Abstract: Increases in the blood levels of the hormone thyrotropin (TSH), which regulates thyroid function, can signal thyroid disease in older adults; but changes may also represent adaptations to aging or changes in pituitary function. It is important for medical practice to know the difference in order to use hormone therapy in those who need it while avoiding harm from over-treatment in those who don’t. The two groups look the same when TSH is measured, but we know that there are underlying processes that are very different. By analyzing simultaneous trends in multiple hormones (TSH and thyroid hormones) for 640 participants in the Baltimore Longitudinal Study of Aging with between 3-12 years of follow up, we have demonstrated that both age related changes and thyroid disease occur in people with similar TSH levels. Therefore, a single TSH level, the current means of diagnosing early thyroid failure, is not enough to plan treatment in older adults. We are looking for other tests that could be done to tell the difference between adaptation and disease. We will compare the activity of the TSH hormone, the ability of the pituitary to respond to stimulation, the presence of antibodies, and other blood tests that may serve as markers between these different groups of people. This work is important because when older adults are treated with thyroid hormone un-necessarily, it can do more harm than good by increasing the risk of irregular heart rhythms or bone loss. We know that doctors in the US and the UK have become more aggressive in prescribing thyroid hormone over the past decade, and the number of older adults is growing rapidly, lending increased urgency to this research.