NEFL and Alzheimer disease: With regards to plasma AD biomarkers, older age was associated with elevated levels of NfL (t(87) = 8.03, P < 0.0001), GFAP (t(87) = 5.31, P < 0.0001), p-tau181 (t(79) = 2.58, P = 0.01), and with lower values of Aβ42/40 ratio (t(87) = -3.13, P = 0.002).