Foods high in Vitamin B-12

Vitamin B12 is essential for forming red blood cells and DNA and for maintaining the nervous system, and it has one defining trait that shapes who needs to pay attention to it: it occurs naturally only in animal foods. Vegans and vegetarians are the clearest dietary risk group, since plant foods contain no natural B12 unless fortified. But diet is only part of the picture — absorbing B12 also depends on stomach acid and a protein called intrinsic factor, so a surprisingly large share of adults over 50 absorb B12 less efficiently regardless of how much they eat. People taking metformin, or long-term acid-reducing medications like proton pump inhibitors or H2 blockers, along with anyone who has had gastric or intestinal surgery, celiac disease, Crohn's disease, or pernicious anemia, are also more likely to run low even on a diet that looks adequate on paper. Because the liver stores several years' worth of B12, deficiency from diet changes alone tends to develop slowly, while an absorption problem can cause it to show up much faster. The list below ranks foods and ingredients by measured vitamin B12 content per the amount tested. Organ meats, shellfish like oysters and clams, and other animal proteins dominate the higher end of the ranking, since these are the most concentrated natural sources; fortified foods are the only way plant-based eaters appear on a comparable list at all.

Adults need about 2.8000 UG/day (age 19+) — Harvard Nutrition Source (directly fetched).