HHcy is considered a risk factor for AD, as it affects processes such as DNA methylation and repair, oxidative stress, amyloid β aggregation, tau phosphorylation, vascular endothelial dysfunction, and the secretion of inflammatory mediators like tumor necrosis factor α (TNFα), nuclear factor κB, interleukin 6 (IL-6), and interleukin 8 (IL-8) [86]. Here, TNF is linked to Alzheimer disease.