Relationship of Age to the Thyroidal Accumulation, Renal Excretion and Distribution of Radioiodide in Euthyroid Man

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Abstract
Thyroidal accumulation, renal excretion and blood levels of radioiodide after intravenous administration have been measured in 131 middle-aged and elderly euthyroid, reasonably healthy men, 41 to 94 years of age. Thyroidal plasma radioiodide clearance and thyroidal radioiodide accumulation at 2 and 6 hours show statistically significant decreases with advancing age. Over the relatively narrow age span, 50–89 years, thyroidal radioiodide accumulation measured at 24 hours shows no change. A marked and statistically significant decrease with age in renal clearance of radioiodide is apparent. The radioiodide space does not change, but the plasma level at 6 hours increases with age. The latter finding is attributed to the decrease in renal clearance with age. Comparison of these results with those of others suggests that there exists an age-dependent decrease in thyroidal accumulation of radioiodide and in plasma radioiodide clearance. Within the interpretive limitations of the techniques, the changes reported are consistent with the view that thyroid hormone production decreases with advancing age.