Thyroid Hormone Concentrations

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_Article: Thyroid Hormone Concentrations _

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The Journal of Clinical Endocrinology & Metabolism 2005; 90(12):6403–6409

Thyroid Hormone Concentrations, Disease, Physical Function and Mortality

in Elderly Men

Annewieke W. van den Beld, Theo J. Visser, Richard A. Feelders, Diederick

E. Grobbee, and Steven W. J. Lamberts

Department of Internal Medicine (A.W.v.d.B., T.J.V., R.A.F., S.W.J.L.),

Erasmus Medical Center, 3000 CA Rotterdam, The Netherlands; and Julius Center

for Patient Oriented Research (D.E.G.), University Medical Center Utrecht,

3508 GA Utrecht, The Netherlands

This study of 403 men investigated the association between TSH, T4, free

T4, T3, TBG and reverse T3 (rT3) and parameters of physical functioning.

This study demonstrates that TSH and/or T4 levels are poor indicators of

tissue thyroid levels and thus, in a large percentage of patients, cannot be

used to determine whether a person is euthyroid (normal thyroid) at the tissue

level. In fact, T4 levels had a negative correlation with tissue thyroid

levels (higher T4 levels were associated with decreased peripheral

conversion of T4, low T3 levels and high rT3). This study demonstrated that rT3

is

the best indicator of tissue levels of thyroid and was inversely correlated

with physical performance scores. The study also demonstrates that the

T3/rT3 ratio is currently the best indicator of tissue levels of thyroid.

This study showed that increased T4 and rT3 levels and decreased T3 levels

are associated with hypothyroidism at the tissue level with diminished

functioning and a catabolic state. This study adds to the mounting evidence

that giving T4 preparations such as Synthroid and Levoxyl are inadequate at

restoring tissue euthyroidism, and that a normal TSH cannot be relied upon

as an indication of euthyroidism, as it has a very low sensitivity and

specificity for hypothyroidism. This poor sensitivity and specificity is further

decreased with the presence of one or more systemic illnesses, including

diabetes, heart disease, hypertension, systemic inflammation, asthma, CFS,

fibromyalgia, rheumatoid arthritis, lupus, insulin resistance, obesity,

chronic stress and almost any other systemic illness.

Low T3 syndrome, with low T3 and high reverse T3, is almost always missed

when using standard thyroid function tests, as the T3 level is often in the

low normal range and reverse T3 is in the high normal range, again making

the T3/rT3 ratio the most useful marker for tissue hypothyroidism and as a

marker of diminished cellular functioning. The authors of this study state,

“Subjects with low T3 and high reverse T3 had the lowest PPS [PPS is a

scoring system that takes into account normal activities of daily living and

is a measure of physical and mental functioning]…Furthermore, subjects with

high reverse T3 concentrations had worse physical performance scores and

lower grip strength. These high rT3 levels were accompanied by high FT4

levels (within the normal range)…These changes in thyroid hormone

concentrations

may be explained by a decrease in peripheral thyroid hormone metabolism…

Increasing rT3 levels could then represent a catabolic state, eventually

proceeding an overt low T3 syndrome.â€

This study demonstrates that TSH and T4 levels are poor measures of tissue

thyroid levels, TSH and T4 levels should not be relied upon to determine

the tissue thyroid levels and that the best estimate of the tissue thyroid

effect is rT3 and the T3/rT3 ratio.