About 1.5 to 15 percent of Americans are deficient in vitamin B12 according to the National Institutes of Health. B12 deficiency leads to anemia, neurological disorders, and increases your cardiovascular disease risk. Vitamin B12 is required for red blood cell formation, nerve cell function, and DNA synthesis. It is a necessary cofactor in the conversion of homocysteine to methionine. High levels of homocysteine are associated with cardiovascular disease. B12 is also necessary for enzymatic processes of fat and protein metabolism. Symptoms of B12 deficiency can show up as loss of energy, tingling, numbness, reduced sensitivity to pain or pressure, blurred vision, abnormal gait, sore tongue, poor memory, and personality change.. Vitamin B12 exists in several forms and is present in some foods such as beef liver, beef, fortified cereal, eggs, milk products, and nutritional yeasts. It is also available as a supplement, prescription medicine, and as an injection. Although the majority of Americans take in sufficient amounts of B12, there are some groups of people that are deficient or at risk of becoming B12 deficient.
People with gastrointestinal disorders
People with celiac, Crohn’s disease, gastrointestinal tract surgery, and other stomach or small intestinal disorders are at risk for B12 deficiency, because they may be unable to absorb sufficient amounts of vitamin B12 from food. These orders are often associated with loss of cells that produce hydrochloric acid and intrinsic factor, which are required for the extraction and absorption of vitamin B12. Protein pump inhibitors, which are used to treat reflux disease and peptic ulcer, may also interfere with B12 absorption by slowing the release of gastric acid by the stomach. The symptoms of B12 deficiency may start with mild cognitive decline and slowly over a periods of years progress to anemia, nerve damage, and dementia.
People over 50
According to the National Institutes of Health about 10 to 30 percent of older people develop atrophic gastritis, where the cells in the stomach produce significantly less hydrochloric acid, thereby reducing the amount of B12 that can be absorbed from food. These individuals can still absorb B12 from supplements or B12 fortified foods. The Institute of Medicine recommends that people over 50 take B12 in the form of supplements or fortified foods. Another one to two percent of older people have pernicious anemia, which is characterized by a lack of intrinsic factor in their gastrointestinal tract. Such individuals cannot absorb vitamin B12 well from any source and must get intramuscular injections of B12 or take very high oral doses of vitamin B12.
Vegetarians
Strict vegetarians and vegans are at risk for developing B12 deficiency, because B12 is found almost exclusively in food products derived from animals. VeganHealth.org recommends that all vegetarians eat fortified cereals or take B12 supplements containing at least 10 micrograms of B12. It is especially important for strict vegetarian women, who are pregnant or lactating to take in adequate amounts of B12, because B12 deficiency can result in birth defects. One way to check if your body has enough vitamin B12 stores is to test for blood homocysteine levels. Elevated levels may be due to too little vitamin B12 and higher intake of B12 is indicated.
Reducing homocysteine levels
Elevated homocysteine is a risk factor for heart disease and stroke. Inadequate amounts of vitamin B12 can cause homocysteine levels to rise. Studies have shown that supplementation with B12 by people deficient in the vitamin will reduce homocysteine levels ((Deshmukh, U.S. et al.). In other studies, lowering homocysteine levels by vitamin cocktails containing B12 was not consistently associated with reduced risk of cardiovascular disease.
Sources
http://ods.od.nih.gov/factsheets/vitaminb12.asp
http://www.veganhealth.org/articles/everyvegan/
Deshmukh, U.S. et al. Effect of physiological doses of oral vitamin B12 on plasma homocysteine: a randomized, placebo-controlled, double-blind trial in India. Eur. J. Clin. Nutr. (2010) 64: 495
