The water-soluble vitamin B12 is important for DNA synthesis, brain development, red blood cell formation and a wide range of cellular processes. Vitamin B12 contains the metal ion cobalt and is only produced by bacterial cells present in animals, not by plants. The Linus Pauling Institute at Oregon State University estimates that 10 to 15 percent of people over 60 have a vitamin B12 deficiency.
Symptoms
Someone with a vitamin B12 deficiency may feel fatigued or weak. Loss of appetite, anemia, weight loss and constipation are also symptoms of a lack of B12. Deficient individuals may also experience tingling or numbness of the hands or feet. They may become confused or depressed and may experience memory problems, a loss of balance and mouth soreness. Babies with a B12 deficiency may exhibit slow growth and delayed development. Parents and physicians may also note motor disorders and anemia in an affected infant.
Diagnosis
Diagnosis of a B12 deficiency is typically made by checking serum levels of the vitamin after suspicious symptoms are noted by a physician. Serum levels of this vitamin should be above 200 picograms per milliliter in normal individuals. Other blood tests that look at homocysteine levels and methylmalonic acid levels may also indicate a possible B12 deficiency. If either of these substances is found at high levels in the blood, further tests may be ordered to determine whether a lack of B12 is the cause.
Treatment
The standard treatment for a B12 deficiency is a daily injection of the vitamin at a dose of 100 to 1,000 mcg for one to two weeks followed by injections of 1,000 mcg every one to three months. Another option is high doses of oral B12 supplements. According to the NIH Office of Dietary Supplements, oral treatment can be taken as a daily dose of 1,000 to 2,000 mcg, gradually changing to a 1,000 mcg dose every week and eventually slowing to 1,000 mcg monthly until serum vitamin B12 levels are back to normal. Neurological symptoms may be irreversible even with treatment.
Causes and Risk Factors
In many cases, the cause of a B12 deficiency remains unknown, but low dietary intake of this vitamin is a probable cause. Malabsorption disorders that prevent the uptake of vitamin B12 and the autoimmune disease pernicious anemia may also lead to a deficiency. Older people are at risk for a condition called atrophic gastritis, which lowers hydrochloric acid in the stomach and prevents vitamin B12 utilization. Some gastrointestinal disorders, such as Crohn's disease, may also affect absorption of B12. Strict vegetarians may be at higher risk than other populations because B12 is primarily available through animal sources.
Concerns
Individuals with a high intake of folate, or its synthetic form folic acid, may have undiagnosed vitamin B12 deficiency because folate can mask symptoms of this disorder. In articular, the anemia associated with vitamin B12 deficiency is hidden by the presence of folate, even though the deficiency may be causing neurological damage. Daily folic acid intake of more than 1,000 mcg can cause this problem.
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