What Prevents Vitamin B-12 Absorption?

Vitamin B-12 Absorption

Vitamin B-12 is bound to protein in foods of animal origin and must be split from the protein before it can be absorbed. Hydrochloric acid is one of the digestive juices in your stomach. It breaks the B-12 away from proteins, but another step is necessary for absorption. Cells in the lining of your stomach make a substance called intrinsic factor, which attaches to the free vitamin B-12. The combination of intrinsic factor and vitamin B-12 is absorbed through the lining of your small intestine.

Age and Lack of Stomach Acid

Adults need approximately 2.4 micrograms vitamin B-12 per day. According to the U.S. Office of Dietary Supplements, about 10 to 30 percent of older adults develop atrophic gastritis, a condition where the stomach loses the ability to make enough digestive juices, including hydrochloric acid. The lack of hydrochloric acid means that vitamin B-12 is not split from the proteins, so it can't be absorbed. Although older adults may not be able to absorb enough vitamin B-12 from foods due to this condition, they can still absorb sufficient amounts of vitamin B-12 from supplements. The U.S. Institute of Medicine urges adults over the age of 50 years to take B-12 supplements. The Centers for Disease Control and Prevention explains that B-12 supplements contain anywhere from 6 micrograms to 2,000 micrograms. Vitamin B-12 is safe at very high dosages. It is so safe that the Institute of Medicine hasn't found it necessary to set a tolerable upper limit for supplement intake. Your doctor can help you find the right dosage of vitamin B-12.

Pernicious Anemia

Pernicious anemia is an autoimmune disease, which means your immune system attacks normal body cells instead of foreign cells like viruses or bacteria. In the case of pernicious anemia, your immune system attacks the cells that make intrinsic factor. Without intrinsic factor, you can't absorb vitamin B-12. Pernicious anemia occurs in 1 to 2 percent of older adults, according to the Office of Dietary Supplements, and can result in vitamin B-12 deficiency anemia, which causes fatigue and neurological symptoms. Pernicious anemia requires medical attention because supplements taken in normal dosages cannot be absorbed and you may require muscular injections, so speak to your doctor if you are concerned about absorbing vitamin B-12.

Intestinal Disorders and Surgery

People who have inflammatory digestive tract diseases such as Crohn's disease or celiac disease may not be able to absorb vitamin B-12. Crohn's disease causes inflammation of the lining of your digestive tract, which can lead to abdominal pain, severe diarrhea and even malnutrition and loss of absorption of certain nutrients, including vitamin B-12. Celiac disease is another inflammatory disorder of the digestive tract. People with celiac disease cannot digest gluten -- a protein found in wheat, rye and barley. They suffer from symptoms such as weight loss and diarrhea and have problems absorbing certain nutrients. Surgical procedures that remove part of the stomach or small intestine might also reduce the body's ability to absorb vitamin B-12.