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replacement therapy for hypothyroidism must include both T4 and T3

This article reviews the genetic polymorphisms that play role in low T4 to T3 conversion and thus combination T4/T3 therapy is indicated.  This study fails to recognize the environmental impacts on the deiodinase enzymes.

reference review suggests improved results with combined T4/T3 treatment for hypothyroid patients.  Also, a good review of thyroid metabolism.  Patients prefer the combination therapy versus T4 alone indicating improved symptoms with combined therapy.

combined T4/T3 therapy the best approach in hypothyroidism

Hashimoto's hypothyroidism is associated with a 44% increase in Heart disease in women under the age o 49.  A non-significant change was seen in men.  This study found that T4 therapy reduced this risk.  A better study would have been if T4 was compared to T4 + T3.

Anything and everything one would want to know regarding thyroid hormone signaling.  Doctors, especially endocrinologists, need to read this.  T4 is not or is ever inside target cells.  The enzymes, deiodinase types 1, 2, and 3, are what control the thyroid hormone at the cellular levels.  Deiodinase-2 is what generates T3 in the cytosol of the cell.  In contrast, deiodinase-3 is what generates rT3 which is inactive.  High Fat diet increases deiodinase-3.

what a silly study!  They look at free T4, the weakest thyroid hormone and found high levels to be associated with dementia.  However, they failed to assess free T3, the most biologically active, and reverse T3, inactive.  This study was like they intentionally blinded themselves of the body's physiology to study dementia.  This is the problem with a lot of research today: they have forgotten their foundation. Many older adults struggle with poor free T4 to free T3 conversion and high reverse T3 conversion.  So, without knowing what these clients were doing in these pathways makes their conclusion obsolete.

T3 shown increase weight loss, lower LDL, decrease apolipoprotein B, decrease T cholesterol versus T4.  This flies in the face of conventional medical dogma, that T 4 (synthroid, levothyroxine) is the only route of thyroid replacement.  In fact, this suppports the use of armour thyroid, a T4/T3 combination.

Study finds desiccated thyroid (armour thyroid) was associated with great weight loss, mood improvement than T4 alone.  Desiccated thyroid was preferred by patients in the study.  Conversion rate was 100 mcg T4 to 88 mg desiccated thyroid.

Armour Thyroid (T4 and T3 combined) provides better symptom control when compared to synthroid alone (T4)

Crossover study finds T3 versus T4 results in more weight loss, improved lipid management and increased SHBG without any adverse cardiovascular effects.   The T3 was dosed 3 x daily due to its short half life compared to T4.

Patients feel better taking both T4 and T3 compared to those taking just T4

rat model finds T4 and rT3 receptors at plasma membrane.  T3 was found to bind with lower affinity than rT3 and T4 at the same receptor binding site.

T4 upregulates PD-1 and tetrac, T4 analog, inhibits.

Metformin shown to suppress TSH secretion without change in free t4 or free t3 levels.  This again, shows the lack of reliability of the test TSH.  With the suppression of TSH indicated in this study, the free t4 and t3 should have been elevated, but were obviously not.

oxidative stress decreased type 1 deiodinase activity and thus T4 to T3 conversion, resulting in increased rT3 production.  Of interesting note, Alpha lipoic acid increased type I deiodinase activity and T4 to T3 conversion.

Wow!  JCEM states, "...it may be time to consider a personalized regime of thyroid hormone replacement therapy in hypothyroid patents."  Otherwise stated, combination T4, T3 provides a more customized thyroid replacement therapy than synthroid alone.

patients on synthroid only improved when switch to combined T4/T3 (armour thyroid)

thyroid replacement is not just about T4 (synthroid); but about T3, which is 5.4 x more potent

low free T3:elevated reverse T3 correlates with major depression and TSH and free T4 do not.