What should I know about ursachen fur vitamin b 12 mangel?

Vitamin B12 deficiency has multiple causes. The most common is inadequate dietary intake, especially in strict vegans or vegetarians, as B12 is almost exclusively found in animal products. Malabsorption is another major factor: chronic inflammatory bowel diseases (Crohn's, ulcerative colitis), atrophic gastritis (e.g., pernicious anemia), gastric or intestinal surgery, and long-term use of proton pump inhibitors (PPIs) or metformin. Aging reduces the ability to absorb food-bound B12 due to declining stomach acid. Genetic variants in FUT2 (affecting intestinal B12 uptake) or TCN2 (transport protein) can also influence B12 status. Deficiency often presents late with neurological symptoms, fatigue, or macrocytic anemia. Diagnosis should include holotranscobalamin (active B12) or methylmalonic acid (MMA), as serum B12 alone can be misleading. Caveat: a normal serum B12 does not rule out functional deficiency. Evidence is clinically well-established, though some genetic associations lack large-scale replication.