The invention pertains to the use of a preparation for the manufacture of a composition for preventing or treating impaired plasma levels of one or more polar lipids such as phosphatidylcholines [PC] selected from the group consisting of phosphatidylcholine diacyl C36:6 [PC aa C36:6], phosphatidylcholine diacyl C38:0 [PC aa C38:0], phosphatidylcholine diacyl C38:6 [PC aa C38:6], phosphatidylcholine diacyl C40:6 [PC aa C40:6] and phosphatidylcholine acyl-alkyl C40:6 [PC ae C40:6] in a preclinical AD or MCI subject or a subject with a high likelihood of developing AD or MCI, and wherein said subject is administered with a composition comprising at least one, preferably at least two, most preferably all B vitamins selected from the group consisting of vitamin B6, vitamin B12 and vitamin B9.
