Nutritional deficiencies are common in the elderly. Perhaps 10 to 20 percent of dementias in the elderly are reversible, and malnutrition is an important cause of reversible dementia. In addition to inadequate nutrient intake, other factors — such as impaired nutrient absorption through the gut lining — contribute to the deficient nutriture. (1) As an example of nutritionally-caused dementia, we will review the contribution of the vitamin B complex.

Vitamin B12

A deficiency of vitamin B12 is one of the most common nutritional causes of reversible dementia. Although a B12 deficiency is also associated with a megaloblastic (enlarged red blood cell) anemia, the vitamin may be deficient even in the absence of anemia or macrocytosis.

To evaluate the possibility of a vitamin B12 deficiency by lab testing, see if a macrocytic anemia is present and if the neutrophils are hypersegmented. While the serum cobalamin level should be measured, the vitamin may still be deficient even if the serum level is at the low end of the normal range. (2) Inactive cobalamin analogs may be included when serum cobalamin is measured using the popular radioisotope dilution method, so a microbiological assay is preferable. (3)

Other useful lab tests include measurements of serums levels of methylmalonic acid and homocysteine, two metabolites of vitamin B12-dependent pathways which are highly sensitive indicators of deficiency. (4) Finally, serum folate levels should also be measured.

As with all vitamin deficiency syndromes, there is a spectrum of severity ranging from the often isolated findings of marginal deficiency to the full deficiency syndrome. Since the B12 deficiency syndrome includes neurologic deterioration, neurologic findings in a person with dementia should raise the index of suspicion and encourage more complete laboratory testing.

When adequate laboratory testing is unavailable, consider a trial of supplementing vitamin B12 by injection, say 1000 mcg IM twice weekly for several weeks. Even if the injection of vitamin B12 is ‘a shot in the dark,’ it is both safe and inexpensive.