NK cells: Natural Killer Cells; ROS: Reactive Oxygen Species; TNF-α: Tumor Necrosis Factor Alpha; IL-6: Interleukin 6; IL-10: Interleukin 10; BDNF: Brain-Derived Neurotrophic Factor; NF-κB: Nuclear Factor Kappa-Light-Chain-Enhancer of Activated B Cells; HPA Axis: Hypothalamic–Pituitary–Adrenal Axis; ACh: Acetylcholine; T3: Triiodothyronine; T4: Thyroxine; GABAergic: Refers to Gamma-Aminobutyric Acid-Mediated Neurotransmission; Nrf2: Nuclear Factor Erythroid 2-Related Factor 2; HO-1: Heme Oxygenase 1; IgA: Immunoglobulin A; MCI: Mild Cognitive Impairment. This evidence concerns the gene BDNF and Cognitive impairment.