Vitamin D guidelines (Turkey) - May 2026

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

Nutrients 2026, 18, 1665 https://doi.org/10.3390/nu18111665

Dilek Gogas Yavuz h* , Omercan Topaloglu 2, Mutlu Günes 3 , Alper Gürlek 4, Ayse Kubat Üzüm 5 ,Zafer Pekkolay 6, Zeynep Cantürk 7, Zeliha Hekimsoy 8, Ozen Oz Gül 9 and Refik Tanakol10

Background: Vitamin D deficiency is a common global health problem and remains highly prevalent in Turkiye, where limited food fortification and heterogeneous clinical practices contribute to variability in testing and supplementation strategies. Aims: To provide Turkiye-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 Turkiye 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 Istanbul 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.

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Screening

Older age: adults aged >65 years
High fall/fracture risk: older adults with a history of falls or low-trauma (fragility) fractures.
Insufficient sunlight exposure:
Homebound individuals (e.g., disability-related confinement, immobility)
Residents of nursing homes/long-term care facilities
Individuals working predominantly indoors for prolonged hours (including night-shift workers in offices, hospitals, or factories)
Chronic debilitating conditions associated with reduced mobility or limited outdoor activity
Obesity: BMI > 30 kg/m2
Chronic use of medications that alter vitamin D metabolism (e.g., antiepileptic drugs, systemic glucocorticoids, azole antifungals, antiretroviral therapy)
Malabsorption states (e.g., inflammatory bowel disease, post-bariatric surgery, cystic fibrosis, and other chronic malabsorptive disorders)
Chronic autoimmune diseases (e.g., rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis)
Skeletal disorders suggestive of deficiency: osteoporosis, osteomalacia, or chronic skeletal/musculoskeletal pain
Chronic kidney disease (especially advanced stages) and chronic liver disease
Hyperparathyroidism
Granulomatous diseases (e.g., sarcoidosis, tuberculosis, histoplasmosis, and other granuloma-forming disorders)
We do not recommend routine community (population-wide) screening for vitamin D deficiency.
Serum 25-hydroxyvitamin D [25(OH)D] should be measured in individuals at increased risk of vitamin D deficiency.
In severe deficiency: In adults with 25(OH)D <12 ng/mL, measurement of serum total calcium (Ca), phosphate (P), parathyroid hormone (PTH), and alkaline phosphatase (ALP) is recommended to assess for secondary hyperparathyroidism and osteomalacia.
In adults with 25(OH)D of 12-20 ng/mL and clinical features potentially attributable to vitamin D deficiency, measurement of Ca, P, iPTH, and ALP is recommended to evaluate for secondary hyperparathyroidism and osteomalacia.
Symptoms suggestive of vitamin D deficiency include unexplained musculoskeletal or bone pain, proximal muscle weakness, muscle cramps, gait or balance impairment, and low-trauma (fragility) fractures.
Prevention—general adult intake: The recommended dietary allowance (RDA) for vitamin D to support bone and muscle health in adults is 600 IU/day. Where dietary intake is inadequate (e.g., limited availability of vitamin D-fortified foods), supplementation of 600 IU/day may be considered.
Prevention—older adults: Because cutaneous synthesis and intestinal absorption decline with age, 800 IU/day of vitamin D supplementation is recommended in older adults to support prevention of deficiency.

Old population aged >75 years:

Empiric vitamin D supplementation is recommended in adults aged >75 years, given evidence suggesting potential benefits on clinically relevant outcomes (including mortality).
In this age group, in settings where vitamin D-fortified foods are limited, an additional 2000 IU/day of Vitamin D is recommended in addition to the dietary intake target (approximately 800 IU/day).
In addition to the estimated dietary requirement (about 800 IU/day, where achievable), empiric supplementation with 2000 IU/day should primarily be considered for selected high-risk groups, particularly in settings where routine screening or food fortification is limited.

Pregnancy

Routine vitamin D screening is not recommended in pregnant women. ,br>(Vitamin D Life - they all need supplementation)
Targeted/selective vitamin D screening may be considered for pregnant women with specific risk factors.
Measurement of serum 25(OH)D should be considered only in pregnant women with >1 established risk factor for vitamin D deficiency.
Given the potential to reduce the risk of adverse pregnancy outcomes (including preeclampsia, stillbirth, preterm birth, small-for-gestational-age birth, and neonatal mortality), empiric vitamin D supplementation is recommended during pregnancy.
During pregnancy, empiric vitamin D supplementation of 2000-2500 IU/day is recommended in addition to dietary intake.
Because most available clinical studies have evaluated daily dosing, a daily regimen is preferred.
During lactation, a vitamin D intake of 2000 IU/day should be ensured.

<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.

Rapid correction (loading)

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.

Modes of administration

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.

Follow-up and monitoring

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.

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Guidelines

Optimum

50,000 IU of Vitamin D once every 2 weeks