APOE and Mental deterioration: Folate is important in one-carbon metabolism, and methylation reactions involving folate may be important in the formation and maintenance of neuronal and glial membrane reactions.17 Most longitudinal studies have found associations between folate and cognitive decline,18-20 but one study did not.7 In our study, this association was not explained by other potential confounding factors, such as disability, vascular risk factors, and APOE genotype.