Vitamin B12, or cobalamin, is a large, complex molecule and one of eight compounds classified as a B vitamin. B-12 is required primarily for higher brain functions and red blood cell production, although its functions overlap with those of folic acid. B-12 deficiency is difficult to determine, although circulating levels in the blood can be a good indicator. B-12 deficiency symptoms are frequently misdiagnosed and are similar to those of Alzheimer's disease.
Functions of B-12
B-12 is required for the synthesis of DNA during cell division, the normal development of red blood cells within bone marrow and for higher brain functions, such as cognition and short-term memory, according to "Vitamins: Fundamental Aspects in Nutrition and Health." Regarding brain function, B-12 is needed to produce myelin, the insulative fatty-acid sheath surrounding neurons that allows for fast transmission of electrical signals generated by the brain. B-12 also protects the brain from shrinkage, which can lead to a host of impairments.
Low Levels of B-12
According to "Human Biochemistry and Disease," B-12 blood levels below 200 picograms per milliliter are indicative of deficiency, although symptoms can take up to five years to develop. B-12 is water-soluble, but unlike most of the B vitamins it can be stored in the body for long periods. Further complicating the matter is folic acid, or vitamin B-9, which is involved in many of the same functions as B-12. Supplementing with folic acid can mask a B-12 deficiency.
Recommended Daily Allowance
The recommended daily allowance for B-12 ranges from 0.4 micrograms in infants to 2.8 micrograms for lactating females, according to "Advanced Nutrition: Macronutrients, Micronutrients and Metabolism." Adult males require 2.4 micrograms daily. The problem with B-12 is that it is not absorbed very well and depends on the presence of intrinsic factor within the intestines. For example, consuming 500 micrograms of supplemental B-12 can result in absorption of as little as 1.8 micrograms, according to "Biochemistry of Human Nutrition." To increase absorption and fulfill requirements, some health care practitioners recommended taking 1,000 micrograms of sublingual B-12, which is designed to quickly dissolve under the tongue.
B-12 Deficiency Symptoms
Insufficient dietary intake of B-12 combined with inadequate stores eventually leads to deficiency symptoms. Vegetarians who avoid beef, poultry, fish and dairy products are at higher risks, as are those who lack intrinsic factor. Symptoms of B-12 deficiency include peripheral neuropathy, such as tingling, numbness and weakness in the limbs; impaired brain function, such as short-term memory loss and cognitive deficits; and macrocytic anemia, which also is known as megaloblastic or pernicious anemia and is characterized by abnormally large, immature red blood cells that do not carry oxygen or carbon dioxide efficiently. According to "Biochemical, Physiological and Molecular Aspects of Human Nutrition," low levels of B-12 also have been associated with asthma, depression, tinnitus and low sperm counts.
References
- "Vitamins: Fundamental Aspects in Nutrition and Health"; G. Combs; 2008
- "Human Biochemistry and Disease"; Gerald Litwack; 2008
- "Advanced Nutrition: Macronutrients, Micronutrients, and Metabolism"; Carolyn D. Berdanier; 2009
- "Biochemistry of Human Nutrition"; George Gropper; 2000
- "Biochemical, Physiological and Molecular Aspects of Human Nutrition"; Martha Stipanuk; 2006
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