Mechanistic Study of Subclinical Hypothyroidism In the Elderly

Inclusion Criteria: 1. men and women aged 70 and older 2. TSH between 4.5 and 19.9 mU/L as an outpatient 3. ability to provide informed consent Exclusion Criteria: Laboratory Tests: 1. TSH \<4.5 mU/L or \>20 mU/L on repeat testing at least four weeks later or free T4 level outside the reference range 2. thyroid peroxidase (TPO) antibody positive 3. abnormal liver function tests (LFTs \>3 x upper limit of normal) 4. hemoglobin \<11 g/dL Surgeries or Procedures: 1. thyroid surgery 2. pituitary surgery 3. bariatric surgery 4. bowel resection involving the jejunum and upper ileum 5. radioactive iodine therapy 6. radiation treatments to head or neck Medical Conditions: 1. diagnosis of pituitary disease 2. diagnosis of amyloidosis, sarcoidosis, hemochromatosis 3. diagnosis of adrenal insufficiency 4. obesity with BMI \> 35 mg/kg2 5. history of stroke 6. chronic or ongoing angina, Class II or higher congestive heart failure, or uncontrolled hypertension with current blood pressure greater than 160/100 7. diabetes mellitus with hemoglobin A1C level greater than 8.0% in the past six months 8. celiac sprue, Crohn's disease, ulcerative colitis, Zollinger-Ellison syndrome 9. renal insufficiency with calculated glomerular filtration rate \<45 cc/min 10. cognitive impairment with Mini Mental State Exam\[30\] \<24/30 11. history of any seizures 12. unstable medical or psychological condition in the judgment of the principal investigator Medications: 1. thyroid hormone preparations 2. antithyroid drugs 3. medications that interfere with the absorption or metabolism of thyroid hormone 4. medications that interfere with the TRH stimulation test 5. proton pump inhibitors