A follow‐up study with a double‐blinded, randomized controlled vitamin D supplementation trial in patients with major depressive episode (<scp>DepFuD</scp>): A study protocol and baseline characteristics

Promising initial studies on vitamin D (VD) supplementation as an adjunct treatment for major depressive disorder (MDD) require rigorously designed randomized controlled trials (RCTs). We aim to investigate the effects of augmenting standard MDD treatment with VD supplementation and examine factors influencing the treatment outcome. This article describes the study design, measures, and baseline characteristics. This multicenter RCT compares the efficacy of a six-month VD intervention at 100 micrograms/day versus 10 micrograms/day (μg/day) (4000 IU (international units)/day vs. 400 IU/day) added to a standard treatment in outpatients aged 20-61 years with MDD. The primary outcome is change in the Montgomery-Åsberg Depression Rating Scale (MADRS) score. Secondary outcomes are other indicators of mental health and functionality (BDI, SOC, 15-D, PSS10, LS-4, LOT-R, YSQ-S2-extended, CORE-OM, TAS-20, BRCS, TADS, SCL-90, DIAD, GAF), and circulating biomarkers. Intervention assessments are conducted at baseline, 3, and 6 months, and follow-ups at 18 months and 6 years post-baseline. The baseline sample had 319 subjects (74% women; median age 31 (inter-quartile range (IQR) 15), mean MADRS score 21.38 (SD 6.04)), with 281 assigned to the RCT. At present, the study continues as a follow-up study. DepFuD project will provide extensive information regarding the potential benefits of VD and enables to identify various biopsychosocial depression-associated risk factors.