A 50-year-old woman complains of pain and swelling in her proximal interphalangeal joints, both wrists, and both knees. She complains of morning stiffness. She had a hysterectomy 10 years ago. Physical examination shows swelling and synovial thickening of the proximal interphalangeal (PIP) joints. Hemoglobin is 10.3 g/dL, MCV is 80 fL, serum iron is 28 mg/dL, iron-binding capacity is 200 mg/dL (normal 250-370 mg/dL), and saturation is 14%. Which of the following is the most likely explanation for this woman's anemia?