It has been hypothesized that lowered antioxidant capacity, which leads to increased oxidative stress, may be involved in the pathophysiology of major depressive disorder (MDD) and anxiety disorders and might be altered by antidepressant treatment.

This study investigated the association of plasma uric acid, the greatest contributor to blood antioxidant capacity, with MDD, generalized anxiety disorder, social phobia, panic disorder, agoraphobia and antidepressants in a large cohort.

Data was derived from the Netherlands Study of Depression and Anxiety including patients with current (n = 1648) or remitted (n = 609) MDD and/or anxiety disorder(s) (of which n = 710 antidepressant users) and 618 controls. Diagnoses were established with the Composite Interview Diagnostic Instrument. Symptom severity was ascertained in all participants with the Inventory of Depressive Symptoms and the Beck Anxiety Inventory. ANCOVA and regression analyses were adjusted for sociodemographic, health and lifestyle variables.

Plasma uric acid was lower in those with current MDD and/or anxiety disorder(s) (adjusted mean 270 μmol/L) compared to those with remitted disorders (280 μmol/L, P < 0.001) or to controls (281 μmol/L, P < 0.001; Cohen's d 0.14). Within patients antidepressants were not associated with uric acid levels. Increasing symptom severity was associated with lower uric acid levels for both depression (β = –0.05, P = 0.001) and anxiety symptoms (β = –0.05, P = 0.004).

This large scale study finds that the antioxidant uric acid is lower in current, but not remitted, MDD or anxiety disorders and in persons with higher symptom severity, suggesting disturbances in redox homeostasis play a role in the pathophysiology of depression and anxiety disorders.

The authors have not supplied their declaration of competing interest.