Iron deficiency is the most common nutritional deficiency worldwide and is a leading cause of anemia, which can result in symptoms such as fatigue, weakness, shortness of breath, and reduced quality of life. This study aims to better understand why some people develop iron deficiency by examining how the body absorbs iron and how this may relate to diet and proteins involved in iron absorption. Participants will complete questionnaires, provide blood, urine, and stool samples, undergo an oral iron absorption test, and complete a short food diary. If an upper endoscopy is already being performed as part of routine medical care, one additional biopsy sample will be collected during the procedure for research purposes. The information gathered may help improve the diagnosis and evaluation of iron deficiency anemia in the future. Participation involves two study visits over approximately one month. There is no direct medical benefit to participants, but the knowledge gained may benefit future patients with iron deficiency anemia.

We wish to examine human liver to determine whether and to what extent paxillin is expressed (using immunohistochemistry). Existing liver specimens will be identified by ICD-10 search to identify patients with MASLD who have undergone liver biopsy within the last 5 years.