NEFL and major depressive disorder: The NfL plasma levels were significantly and positively correlated with age in the whole cohort (r (30) = 0.657, p-value < 0.0001) and also in both the HC (r (15) = 0.740, p-value = 0.002) and the MDD group (r (14) = 0.608, p-value = 0.018).