EDN1 and insomnia: Notably, prior to adjusting for multiple testing, a significant negative association between insomnia severity and serum endothelin-1 levels (b = −0.019; 95% CI [−0.037, −0.002]; β = −0.183; unadjusted p = 0.033; adjusted p = 0.528; R2 = 0.119) was found, and the significant positive association with serum acetyl-L-carnitine levels observed in the univariate analyses remained significant after controlling for relevant covariates (b = 0.036; 95% CI [.000, 0.073]; β = 0.167; unadjusted p = 0.049; adjusted p = 0.528; R2 = 0.134).