 Mild vitamin B12 deficiency is highly prevalent in old age. Reasons for this high prevalence are not fully understood, but include atrophic gastritis and bacterial overgrowth which affect the absorption active of food-bound vitamin B12. In contrast, the ability to absorb crystalline vitamin B12 e.g. the form found in fortified foods or vitamin pills remains intact in old age. In both healthy and cognitively impaired elderly people, associations between vitamin B12 status and cognitive performance have been observed, and the follow-up of geriatric patients suggests effects of parenteral treatment in early cognitive impairment. 