Vitamin B-12 is a busybody nutrient involved in a wide range of physiological processes. Your B-12 needs have to come from either food or supplements, but the main problem with B-12 is that it’s poorly absorbed in your intestines, even under ideal circumstances. Some health issues further reduce B-12 absorption, which leads to serious problems.
Vitamin B-12 is needed by your body for producing energy, copying DNA, transmitting nerve signals, making red blood cells, supporting short-term memory and regulating mood and overall cognition. No other vitamin is as widely used in your body, but ironically, it’s the most difficult to absorb from food or supplements. For example, healthy people tend to absorb only about 1 percent or less of the B-12 they consume. Some B-12 is produced by bacteria in your large intestine, but it’s not able to be absorbed and used. B-12 is stored for many months or years in your liver, which is why deficiency symptoms tend to take a while to show up. Good sources of B-12 include meats, fish, seafood, dairy products, eggs and some fortified cereals.
Current recommendations for B-12 are between 2 and 3 micrograms per day, although there’s concern among some nutritionists, doctors and scientists that those levels are not enough, especially for older people. However, even if you aimed for just 3 micrograms daily, you may have to consume over 300 micrograms of B-12 to get enough because of its low absorption rate. Furthermore, to be able to absorb any B-12 through your small intestine, you need to produce enough intrinsic factor in your stomach. Intrinsic factor is a protein carrier that latches on to B-12 in your stomach and escorts it to your small intestine, where it can be absorbed.
Lack of Absorption
The main cause of complete malabsorption of B-12 is no intrinsic factor production or release from specialized cells in your stomach. Why this occurs is a bit of a mystery, although it’s assumed to be an autoimmune issue -- meaning the immune system produces antibodies that target and destroy these specialized cells. Stomach infection and ulceration also reduce the output of intrinsic factor. Inflammation of the small intestine -- perhaps due to gluten sensitivity or celiac disease -- also inhibits B-12 absorption. With no intrinsic factor and no B-12 absorption, a disease called pernicious anemia develops, which is characterized by deformed red blood cells that are too large and can’t carry oxygen properly. Pernicious anemia directly leads to extreme fatigue, weakness and pale skin. Other related symptoms of B-12 deficiency include sluggish metabolism, constipation and numbness in the limbs, as well as many issues related to brain function such as poor short-term memory, confusion, mood swings and depression
If your stomach doesn’t produce any intrinsic factor, then you have to consider other ways of getting B-12 into your body. Getting a monthly B-12 shot in your arm is the most effective, although taking dissolvable B-12 tablets under your tongue -- called sublingual -- may help prevent deficiency symptoms also. Your doctor can easily measure B-12 levels from a blood sample. Normal serum B-12 ranges from between 200 and 600 picograms per milliliter.
- PDR for Nutritional Supplements; Sheldon Hendler and David Rorvik
- Public Health Nutrition: From Principles to Practice; Mark Lawrence and Tony Worsley
- Textbook of Functional Medicine; David S. Jones
Sirah Dubois is currently a PhD student in food science after having completed her master's degree in nutrition at the University of Alberta. She has worked in private practice as a dietitian in Edmonton, Canada and her nutrition-related articles have appeared in The Edmonton Journal newspaper.