"Elevated folate level and vitamin B12
How increased folate level influences neurological disorders related to vitamin B12 deficiency is a potential issue in relation to mandatory folic acid fortification. Vitamin B12 is a critical coenzyme for methionine synthase (MS), and is related to folate metabolism via the action of methionine biosynthesis. Therefore, insufficiency may interrupt the conversion of 5-CH3H4PteGlu to H4PteGlu (folate-trap) (108). Furthermore, in CNS tissue, MS dependant Hcy-methylation is the sole pathway for methionine production (no betaine is involved in the pathway in this tissue) (109).during purine and pyrimidine synthesis even with impaired MS, and folate therapy may seem to be effective in improving the symptoms of vitamin B12deficiency, while neurological lesions progress (112). For these reasons, elevated intake of folate (PteGlu) may potentially mask vitamin B12 deficiency and prevent early diagnosis of symptoms (megaloblastic anaemia), leading to a late diagnosis when neurologic sequelae have already occurred. This condition -pernicious anaemia- involves demyelinations and is irreversible (111).
A decline in cognition in the elderly is another potential issue of vitamin B12 related to mandatory folic acid fortification (113). Morris et al. (114) suggested that participants with a high intake of folate combined with low blood vitamin B12 showed faster cognitive decline, compared to a group with high folate intake and high total vitamin B12 intake. A report containing three Australian cohorts also suggested impaired cognitive performance in the elderly group with combined low serum vitamin B12 and high red cell folate (115).
10 to 15% of the elderly population (over 60 years) are not taking sufficient vitamin B12 (116), and the low level of blood vitamin possibly stems from many reasons including, lack of intrinsic factor, atrophic gastritis and other gastrointestinal issues (Crohn’s and celiac disease) as well as drug and alcohol consumption (102). The prevalence of low serum vitamin B12 in the absence of anaemia and macrocytosis has not changed since the implementation of mandatory folic acid fortification in the US (117."