Vitamin D Deficiency Associated With Cognitive Functioning in Psychotic Disorders

Background: Cognitive dysfunctions are core features of psychotic disorders with substantial impact on daily functioning. Vitamin D deficiency has been found to be related to cognitive dysfunctions, but the associations between vitamin D deficiency and cognition in persons with a psychotic disorder are largely unknown.

Methods: This cross-sectional study included 225 patients with a DSM-IV psychotic disorder consecutively recruited from 2003 to 2014 and 159 randomly selected healthy controls, assessed by a cognitive test battery, a clinical protocol (including Structured Clinical Interview for DSM-IV Axis I Disorders and Positive and Negative Syndrome Scale), and a physical examination including vitamin D measurements. Multiple regression models were performed to evaluate the effect of vitamin D deficiency (defined serum 25-hydroxyvitamin D [25(OH)D] < 25 nmol/L) on key cognitive domains: processing speed, verbal learning, verbal memory, and executive functioning.

Results: Vitamin D deficiency was significantly associated with decreased processing speed (ie, Digit Symbol Coding) (t = −2.6, P = .01; total model: adjusted R2 = 0.40, F6, 374 = 43.8, P < .001) and decreased fluency (ie, verbal fluency) (t = −2.1, P = .04; total model: adjusted R2 = 0.35, F6, 373 = 34.2, P < .001) when the results were controlled for age, ethnicity, IQ, patient versus control status, and substance or alcohol abuse. Additional analyses indicated that negative symptoms diluted the association between vitamin D deficiency and processing speed (t = −1.72, P = .09) and verbal fluency (t = −1.35, P = .18) in patients.

Conclusion: The associations between vitamin D deficiency and processing speed and verbal fluency are good arguments for planning large-scale randomized controlled studies in target populations so conclusions can be made about the potential beneficial effect of vitamin D on cognition in psychotic disorders.