VIP and major depressive disorder: Additionally, we found that lower serum VIP levels were detected in the anxiety subgroup and depression subgroup than in the non-anxiety subgroup and non-depression subgroup [(107.45 ± 15.40) pg/ml vs. (116.41 ± 13.67) pg/ml, P < 0.05]; [(104.45 ± 15.26) pg/ml vs. (113.43 ± 14.52) pg/ml, P < 0.05].