Figure 3. Differential urinary metabolites between the different groups. (A) 18 differential metabolites between young HCs and young MDD patients; (B) 15 differential metabolites between middle-aged HCs and middle-aged MDD patients; (C) eight and five metabolites were only altered in young and middle-aged MDD patients, respectively, and 10 metabolites were altered in both young and middle-aged MDD patients.