- Vitamin B 6 plays an essential role in the normal functioning of the central nervous system. Normal homocysteine (Hcy) serum level is maintained by remethylation of Hcy to methionine by enzymes that require folic acid and vitamin B 12 and by catabolism to cysteine by a vitamin B 6 -dependent enzyme. These findings may be consistent with the hypothesis that the vitamin B 6 status may influence plasma Hcy levels. The aims of this preliminary study were (1) to determine whether a correlation exists between Hcy and vitamin B 6 levels in patients with schizophrenia and schizoaffective disorders and (2) to investigate whether treatment with high-dose vitamin B 6 may reduce Hcy levels in these patients. Methods: In this preliminary study, we enrolled 11 patients with schizophrenia or schizoaffective disorders (7 men and 4 women; mean age ± SD, 50 ± 12 years) receiving high doses of vitamin B 6 treatment (1200 mg/d) for 12 weeks. Blood samples for the assessment of pyridoxal-5-phosphate and Hcy serum levels were obtained at baseline and after 12 weeks of treatment. Results: Age was significantly positively correlated with Hcy levels at baseline (r = 0.392, P = 0.004). All other parameters, including diagnosis, disease duration, and pyridoxal-5-phosphate serum level, were not correlated with Hcy serum levels at baseline. After vitamin B 6 treatment, Hcy serum levels significantly decreased (14.2 ± 3.4 vs. 11.8 ± 2.0 (μmol/L, respectively, t = 2.679, P = 0.023); this decrease being statistically significant in men but not in women. Conclusions: High doses of vitamin B 6 lead to a decrease in Hcy serum level in male patients with schizophrenia or schizoaffective disorder.