These results imply that lower serum folate or vitamin B12 status might expose subjects with MTHFR 1793 G/A genotypes to cognitive decline (especially, with the abilities of name, attention, abstraction and orientation), while, for the subjects with higher serum folate and vitamin B12 levels, the association of MTHFR 1793 G/A genotypes on cognitive function was undetectable. This evidence concerns the gene MTHFR and Mental deterioration.