Normal age-related changes in thyroid hormone economy.

Aging is associated with significant changes in the anatomy of the thyroid gland and in the physiology of hypothalamic-pituitary-hormone thyroid axis. In addition, tissue responsiveness to thyroid hormone may also be altered with age. However, age alone should not influence the interpretation of commonly obtained thyroid function tests. The reduced thyroid hormone clearance with age explains the reduced daily replacement doses of thryoxine in hypothyroid elderly subjects.