1. Chronic inflammatory diseases such as rheumatoid arthritis, lupus, and Crohn's disease.
2. Chronic infections such as HIV/AIDS, tuberculosis, and hepatitis C.
3. Cancer and its treatments, including chemotherapy and radiation.
4. Long-term use of certain medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs) and certain antibiotics.
5. Poor nutrition, including inadequate intake of iron, folate, and vitamin B12.
6. Blood loss, such as from heavy menstrual periods or gastrointestinal bleeding.
7. Kidney disease.
8. Genetic disorders, such as thalassemia and sickle cell anemia.