Vitamin B12 is a water-soluble vitamin found mainly in animal products and fortified foods. Its absorption is a complex process which depends on a compound produced by the stomach called intrinsic factor. Some people may present a genetic defect that disables the body from producing this compound, which significantly impairs vitamin B12 absorption, leading to its deficiency.
Vitamin B12 plays important roles in the maintenance of nerve cells, formation of red blood cells, and synthesis of genetic material. It also participates in folate metabolism, meaning that the lack of vitamin B12 may cause folate deficiency as well. In addition, vitamin B12 together with folate and vitamin B6 remove homocysteine (a protein-related compound that is associated with blood clot formation and arterial wall damage) from the bloodstream, preventing its toxic buildup. Thus, low intakes of these B vitamins may increase the risk of cardiovascular disease.
Vitamin B12 deficiency is unlikely to occur in healthy people who consume animal products regularly. The great majority of cases of deficiency are attributed to defective absorption rather than inadequate intake. However, vegans who exclude meat, dairy products and eggs from their diets may be at risk. They should look for alternative sources such as fortified cereals and beverages, or consider supplementation. Also, older adults may develop an inability to produce gastric acid which hampers the body’s ability to use vitamin B12. This population is encouraged to have regular physical examinations that test for vitamin B12 deficiency.
The lack of vitamin B12 causes nerve degeneration, which may progress to paralysis of nerves and muscles. In addition, vitamin B12 deficiency impairs folate function on red blood cell formation, leading to anemia. Symptoms of deficiency include weakness, sore tongue, back pain, apathy, and tingling in the extremities. Nerve damage symptoms may take over three years to manifest, but when nerve destruction occurs, it is irreversible; thus, it is important to receive early diagnosis and treatment.
This vitamin is abundant in animal products including meat, poultry, seafood, milk and dairy products, and eggs. It may also be found in enriched foods and beverages such as ready-to-eat cereals and soy drinks. The Recommended Dietary Allowance (RDA) of vitamin B12 for adults is 2.4 micrograms per day. Most adults tend to consume twice that much, making dietary deficiency unlikely. However, because the aging process may reduce absorption capacity, people over 50 years old are advised to meet their RDA by consuming fortified foods or taking supplements containing the crystalline form of vitamin B12[1].
References
Boyle, M. and Long, S. Personal Nutrition. Belmont, CA: Wadsworth Cengage Learning. 2010.
Wardlaw, G. and Smith, A. Contemporary Nutrition. New York: McGraw-Hill. 2009.