Best Practice Recommendations for the Assessment, Prevention and Treatment of Vitamin D Deficiency in Türkiye: A 2026 Update in a Setting with Limited Mandatory Food Fortification

Background: Vitamin D deficiency is a common global health problem and remains highly prevalent in Türkiye, where limited food fortification and heterogeneous clinical practices contribute to variability in testing and supplementation strategies. Aims: To provide Türkiye-specific best practice recommendations for defining clinically relevant serum 25-hydroxyvitamin D [25(OH)D] thresholds, identifying adult risk groups for targeted testing, and recommending evidence-based prevention, treatment, and monitoring approaches while minimizing under-treatment and inappropriate high-dose use. Methods: This national expert consensus document was developed by endocrinologists from across Türkiye using a structured, modified Delphi methodology. Draft statements informed by systematic literature reviews were rated via online surveys using a 9-point Likert scale, followed by two Delphi rounds and a face-to-face consensus meeting in İstanbul in October 2025. Results: Recommendations addressed sun exposure, laboratory assessment, screening, supplementation, treatment, and follow-up. Serum 25(OH)D <20 ng/mL was defined as deficiency and <12 ng/mL as severe deficiency, with a target range of 20–50 ng/mL. Routine population-wide screening was not recommended; instead, targeted testing in high-risk adults and symptom-driven biochemical evaluation were endorsed. Empiric supplementation was recommended for selected high-risk groups, with cholecalciferol as the preferred agent. Higher individualized doses were suggested in obesity or malabsorption, while loading regimens were reserved for specific clinical indications, such as severe deficiency or certain medical conditions that impair vitamin D metabolism. Reassessment of 25(OH)D at 8–12 weeks was recommended. Conclusion: These consensus-based recommendations provide a practical, context-specific framework for assessing, preventing, treating, and monitoring vitamin D deficiency in adults in Türkiye.