A severe B12 (cobalamin) deficiency will eventually result in anemia if uncorrected. Anemia refers to an insufficient number of healthy red blood cells, which impairs the ability of oxygen to be carried to your body’s tissues. Pernicious anemia – the type caused specifically by cobalamin deficiency – can gravely impair neurologic function. Subclinical deficiency is much more common, in which a low cobalamin level appears on a blood test, but has yet to cause anemia.
Recall from my previous post on vegetarian diets that absorption of vitamin B12 is dependent on intrinsic factor (IF), which is produced in the gut. Causes of deficiency include inadequate dietary intake and impaired intestinal malabsorption, possibly due to lack of IF or insufficient gastric acid secretion (as is the case in the elderly). If your blood labs do not improve after dietary manipulation or supplementation, speak with your doctor about other tests that can determine if your deficiency is related to malabsorption.
The severity of your B12 deficiency dictates the level of supplementation required. A B12 level less than 400 pg/mL may be cause for concern, but it’s all about lab value trends. Correction of vitamin B12 levels to within the acceptable range may simply require a daily multivitamin (that usually contains 6 µg per tablet). The recommended daily intake for American adults is 2.4 µg. Research shows that for people (like vegetarians) who have normal B12 absorption, doses greater than 5 µg per day exceed the binding capacity of IF and only a tiny fraction can be absorbed anyway.
On the other hand, a more critical deficiency may require several weeks of high-dose supplementation (e.g. 1,000 µg daily oral dose) to be taken under the direction of your doctor. Sublingual B12 supplements, which dissolve under your tongue, are very effective in delivering the nutrient directly to your bloodstream, similar to an injection. These oral supplements come in 1,000 or even 5,000 µg doses or more! “Mega-dosing,” however, is excessive for someone who is still only moderately low in B12. While no toxic level of B12 supplementation has been found to date, it’s always wise to stick with the lowest dose possible that will effectively achieve healthful results.