Gender-specific regulation of response to thyroid hormone in aging

We analyzed the results of 3564 thyroid function tests obtained from patients who received medication at both out- and inpatient clinics of Shinshu University Hospital. Subjects were from among those with thyroid function test results in the normal or mildly abnormal range. Based on a log-linear relationship between the concentrations of FHs and TSH, we established the putative resistance index to assess the relation between serum FH and TSH levels.Free thyroid hormone and TSH concentration showed an inverse log-linear relation. In males, there was a negative relationship between the free T3 resistance index and age. In females, although there were no relationships between age and FHs, the indices were positively related to age.These findings indicated that there is a gender-specific response to thyroid hormone with aging. Although the TSH level is a useful marker for the assessment of peripheral thyroid hormone action, the values should be interpreted carefully, especially with regard to age- and gender-related differences.In common with other systems, the endocrine system is affected by aging. With regard to thyroid hormone, age modifies the pituitary set point or response to comparably reduced free T4 (FT4) concentrations, resulting in lesser serum TSH elevation in older individuals [1]. TSH is suppressed in elderly subjects [2]. The decreased thyroid hormone levels observed in aging are due to lower TSH concentrations [3]. Centenarians exhibit significantly lower TSH levels together with slightly higher reverse T3 levels than aged controls [4]. In contrast to several reports on the association between low TSH level and senescence, heritable longevity has been reported to be associated with high serum TSH and low free T4 levels [5]. Exceptional longevity is associated with raised serum TSH [6,7]. Thus, the relation between the level of TSH and lifespan is controversial.TSH concentration is higher in women than in men [8]. TSH daily profiling demonstrated that TSH