Moreover, serum and plasma IL-6 levels were found to be significantly higher in FE DN individuals and medication-free MDD patients, compared to HCs [56,57], and a previous meta-analysis on the FE DN group confirmed these findings (g = 0.62; 95% CI, 0.17 to 1.06; p = 0.007; I2 = 85%) [17]. Here, IL6 is linked to major depressive disorder.