Summary statements

• THs impact metabolic, cardiovascular, cognitive, and musculoskeletal parameters.

• Serum TH levels are only a surrogate marker and may not reflect what is taking place at the cellular level.

• Physiologically measurable parameters (such as heart rate, body weight, and REE) are the ultimate reflection of TH action in cells and allow for assessment of a euthyroid state.

• Assessments of metabolic, cardiovascular, cognitive, and musculoskeletal parameters should be included in clinical trials of combination therapy.