Comparison of vitamin B12, vitamin D and folic acid blood levels in patients with schizophrenia, drug addiction and controls

•No study has compared vitamin deficiencies in schizophrenia (SCH), substance use disorder (SUD).•Vitamin deficiencies were widespread in SUD and SCH in this study.•B12 deficiencies were more common in SCH, and folic acid deficiencies were more prevalent in SUD.•Interestingly, the SUD group had the highest vitamin D levels even including control group.•The rates of vitamin deficiencies were strikingly high in all the groups. Schizophrenia (SCH) and drug addiction are chronic disorders that are frequently accompanied by physical diseases, poor nutrition and reduced self-care, all of which are likely to result in vitamin deficiencies. The objective of this study was to compare vitamin levels in SCH patients, substance use disorder (SUD) patients and healthy controls (HCs). The study included 189 SCH patients, 119 SUD patients and 109 HCs. Information on vitamin B12, folic acid and vitamin D levels were retrieved from the hospital’s database, and mean values and deficiency/insufficiency were evaluated. Vitamin D deficiency (