Vince
Super Moderator
CONCLUSION
The most important determinant of thyroid activity is the intra-cellular level of T3, and a major determinant of the intracellular T3 level is the activity of the cellular thyroid transporters. Reduced thyroid transport into the cell is seen with a wide range of common conditions, including insulin resistance, diabetes, depression, bipolar disorder, hyperlipidemia (high cholesterol and triglycerides), chronic fatigue syndrome, fibromyalgia, neurodegenerative diseases (Alzheimer's, Parkinson's and multiple sclerosis), migraines, stress, anxiety, chronic dieting and aging. The high incidence of reduced cellular thyroid transport seen with these conditions makes standard thyroid tests a poor indicator of cellular thyroid levels in these patient populations.The pituitary has different transporters than every other tissue in the body; the thyroid transporters in the body are very energy dependent and are affected by numerous conditions while the pituitary is minimally affected. Because the pituitary remains largely unaffected, there is no elevation in TSH despite wide-spread tissue hypothyroidism. This explains why TSH is an inaccurate marker for tissue T3 levels for a variety of patients.Reduced thyroid transport results in an artificial elevation in serum thyroid levels (especially T4), making this a poor marker for tissue thyroid levels, as well. Rather, an elevated or high-normal rT3 along with symptoms is shown to be a reliable marker for reduced transport of thyroid hormones and an indication that a person has low cellular thyroid levels despite having normal TSH, free T4, and free T3 levels (see Figure 2).The intracellular T3 deficiency seen with these conditions often results in a vicious cycle of worsening symptoms that usually goes untreated because standard thyroid tests look normal. Additionally, it is not surprising that T4 preparations are generally ineffective in the presence of such conditions, while T3 replacement is shown to be beneficial, with potentially dramatic results. In the presence of such conditions, it should be understood that significant intracellular hypothyroidism may remain undiagnosed by standard blood tests. On the basis of the data presented here, the free T3/rT3 ratio and a low SHBG, along with signs and symptoms, including basal body temperature and the reflex relaxation phase, appear to be a more appropriate method for assessing the presence of hypothyroidism and determining whether supplementation with T3 (rather than T4 only) should be considered in a particular patient.Thus, if a patient with a normal TSH presents with symptoms consistent with hypothyroidism, including fatigue, weight gain, depression, cold extremities, muscle aches, headaches, decreased libido, weakness, cold intolerance, water retention or PMS, a combination of both clinical and laboratory assessment should be used to determine the likely overall thyroid status and if a therapeutic trial of straight T3 or a T4/T3 combination is indicated.
https://restorativemedicine.org/journal/thyroid-hormone-transport-into-cellular-tissue/
