Positive association between circulating free thyroxine and insulin-like growth factor l concentrations in euthyroid elderly individuals.
OBJECTIVE
Previous studies have shown marked changes in circulating insulin-like growth factor-l (IGF-l) levels in hypo- and hyperthyroid patients. In this study we examined whether the circulating concentration of IGF-l may also be affected by normal thyroid hormone levels.


METHODS
A cross-sectional study of thyroid hormones and plasma IGF components in a population-based sample.


METHODS
50-80 year-old men (n = 262) and women (n = 218) with normal concentrations of serum free thyroxine (fT4), free triiodothyronine (fT3) and thyrotrophin (TSH).


METHODS
Plasma concentrations of IGF-l, IGF-ll and IGFBP-3, and serum concentrations of TSH, fT3 and fT4.


RESULTS
Serum fT4 values were weakly positively correlated and serum TSH levels were inversely correlated with circulating IGF-l concentrations. The associations persisted after adjustment for age and ideal body weight.


CONCLUSIONS
Our data demonstrate that thyroid hormones are positively correlated to IGF-l plasma levels even under physiological conditions. However, thyroid hormones explain only 1-2% of the normal variability of circulating IGF-1.
Seck
T
T
Department of Internal Medicine l, University of Heidelberg, Germany.
Scheidt-Nave
C
C
Ziegler
R
R
Pfeilschifter
J
J
D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D007335:Insulin-Like Growth Factor II / Q000032:analysis; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood
D018972:Insulin-Like Growth Factor Binding Protein 3; D014284:Triiodothyronine; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013972:Thyrotropin; D013974:Thyroxine