Evidence suggests that higher circulating concentrations of methionine cycle metabolites (homocysteine, methionine, and S-Adenosylmethionine) are associated with greater cognitive decline in people with mild cognitive impairment.[1] Since folate and vitamin B12 regulate methionine metabolism and can reduce plasma homocysteine concentrations,[2] it is possible that their intake may influence cognitive decline. However, while lower folate and B12 concentrations are associated with poorer cognitive function,[3][4][5] current evidence does not show that dietary folate or vitamin B12 intake prevents or treats mild cognitive impairment.[6][7][8]
Other cohort studies show that consuming a mediterranean diet[9][10] and a higher dietary intake of omega-3 fatty acids[11] are associated with a lower risk of mild cognitive impairment. Long-duration randomized controlled trials are needed to prove the causality of these associations.