Despite the fact that most people in the United States consume the recommended daily intake of vitamin B-12, 1.5 to 15 percent of the population suffers from a vitamin B-12 deficiency, according to the National Institutes of Health Office of Dietary Supplements. Vitamin B-12, one of the eight essential B vitamins, helps keep the cardiovascular system healthy by helping convert the amino acid homocysteine, a substance believed to contribute to heart disease, into methionine. The human body also needs vitamin B-12 to produce red blood cells, support neurological function and create genetic material for new cells. Because many factors affect the absorption of vitamin B-12, a decreased level may occur even when you meet the recommended daily intake.
Inadequate Intake
The National Institute of Medicine Food and Nutrition Board recommends that adults consume 2.4 micrograms (mcg) of vitamin B-12 per day. This amount seems small, but foods naturally contain small amounts. Only animal food sources contain vitamin B-12; for example, 1 cup of milk contains 0.9 mcg of vitamin B-12. Failing to consistently consume this amount daily can lead to decreased vitamin B-12 levels. Vegetarians, and particularly vegans who consume no animal products, have a high risk for vitamin B-12 deficiency. Doctors suggest vegetarians, especially pregnant females and lactating mothers, take vitamin B-12 supplements to avoid a deficiency.
Low Stomach Acid
In food sources, vitamin B-12 binds to the protein. In order for your body to absorb vitamin B-12, it must first separate the vitamin B-12 from the protein. This separation step occurs in the stomach when the hydrochloric acid breaks the bonds between the protein and the vitamin. A medical condition known as atrophic gastritis affects 10 to 30 percent of those individuals over the age of 60, according to the Linus Pauling Institute, causing inflammation of the stomach that can lead to a peptic ulcer. Treating a peptic ulcer requires taking medication to reduce stomach acid production, which can lead to a vitamin B-12 deficiency.
Absorption Inhibition
If you suffer from a stomach or intestinal disorder, your level of vitamin B-12 may be decreased. Crohn's disease causes inflammation of the lining of the digestive tract that can inhibit the absorption of nutrients, including vitamins. Celiac disease, a condition caused by the immune system mistakenly attacking the lining of the small intestine in response to the protein in wheat, rye and barley, also causes inflammation that interferes with vitamin absorption. Those individuals with these disorders may experience symptoms of vitamin B-12 deficiency including a reduction in cognitive function that ranges from mild to dementia, numbness and tingling in the arms and legs, disorientation and anemia.
Decreased Pancreatic Enzymes
After the stomach acid separates the vitamin B-12 from the protein, the free vitamin binds to specialized proteins as it travels to the small intestine. Once in the small intestine, enzymes produced by the pancreas degrade these proteins, leaving the vitamin B-12 free to bind with intrinsic factor -- another specialized protein produced by the parietal cells in the stomach. The intrinsic factor-vitamin B-12 complex then gets absorbed through the small intestine into the bloodstream. Conditions that affect the ability of the pancreas to produce pancreatic enzymes, such as acute or chronic pancreatitis, can inhibit the absorption of vitamin B-12 and lead to a deficiency.
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