- The most frequent underlying cause of iron deficiency anemia in adults is chronic blood loss, commonly from the gastrointestinal tract.
- This continuous loss depletes iron stores over time, leading to anemia.
- In adults, dietary iron deficiency is less common due to generally adequate intake, while malabsorption and increased requirements (e.g., pregnancy) are less frequent causes.
- Identifying and treating the source of blood loss is essential for management.

Reference: Davidson’s Principles and Practice of Medicine, 23rd Edition, Chapter: Disorders of Iron Metabolism and Anemia, Page 591.