Inclusion:

1. 60 healthy post-menopausal women (ages 55 to 80 y);
2. BMI 18-30 kg/m2
3. Community dwelling; and voluntarily consenting

Exclusion:

1. Recent use of psychotropic or neuroactive drugs (within five biological half-lives);
2. Obesity (outside weight range above);
3. Laboratory test results not deemed physician acceptable, cholesterol >250, triglycerides > 300, BUN >30 or creatinine > 1.5 mg/dL, liver function tests exceeding twice upper limit of normal, electrolyte abnormality, anemia;
4. Drug or alcohol abuse, psychosis, depression, mania or severe anxiety;
5. Systemic inflammatory disease;
6. Endocrinopathy, other than primary thyroidal failure receiving replacement;
7. Nightshift work or recent transmeridian travel (exceeding 3 time zones within 7 days of CRU admission);
8. Acute weight change (loss or gain of > 2 kg in 6 weeks);
9. Systemic illness
10. Unwillingness to provide written informed consent.
11. Allergy to anastrozole or fulvestrant (treatment drugs).
12. History or suspicion of breast cancer.
13. History of carcinoma (excluding localized basal cell carcinoma removed or surgically treated with no recurrence).
14. History of thrombotic arterial disease (stroke, TIA, MI, angina) or deep-vein thrombophlebitis.
15. History of CHF, cardiac arrhythmias, congenital QT prolongation, and medications used to treat cardiac arrhythmias.
16. Pre-menopausal status as determined by screening hormone measurements.