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

Consensus Statements on the Treatment, Rapid Correction, Administration, and Monitoring of Vitamin D Deficiency in Adults.

• A serum 25-hydroxyvitamin D [25(OH)D] concentration <20 ng/mL should be considered an indication for treatment.Cholecalciferol (vitamin D3) is recommended for supplementation and treatment.For adults, a typical daily requirement is 800–2000 IU/day.When rapid correction (loading) is not required, a maintenance-oriented regimen of 800–2000 IU/day may be used.If underlying causes of vitamin D deficiency cannot be corrected, long-term maintenance supplementation may be required.In obesity, in patients receiving medications that accelerate vitamin D metabolism (e.g., systemic glucocorticoids and antiepileptic drugs), and in malabsorption syndromes, higher maintenance doses (approximately 3000–6000 IU/day) may be required.In persistent malabsorption, substantially higher doses (e.g., 10,000–50,000 IU/day) may be required; if response remains inadequate, hydroxylated forms of vitamin D may be considered.The tolerable upper intake level for routine daily supplementation in adults is 4000 IU/day.The treatment target is to maintain serum 25(OH)D between 20 and 50 ng/mL.
• A loading regimen is not routinely recommended but may be considered when rapid clinical correction is needed.Loading may be considered in adults with 25(OH)D <20 ng/mL and evidence suggestive of secondary hyperparathyroidism.Situations where rapid correction may be considered include very low 25(OH)D (<12 ng/mL), very high fracture risk in osteoporosis, secondary hyperparathyroidism, and hypocalcemia.Example regimen: 50,000 IU/week for 6–8 consecutive weeks, followed by 800–2000 IU/day maintenance.Alternative regimen: 6000–10,000 IU/day orally for 4 weeks, followed by 800–2000 IU/day maintenance.In obesity or malabsorption, a higher loading regimen (e.g., 100,000 IU/week for 8 weeks) may be considered, followed by maintenance (e.g., 4000–6000 IU/day) based on response.
• Daily and intermittent cumulative regimens (weekly, every two weeks, or monthly) have comparable efficacy and safety when equivalent cumulative doses are used.Capsule, drop, and tablet formulations demonstrate similar efficacy when used at equivalent doses.Parenteral vitamin D should be reserved for selected patients (e.g., severe malabsorption, inability to take oral therapy, or critically ill patients when clinically indicated).A patient-centered regimen incorporating dosing preferences (daily/weekly/monthly) may improve adherence.
• Serum 25(OH)D should be re-measured 8–12 weeks after initiation of treatment.Based on follow-up 25(OH)D concentrations, the regimen should be continued, adjusted, or transitioned to maintenance dosing.If 25(OH)D is within the target range (20–50 ng/mL), the same dose may be continued as maintenance therapy.If serum 25(OH)D is 50–60 ng/mL, concentrations are generally safe but exceed recommended targets; the dose and other sources of vitamin D should be reviewed.If serum 25(OH)D is 60–99 ng/mL (gray zone), the risk of complications may increase with higher concentrations; the regimen should be reviewed. Vitamin D can be stopped for 2–3 months; reconsider after measurement of 25(OH)D concentrations.If serum 25(OH)D is ≥100 ng/mL, it is defined as hypervitaminosis D; vitamin D intake should be stopped for at least 3 months, and clinical and biochemical evaluation should be undertaken.If serum 25(OH)D is ≥150 ng/mL, vitamin D intoxication (toxicity) should be considered. Vitamin D should be stopped for at least 3 months. Serum calcium levels should be measured and closely followed up.