Vitamin B12 is a water-soluble vitamin needed for normal nerve cell activity, DNA replication, and production of the mood-supporting substance SAMe (S-adenosyl-Lmethionine).* Vitamin B12 acts with folic acid and vitamin B6 to control homocysteine levels.

As we age, our absorption of vitamin B12 decreases, and some studies suggest that the elderly could benefit from 10-25mcg of B12 daily. One study of the elderly suffering from B12 deficiency even suggested that up to 500-1000mcg of B12 daily might be necessary to achieve optimal B12 levels; this was tested via a highly accurate plasma methylmalonic acid concentration test.
Supplementation with B-12 Intrinsic Factor:

Supports nervous system health*
Supports red blood cell production*
Supports energy*
Supports metabolism of fats and carbohydrates*