Aging itself has only minor effects on the thyroid gland and thyroid hormones. As people get older, the thyroid gland shrinks and shifts lower in the neck. The level of the thyroid hormone triiodothyronine (T3) may fall slightly, but the speed of vital functions changes very little. However, thyroid disorders become more common with aging.

Disorders that affect thyroid function, particularly hyperthyroidism and hypothyroidism, can be thought of as great masqueraders in older adults. These disorders often cause symptoms that are easily mistaken for symptoms of other conditions or even as signs of getting old.

Increased or decreased thyroid function can dramatically worsen the way an older adult feels and can greatly diminish the ability to carry out daily activities. For these reasons, the great masqueraders must be unmasked and recognized for what they are so that they can be effectively treated.

Some experts recommend measuring the level of thyroid-stimulating hormone in the blood in people over 70 years old every year or every few years, although a number of medical bodies that have examined this question recommend against screening adults who have no symptoms in order to avoid over-treating people with minor laboratory abnormalities.