 1. Subjects will be healthy male and female adult volunteers, between the ages of 18 and 65, able to provide informed consent. Patients younger than 18 are excluded as this is a purely physiologic study and we are unable to justify any potential risk. However, should our preliminary findings show potential clinically relevant benefits for children, the protocol could be modified to include them. Patients older than 65 are excluded due to intrinsic differences in thyroid hormone dynamics, compared with younger subjects, which could confound study interpretation. 