Serum and red blood cell folate in depression.

Serum folate concentrations were estimated in patients with major depressive disorders, lithium-treated patients, detoxified alcoholic patients and normal controls. Red blood cell (RBC) folate concentrations were also estimated in subgroups of patients with major depressive disorder and normal controls. Results showed significantly lower serum and RBC folate concentrations in patients with major depressive disorder than in normal controls. Lower serum folate concentrations were associated with greater severity of depression. There was no association between serum and RBC folate concentrations and endogenicity of depression or the presence of weight loss.