Background: There are prior evidences in regard to the relationship between folate deficiency and depressive disorders,whichemphasizedthe importance of vitamin B12 and folate in carbon transfer metabolism required for the production of serotonin. It is indicated that vitamin B12 and folic acid levels can be related to certain neuropsychiatric disorders like Obsessive-compulsive disorder (OCD).

Aim: To compare vitamin B12 and folic acid serum levels in patients with obsessive-compulsive disorder versus healthy group.

Methods: This was a cross sectional study, which was performed on patients with OCD during October 2018 to August 2019, referred to Imam Reza and Ibne-Sina hospital's clinics. Patients who were diagnosed with OCD according to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) criteria were approached and informed about the aims and methods of the study. We evaluated the serum level of Vitamin B12 and folate and compared it between OCD patients and healthy control groups.

Results:Thirty two patients in each group were evaluated. The mean age of them was 37.14± 11.00 years old (20- 68). Twenty one patients were male (32.8%) and others were female. Vitamin B12 deficiency was significantly higher in OCD patients in comparison with control group (24 patients (75%) versus 14 patients (43.75%); P=0.011). However, folate deficiency was not significantly different between two groups (9.37% in OCD group versus 12.5% in control group; P=0.68). there was significant negative correlation between severity of OCD and level of vitamin B12 level (r=-0.301, P=0.016).

Conclusion: Our study showed that there is significant vitamin B12 deficiency in patients with OCD that is negatively correlated with severity of disease. Therefore, using vitamin B12 supplements in patients resistant to routine treatment can be helpful.

Keywords: Obsessive-compulsive disorder, vitamin B12, folate