From the Guidelines
Iron, folate, and vitamin B12 are primarily reabsorbed in different parts of the intestine.
Reabsorption Locations
- Iron is mainly absorbed in the duodenum and proximal jejunum 1.
- Folate is absorbed in the duodenum and jejunum through a pH-dependent carrier-mediated process 1.
- Vitamin B12 is selectively absorbed in the terminal ileum, bound with gastric-derived intrinsic factor 1.
Key Factors
- The absorption of these nutrients is crucial for various bodily functions, including DNA synthesis, amino acid metabolism, and the formation of red blood cells.
- Factors such as pH, gastric acid, and specific transport proteins play important roles in the absorption of these nutrients.
- Conditions like inflammatory bowel disease can affect the absorption of vitamin B12, particularly if the distal ileum is affected 1.
From the FDA Drug Label
Vitamin B12 is bound to intrinsic factor during transit through the stomach; separation occurs in the terminal ileum in the presence of calcium, and vitamin B12 enters the mucosal cell for absorption The terminal ileum is the part of the intestine where vitamin B12 is reabsorbed.
- Iron and folate reabsorption locations are not directly mentioned in the provided drug label. 2
From the Research
Intestinal Absorption of Iron, Folate, and Vitamin B12
- Iron absorption primarily occurs in the duodenum and upper jejunum, but the provided studies do not specifically discuss iron absorption.
- Folate absorption can occur throughout the small bowel 3, 4.
- Vitamin B12 absorption is more specific, requiring a luminal binding protein and occurring mainly in the distal half of the small bowel, specifically in the distal ileum 3, 5, 6.
Mechanisms of Absorption
- Folate absorption involves intestinal brush border proteins and can occur through multiple systems 3.
- Vitamin B12 absorption involves intrinsic factor, haptocorrin, and transcobalamin, as well as their respective membrane receptors, with cubilin and amnionless being key components in the distal ileum 5, 6.
- The large intestine is also capable of absorbing water-soluble vitamins, including those synthesized by the normal microflora 7.
Clinical Implications
- Impaired absorption of folate and vitamin B12 can lead to deficiency and various health issues, including hematological and neurological disorders 3, 5, 6, 4.
- Certain conditions, such as celiac disease, liver disease, and gastrointestinal tract diseases, can compromise folate function and lead to deficiency 4.
- Inherited disorders, such as Imerslund-Gräsbeck syndrome and intrinsic factor deficiency, can also affect vitamin B12 absorption 5, 6.