What is the recommended dose of Vitamin D (Vit D) for adults?

Vitamin D Dosing for Adults

For general adult supplementation, take 600-800 IU daily if under 70 years old, or 800 IU daily if 70 or older; for documented deficiency (25(OH)D <20 ng/mL), use 50,000 IU weekly for 8-12 weeks followed by maintenance of 800-2,000 IU daily. 1, 2

Standard Daily Dosing by Age and Risk Status

Healthy Adults (Maintenance)

• Ages 19-70 years: 600 IU daily meets the needs of 97.5% of the population 1, 2
• Ages 71+ years: 800 IU daily to account for decreased skin synthesis with aging 1, 2
• These doses are sufficient when vitamin D status is normal (≥30 ng/mL) 2

At-Risk Populations (Higher Maintenance Doses)

For individuals with risk factors, use 1,500-4,000 IU daily without requiring baseline testing 1, 2. Risk factors include:

• Dark skin pigmentation or veiled individuals with limited sun exposure 1, 2
• Institutionalized or elderly individuals 1, 2
• Obesity (vitamin D sequestration in adipose tissue) 1, 2
• Malabsorption syndromes 1, 2
• Chronic kidney disease stages 3-4 1, 2

Treatment of Documented Deficiency

Loading Phase (25(OH)D <20 ng/mL)

Standard regimen: 50,000 IU of vitamin D3 (cholecalciferol) once weekly for 8-12 weeks 1. This is the cornerstone treatment approach endorsed across multiple guideline societies.

For severe deficiency (<10 ng/mL) with symptoms or high fracture risk:

• 50,000 IU weekly for 12 weeks, then transition to monthly maintenance 1
• Alternative rapid correction: 6,000 IU daily for 4-12 weeks, then maintenance 3

Vitamin D3 is strongly preferred over D2 (ergocalciferol) because it maintains serum levels longer and has superior bioavailability, particularly for intermittent dosing 1, 2

Maintenance Phase After Correction

After completing the loading phase, transition to 800-2,000 IU daily 1, 2. The Endocrine Society specifically recommends at least 2,000 IU daily for optimal health benefits 1.

Alternative monthly dosing: 50,000 IU monthly (equivalent to approximately 1,600 IU daily) can sustain optimal levels 1, 2

Target Serum Levels

The optimal target range is 30-50 ng/mL (75-125 nmol/L) 1, 2, 3. This threshold provides:

• Anti-fall efficacy starting at 24 ng/mL 1
• Anti-fracture efficacy starting at 30 ng/mL 1
• Upper safety limit: 100 ng/mL 1, 2, 4

Monitoring Protocol

Recheck 25(OH)D levels 3 months after initiating supplementation 1, 2, 3. This allows sufficient time for levels to plateau and accurately reflect treatment response.

• For daily dosing: measure after at least 3 months 1, 2
• For intermittent dosing (weekly/monthly): measure just prior to the next scheduled dose 1
• If levels remain <30 ng/mL despite compliance, increase the maintenance dose by 1,000-2,000 IU daily 1

Special Populations Requiring Modified Approaches

Malabsorption Syndromes

For patients with documented malabsorption (post-bariatric surgery, inflammatory bowel disease, celiac disease, pancreatic insufficiency), intramuscular vitamin D3 50,000 IU is the preferred route 1. IM administration results in significantly higher 25(OH)D levels and lower rates of persistent deficiency compared to oral supplementation 1.

When IM is unavailable or contraindicated:

• Use substantially higher oral doses: 4,000-5,000 IU daily for 2 months 1
• Post-bariatric surgery patients specifically need at least 2,000 IU daily maintenance 1

Chronic Kidney Disease (GFR 20-60 mL/min/1.73m²)

Use standard nutritional vitamin D (cholecalciferol or ergocalciferol), NOT active vitamin D analogs 1, 2. CKD patients are at particularly high risk due to reduced sun exposure, dietary restrictions, and urinary losses 1.

Do not use calcitriol, alfacalcidol, doxercalciferol, or paricalcitol for nutritional vitamin D deficiency—these are reserved for advanced CKD with impaired 1α-hydroxylase activity 1, 2

Practical Dosing Rules

Rule of thumb: 1,000 IU daily increases serum 25(OH)D by approximately 10 ng/mL, though individual responses vary due to genetic differences in vitamin D metabolism 1, 2, 4

Daily dosing is physiologically preferable to large intermittent doses 2. Monthly dosing (50,000 IU) has similar effects on 25(OH)D concentration as the equivalent daily dose, but weekly dosing is more effective than single large annual doses 1, 2

Safety Considerations

Daily doses up to 4,000 IU are generally safe for adults 1, 2, 4. Some evidence supports up to 10,000 IU daily for several months without adverse effects 1, 2.

Toxicity typically occurs only when:

• Daily intake exceeds 100,000 IU 1, 2, 4
• Serum 25(OH)D levels exceed 100 ng/mL 1, 2, 4
• Symptoms include hypercalcemia, hyperphosphatemia, suppressed PTH, and hypercalciuria 1

Avoid single ultra-high loading doses (>300,000-540,000 IU) as they have been associated with increased falls and fractures in clinical trials 1, 2

Critical Pitfalls to Avoid

• Do not screen the general population—testing is only appropriate for high-risk individuals 2
• Do not use sun exposure for deficiency prevention due to increased skin cancer risk 1, 2
• Ensure adequate calcium intake (1,000-1,500 mg daily) alongside vitamin D supplementation, as vitamin D enhances calcium absorption and adequate dietary calcium is necessary for clinical response 1
• Do not assume all ethnic groups have the same requirements—darker-skinned individuals need substantially higher doses 2
• For obese patients, recognize that higher doses may be required (potentially 2-4 times higher) to achieve adequate levels due to sequestration in adipose tissue 1, 2