The AGNP has an 82-year-old patient with diabetes, heart dis…

The AGNP has an 82-year-old patient with diabetes, heart disease, depression and history of prostate cancer, has a normocytic anemia, Hgb of 9.6 (low). He has had a recent colonoscopy which was normal, and his stools are negative for blood. His diet history reveals a consistent cardiac diet, with lean protein (including some low-fat red meat), whole grains, and plenty of fruits and vegetables, (including dark leafy greens). He has had no weight loss or weight gain.  His is anemia is likely related to: