Background/ objectives <p>Diabetes distress (DD) is significant emotional reactions to the diagnosis, threat of complications, self-management demands, and unsupportive social structures. Vitamin D (VitD) supplementation benefits various mood disorders but its role on DD remained unproven. We aim to study the effect of VitD supplementation on DD among patients with VitD deficiency.</p> Method <p>This was a prospective, open-label randomized intervention study conducted in Putrajaya Hospital using validated Diabetes Distress Scale 17 (DDS17). The DDS17 addresses four subdomains – A (Emotional burden), B (Physician-related distress), C (Regimen distress) and D (Interpersonal relationship distress). Mean score ≥ 2 is considered DD worthy of clinical attention. Convenience sampling was adopted followed by simple randomization into intervention or control arm. Outcome measures are collected prospectively at baseline and after 16 weeks of study duration.</p> Results <p>There were 80 participants (71.3% female, 71.3% Malay) with mean age of 47.9 years recruited. Baseline demographic and diabetic profiles showed no significant difference between arms. VitD improved from 25.3nmol/L to 56.8nmol/L in intervention arm (<i>n</i> = 40) while participants in control arm (<i>n</i> = 40) remained VitD deficient at 37.6nmol/L. Mean total distress score in intervention arm improved from 2.9 to 1.7 (<i>p</i> &lt; 0.01). Significant improvement was noted between group for total DD (<i>p</i> = 0.027), emotional distress (<i>p</i> = 0.043) and regimen distress (<i>p</i> = 0.030). Significant DD improvement was found across all subdomains in the intervention arm regardless of baseline VitD level but no significant improvement in control arm participants with baseline VitD &lt; 25nmol/L.</p> Conclusion <p>Adequate VitD supplementation is effective to improve DD, thus warrants consideration for people living with diabetes and VitD deficiency.</p>