(4) BMI: The U-shaped delirium risk (optimal range 18.5–24.9 kg/m2 (Feinkohl et al., 2023)) reflects dual mechanisms: low BMI exacerbates catabolism (neurotransmitter precursor deficiency), while obesity induces leptin resistance (insulin resistance/BBB disruption). This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.