 20% of the T4 released by the thyroid is converted into the active T3 hormone in the small intestine.  Lack of adequate amounts of hydrochloric acid in the stomach, and beneficial bacteria in the small intestine impairs the production of intestinal sulfatase  – a necessary ingredient to active thyroid hormone production.  In short, if the beneficial microbes are impaired in the intestine in any way, then this impairment alone can diminish circulating active T3 by as much as 20%.
  4. Microbial Toxins (low grade infection)-  This is related to number 3, but is listed separately due to the distinction by which it impairs thyroid function.  While number 3 relates to how a lack of beneficial bacteria may result in inadequate production of active T3 in the small intestine, number 4 relates to how harmful microbes within the gut may produce toxins which interfere with the conversion from T4 to active T3 in the liver.  Alterations in gut flora, and the waste products they create (lipopolysaccharides) may result in dominance of the liver converting T4 into rT3.  Too much rT3 relative to free T3 may be the most under diagnosed forms of thyroid dysfunction there is.
  5. Food Allergies–  While gluten sensitivity may certainly qualify as a food allergy, a distinction is made here for any food that creates an inflammatory response in the body.  There are certain immune system based chemicals that are produced upon exposure to certain foods that are particularly disruptive to thyroid function.  These inflammatory chemicals are called “cytokines”.  While many, if not most, food allergies are undoubtedly the result of “leaky gut”, some may be due to genetic factors.  The bottom line here is that if there are food allergies, there are cytokines, and if there are cytokines there is going to be functional thyroid impairment.  The impairment may again come from over producing rT3 relative to free T3, or it may occur elsewhere within the synthesis of thyroid hormone production.

Some researchers and clinicians who have been trying to assess how effectively the thyroid is functioning at the cellular level do not believe that blood tests are very accurate for diagnosing thyroid hormone problems.  Some of them believe body temperature is the most important value for assessing thyroid function.  Some research indicates that the most important value for assessing thyroid function is the very rarely performed test of measuring free T3 relative to rT3.  Again, the reason for this is that high amounts of rT3 may effectively block the activity of free T3 at the receptor site, a situation that is VERY common!  This is like somebody breaking a key off in a door lock, and you trying to get a different key in the lock.  It can’t happen, not until the rT3 is removed from the receptor site anyway.

Dr. Matthew Buckley
  • Dr. Matthew Buckley, PSc.D.