By Reed Mangels, PhD, RD
Myths about vitamin B12 abound. For example, there’s the myth that sources of vitamin B12 include everything from rainwater to potatoes. In truth, reliable sources of vitamin B12 for vegans are foods fortified with this vitamin (for example soymilk, breakfast cereals, meat substitutes, etc. — read the label) and supplements. That’s it. You can read more about vitamin B12 sources on The Vegetarian Resource Group website: http://www.vrg.org/nutrition/b12.php
Then there’s the whole question of absorption. Getting vitamin B12 into our bodies in a form so that it can be used is much more complicated than just drinking a glass of fortified soymilk. Of course, we’re not aware of all of the steps, but it is quite a process. It’s actually simplest for vitamin B12 that is not bound with protein. This would be the case for vegan sources of the vitamin. In contrast, sources from animals like meat, fish, dairy products, and eggs have even more steps to go through, since in these products, vitamin B12 has to be released from food protein before it can be absorbed.
Let’s say that you take a multi-vitamin that contains vitamin B12. In the stomach, and possibly to some extent in the mouth, the multi-vitamin is digested so that the binders that hold the different kinds of vitamins together dissolve. Vitamin B12 is now able to connect up with a special protein, called R protein, which our body makes and which is found in saliva and in the digestive juices in our stomach. The R factor-vitamin B12 complex leaves the stomach and moves into the first part of the small intestines. There, enzymes make the pancreas digest the R protein so that vitamin B12 is able to connect to intrinsic factor, a substance made by cells in our stomach. Vitamin B12 has to be connected to intrinsic factor to keep the vitamin from being destroyed by enzymes in the small intestine. Once the intrinsic factor-vitamin B12 complex gets to the ileum (the last part of the small intestine), it is absorbed into the blood, vitamin B12 is released from the intrinsic factor and connected to a protein that transports it in the blood (1-3). The same process would take place whether you’re getting vitamin B12 from a multi-vitamin, a fortified food, or a vitamin B12 supplement.
Sublingual vitamin B12 supplements are on the market. These can be taken in sublingual form (allowed to dissolve under the tongue). This can be a way to get vitamin B12 into the body without having to go through all the steps described above. However, sublingual vitamin B12 does not seem to be more effective than oral vitamin B12 (4).
References
1. Medeiros DM, Wildman REC. Advanced Human Nutrition, 3rd edition. Burlington, MA: Jones and Bartlett Learning, 2015.
2. National Institutes of Health Office of Dietary Supplements. Vitamin B12 Dietary Supplement Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/ 2016.
3. Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press, 1998.
4. Yazaki Y, Chow G, Mattie M. A single-center, double-blinded, randomized controlled study to evaluate the relative efficacy of sublingual and oral vitamin B-complex administration in reducing total serum homocysteine levels. J Altern Complement Med 2006;12:881-5.
If you’d like to read more about vitamin B12, try these websites:
Jack Norris, RD’s excellent webpage – Vitamin B12 – Are You Getting It?
NIH Office of Dietary Supplements. Vitamin B12 Fact Sheet for Consumers
Linus Pauling Institute Micronutrient Information Center. Vitamin B12