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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.

reverse T3 does not block T4 to T3 converson; but occupies T3 receptors and inhibits T3 stimulating receptors

low free T3: elevated reverse T3 in critically ill patients

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

reverse T3 and the free T3:rT3 can be used to assess prognosis of those with CHF.

effects of systemic illness on thyroid function: elevated Reverse T3 and low free T3

weight loss in obese children with low TSH and free T3 indicates high risk or regain of weight.  The important value here is the free T3.

Here is a great review of thyroid hormone metabolism published in the very relevant journal Endocrinology.  The review describes the peripheral metabolism of the pro hormone T4 and the peripheral metabolism to free T3 and/or reverse T3 and the associated metabolic implications.  Why don't more endocrinologists read?This is an animal study.

inflammation and critical illness associated with low TSH, low T3, elevated rT3 and low T3:rT3 ratio.

poor nutrition leads to low free T3 in tissue which lowers cellular metabolism which leads to obesity

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.

Here is an interesting finding:  low free T3 is significantly associated with increased cardiovascular and all-cause mortality in 7 prospective study on hospitalized patients.

reverse T3 comes from peripheral conversion from free T4

free T3 levels found to be higher in breast cyst fluid than in serum. This correlated with elevated K+/Na+ ratio which is associated with malignant transformation.  This elevated free breast cyst fluid correlated with estradiol concentration

free T3 is critical in the heart healing post MI.  Hypothyroidism and CHF share many hemodynamic and cardiovascular similarities.

T4 therapy (synthroid) alone does not increase serum free T3 concentrations in many patients

Study found no significant effect of subclinical hypothyroidism on weight in the elderly.  However, higher free T4 levels were associated with lower baseline weight and weight loss in women. TSH and free T3 were not. associated.

This article finds the mean TSH level in the "healthy" population to be 1.5.  Calls into question any level above that with symptoms of hypothyroid.  Full, adequate thyroid including free T3 and rT3 must be done.

Conclusions: Low basal fT3 concentration can reliably predict the occurrence of postoperative Atrial Fibrillation in Coronary-bypass patients