Mechanistic Study of Subclinical Hypothyroidism In the Elderly

Oral levothyroxine with a total starting dose of 0.7mcg/kg/day split into three daily doses will be titrated to a target TSH level of 0.5 -1.5mU/L

Oral liothyronine with a starting dose of 1/3 of the weight-based LT4 dose divided into three daily doses titrated to a target TSH level of 0.5 -1.5mU/L

200 µg intravenous TRH will be given at study visit 1 (baseline), study visit 2 (on first thyroid treatment), and study visit 3 (on second thyroid treatment).