twelve deficiency, is an independent vascular risk factor associated with cerebral microvascular disease. 31 Cerebral microangiopathy is considered to be the basis for vascular dementia. High homocysteine (HY) levels may also lead to an excessive production of homocysteic acid and cysteine sulphinic acid, which act as endogenous agonists of N-methyl- d – aspartatate receptors and may impair cognitive functions by excitotoxic mechanisms (see review 32 ).
Vitamin B12 is contained in a wide variety of animal proteins. After intestinal absorption it enters enterohepatic circulation. The reported body half-life exceeds 1,300 days. With normal absorption, the recommended daily intake ranges from 2 ?g to 5 ?g. 10,33 Malnutrition as a sole cause is rare and occurs in cases of chronic alcoholism, extreme vegetarianism, and other forms of insufficient dietary supply. 33 Intestinal absorption of vitamin B12 depends on a series of steps including the liberation of protein-bound vitamin B12 from proteins by gastric acid 34 and its transfer to intrinsic factor produced by gastric parietal cells. Loe edasi »