Vitamin B-12 is predominantly found in animal protein, although some plant food products include the nutrient. Pegged as the most complexly structured vitamin, B-12 is vital to healthy red blood cell development, metabolism, nervous system maintenance and DNA synthesis. While most people who consume well-balanced diets get enough vitamin B-12, certain conditions impair its absorption. If your vitamin B-12 intake or absorption is below a healthy level, your doctor may prescribe supplements, recommend dietary changes or a combination of both.
Nutrient Facts
Vitamin B-12 deficiencies are more common in adults over age 60, but may also occur in individuals with anemia or gastrointestinal disorders, as well as those who follow vegan diets. In healthy people, a protein called intrinsic factor -- which binds to vitamin B-12 and makes it available to perform its natural functions -- is produced in the stomach. Before intrinsic factor can attach to B-12, the nutrient is separated from food sources by acids and enzymes in the stomach. If normal amounts of acids and intrinsic factor are present, food sources of vitamin B-12 are generally enough to meet demand. If not, or if your diet is low in sources of vitamin B-12, supplementation may be necessary.
Supplementing Your Diet
If your primary need for vitamin B-12 supplements stems from your dietary choices, a small oral dose of up to 25 mcg daily is typically enough. Your body can only absorb a certain amount of vitamin B-12 at a time due to the limited capacity of intrinsic factor. Over-the-counter supplements are available in oral tablets, chewable varieties and sublingual preparations in tablet, lozenge or liquid form. The bioavailability of these supplements is comparable.
Bypassing Absorption Problems
If you have difficulty absorbing vitamin B-12 due to low levels of stomach acid or intrinsic factor, your doctor may recommend administering the nutrient via injection or nasal gel. This method of supplementation bypasses the ordinary process of separating B-12 from food protein, and is used to treat severe deficiencies, pernicious anemia and other conditions that limit absorption. As an alternative to injections, high oral doses of B-12 may be prescribed. At high dosages, a small amount of B-12 may be absorbed through passive diffusion.
Considerations
Adults need roughly 2.4 mcg of vitamin B-12 daily, although 2.6 and 2.8 mcg daily are recommended for pregnant and lactating women, respectively. One serving of steamed crab or clams, for example, provides more than enough B-12 to meet daily recommendations, if absorption is not an issue. A 3 oz. serving of baked salmon provides 2.4 mcg, while the same size portion of beef provides 2.1 mcg. Vegans can get vitamin B-12 from fortified foods such as breakfast cereal, plant milks including some brands of rice and almond milk, soy products and nutritional yeast. Consult with your doctor about your supplemental and dietary needs, as well as the proper administration and dosage of vitamin B-12.
References
- Linus Pauling Institute at Oregon State University: Vitamin B-12
- Office of Dietary Supplements: Dietary Supplement Fact Sheet: Vitamin B-12
- Medline Plus Encyclopedia: Vitamin B-12
- Medline Plus: Vitamin B-12
- Vegetarian Resource Group; Vitamin B-12 in the Vegan Diet; Reed Mangels, Ph.D., R.D.
- Vegan Health: What Every Vegan Should Know About Vitamin B-12
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