[Variations in the anatomy and physiology of the thyroid gland in old age]

Recently, the anatomical and physiological modifications of thyroid gland in the elderly have been undergone to many investigations. However, it does not exist an univocal interpretation about the results. Furthermore, non-thyroidal diseases, in the elderly, can modify TSH, FT3 and FT4 serum levels because of an important inhibition of T3 and T4 peripheric conversion; moreover, many drugs have been reported interactions with hypothalamus-hypophysis-thyroid axis in the senescence. At present, the international literature confirm, in the elderly, a reduction of the activity of the hypothalamus-hypophysis-thyroid axis, associated with an adaptation of hormones production; moreover, the thyroid gland undergoes anatomical (weight) and physiological (captation of iodine and hormones synthesis) adaptations, age-related, which witness for a reduction of thyroid function. Furthermore, FT3 and FT4 plasma levels present in old persons are comparable to younger subjects; in fact, in the elderly, it has been proved a reduction of T4 peripheric degradation which equilibrates its low production. So, the progressive reduction of thyroid gland activity in the old men must be explained like an adaptation to the new metabolic rhythm associated with a reduced TSH secretion and with a smaller body mass in the elderly. However, this peculiar new steady-state is not like an hypothyroidism syndrome, because there is not a real hormones reduction.