National food surveys indicate that the median daily intake of vitamin B12 in the United States by men is approximately 5 micrograms and the median intake of women is about 3.5 micrograms—well within the recommended levels. B12 is not recommended for children.
There are, however, a number of conditions that may cause deficiencies of vitamin B12. Individuals who suffer from malabsorption syndrome will most likely need extra vitamin B12. Diseases/conditions requiring supplementation under a doctor’s care include post stomach surgery, pernicious anemia, post gastric bypass surgery, Crohn’s disease, and HIV patients with chronic diarrhea. Treatment usually involves monthly intramuscular injections of 100 micrograms of vitamin B12. In addition, the National Academy of Sciences has recommended that individuals over the age of 50 meet their RDA by consuming foods fortified with the synthetic form of B12 or a supplement containing vitamin B12.
Vitamin B12 and Pernicious Anemia
Vitamin B12 requires an “intrinsic factor”—a compound made inside the body—for
absorption from the intestinal tract into the bloodstream. This intrinsic factor is made in the stomach, where it attaches itself to the vitamin and carries it to the small intestine to be absorbed.
Certain people have a defective gene for intrinsic factor in their genetic makeup, so they can’t make it in their bodies. This defect usually becomes evident in midlife. If the intrinsic factor is missing, vitamin B 12 cannot be absorbed from the diet and deficiency
occurs. When this happens, or when the stomach has been injured and cannot produce enough intrinsic factor, B 12 must be provided via injections in order to bypass the stomach.
Vitamin B12 deficiency, or pernicious anemia, is a type of anemia characterized by large, immature red blood cells identical to those seen in folate deficiency. Symptoms include decreased energy and exercise tolerance, shortness of breath, fatigue, and palpitations. Left untreated, pernicious anemia can lead to a creeping paralysis of the nerves and muscles that begins at the extremities and works up the spine.
Although the symptoms—including the paralysis—can be reversed with vitamin B12 treatment, the anemia can be misdiagnosed as a folate deficiency. Folic acid supplements will correct the anemia, but not the damage to the nervous system. For this reason, people over the age of 50 who take folic acid supplements should also take at least 25 micrograms of B12 per day, since excess folic acid could mask a potential B12 problem.
It is estimated that 10 to 30 percent of people over the age of 50 may develop vitamin B12 deficiency due to an inability to absorb the naturally occurring form of B12 found in food. Why? Many older people have inadequate gastric (stomach) acid production, which can limit the amount of vitamin B12 absorbed. They can, however,
absorb synthetic forms of the vitamin, which are found in fortified foods and supplements.
