The observation that thyroid replacement therapy increases mortality in elderly subjects with subclinical hypothyroidism [1] has, as its converse, the documentation of an association between hypothyroidism and increased longevity in the animal model of hypothyroidism [2]. The corollary, in human subjects, is that a serum thyroid stimulating hormone (TSH) level which is at the upper level of the normal range also appears to be one which is associated with increased longevity [3]. In the latter study serum TSH levels were shown to be significantly (p<0.001) higher in subjects of median age 98 than in younger controls of median age 72 [3].
