The increased total score of ESS (β = 0.004; P = 0.033) and increased probabilities of daytime sleepiness in four different situations (sitting inactive in public places (β = 0.036; P = 0.048) (Fig. 7A), sitting and talking to someone (β = 0.031 ; P = 0.032) (Fig. 7B), sitting quietly after lunch (β = 0.030; P = 0.016) (Fig. 7C), stopped in traffic in a car (β = 0.033; P = 0.021) (Fig. 7D)) had significant correlations with a notable rise increase in serum NfL levels in PD females, whereas no associations were found in total PD participants and PD males (Supplementary Table S13). Here, NEFL is linked to Parkinson disease.