Objective: It is unclear whether there is a relationship between lithium administration and folate and vitamin B₁₂ metab olism.

Materials and Methods: We compared retrospectively serum B₁₂, and serum folate concentrations in patients receiving and not receiving lithium at our hospital's Psychiatric Unit between January and December 2008. Serum folate and B₁₂ concentrations were estimated in 64 affective disorder patients taking lithium prophylactically, 42 of whom had bipolar disorder, and in 64 psychiatric patients not receiving lithium, 46 of whom had unipolar depression.

Results: There were no significant differences in serum B₁₂ or folate between lithium-treated and untreated psychiatric patients. There were 5 (8%) patients with serum folate concentrations below 3 ng/mL and 18 (28%) with serum B₁₂ concentrations below 193 pg/mL in lithium-treated patients. 14 patients (21%) had low levels of B₁₂ in non-lithium treated patients.

Conclusion: Contrary to other findings, there were no statistically differences between the folate and B₁₂ concentrations of each group.