Several factors impact vitamin B-12 absorption, including digestive health, the source of B-12 and the dosage. While no one formula predicts vitamin B-12 absorption, research suggests that the higher the dosage, the smaller the percentage of B-12 absorbed. Deceased absorption at higher dosages is due to the limited capacity of intrinsic factor, a protein your stomach produces that binds to vitamin B-12, according to the Office of Dietary Supplements.
General Guidelines
A healthy individual absorbs roughly 56 percent of a 1 mcg dose of vitamin B-12. Intrinsic factor maxes out at 1 to 2 mcg, beyond which the percentage of B-12 the body can absorb is notably reduced. Individuals with pernicious anemia, a condition marked by inadequate red blood cell production, suffer from vitamin B-12 deficiency because the stomach isn't able to produce intrinsic factor. When this condition is present, your body can only absorb vitamin B-12 through passive diffusion, meaning that you consume a dosage high enough to absorb an adequate amount without the benefit of intrinsic factor. Another option is to bypass the process of absorption by injecting B-12 directly into muscle.
Specific Absorption Concerns
Surgical procedures -- such as weight-loss surgery -- that remove a portion of the stomach may negatively affect the stomach's production of intrinsic factor, affecting the capacity for vitamin B-12 absorption. In such cases, make sure your doctor monitors your B-12 levels for signs of deficiency. For individuals who are not able to produce intrinsic factor, it takes high doses of vitamin B-12 to ensure absorption of small amounts. Of a 1,000 mcg dosage, roughly 1 percent, or 10 mcg, is absorbed when intrinsic factor is lacking, according to the Linus Pauling Institute.
Recommended Dosage
If you follow a vegan diet or limit sources of vitamin B-12 such as meat, poultry and fish, you may benefit from a daily B-12 supplement of 1 to 25 mcg. For vitamin B-12 deficiency, a higher dosage of 647 to 1,032 mcg may be effective, according to MedlinePlus. Check with your doctor about the form and dosage of vitamin B-12 supplements.
Considerations
Foods fortified with vitamin B-12 contain the same crystallized form of this nutrient that supplements provide. Ideal for individuals with low concentrations of stomach acid, the crystallized form of vitamin B-12 doesn't depend on stomach acid to separate it from food protein, making it more readily available for absorption. Besides fortified cereal, plant-based sources of B-12 include nutritional yeast, fortified soymilk and fortified meat substitutes.
References
- Office of Dietary Supplements: Dietary Supplement Fact Sheet: Vitamin B-12
- Linus Pauling Institute at Oregon State University: Vitamin B-12
- MedlinePlus: Vitamin B-12
- Vegetarian Resource Group; Vitamin B-12 in the Vegan Diet; Reed Mangels, Ph.D., R.D.
- National Heart, Lung and Blood Institute: What Is Pernicious Anemia
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