COMPLEX ALTERATION OF THYROID-FUNCTION IN HEALTHY CENTENARIANS

Several changes in thyroid function have been described in the elderly and largely attributed to concomitant nonthyroidal illness. The exten t to which aging per se contributes to these changes remains to be elu cidated, and scanty data are available in extremely old subjects. The present study was designed to focus on thyroid function during physiol ogical aging, taking advantage of two groups of selected aged individu als: group A of healthy centenarians (n = 41; age range, 100-110 yr) a nd group B including healthy elderly subjects selected by the criteria of the EURAGE SENIEUR protocol (n = 33; age range, 65-80 yr). Control groups included 98 healthy normal adult subjects (group C; age range, 20-64 yr) and 52 patients with miscellaneous nonthyroidal illness (gr oup D; age range, 28-82 yr). Our previous report of a low prevalence o f thyroid autoantibodies in centenarians was confirmed and extended by the finding of a similar low autoantibody prevalence in the highly se lected healthy elderly population of group B. Subclinical primary hypo thyroidism was found in 3 (7.3%) centenarians, and their data were exc luded from further statistical evaluation. No significant difference w as found in the median serum free T-4 levels of groups A-C. Median (an d range) serum free T-3 (FT3) was lower in centenarians [3.67 pmol/L ( 2.3-5.5)] than in group B [5.22 pmol/L (3.4-6.1)] and group C [5.38 pm ol/L (2.9-8.4); P < 0.0001 vs. both groups]. Similarly, the median ser um TSH level of centenarians [0.97 mU/L (<0.09 to 2.28)] was lower tha n those in groups B [1.17 mU/L (0.53-2.74)] and C [1.7 mU/L (0.4-4.8); P < 0.0001 vs. both groups]; moreover, serum TSH was also significant ly (P < 0.01) lower in group B than in group C. Both serum FT3 and TSH concentrations showed a significant inverse correlation (r = -0.634; P < 0.0001 and r = -0.377; P < 0.0001, respectively) with age. Median serum FT3 in centenarians was lower than that in group D patients [4.6 1 pmol/L (2.15-6.6); P < 0.0001]. In contrast, median serum rT(3) in c entenarians [0.40 nmol/L (0.20-0.77)], although higher than those in g roups B [0.24 nmol/L (0.15-0.37); P < 0.0001] and C[0.22 nmol/L (0.05- 0.46); P < 0.0001], was significantly lower than that in group D [0.60 nmol/L (0.13-2.08); P < 0.0001]. In conclusion, thyroid function appe ars to be well preserved until the eight decade of life if healthy sub jects are studied, whereas a reduction of serum FT3 is observed in ext reme aging. This phenomenon appears to be the consequence of both redu ced thyroid activity, resulting from decreased serum TSH concentration , and impairment of peripheral 5'-deiodinase.