What is the recommended dose of vitamin D (International Units) for adults?

Vitamin D Dosage for Adults

For general adult supplementation, 800-1,000 IU daily is recommended for those with inadequate sun exposure, while adults with documented vitamin D deficiency require an initial loading dose of 50,000 IU weekly for 8-12 weeks followed by maintenance therapy of 800-2,000 IU daily. 1

Standard Maintenance Dosing by Age and Risk

Healthy Adults (19-70 years):

• 600-800 IU daily meets the needs of 97.5% of the population 2, 3
• This baseline assumes adequate sun exposure and dietary intake 3

Older Adults (≥70 years):

• 800 IU daily minimum is recommended due to decreased skin synthesis with aging 1, 2, 3
• Higher doses of 700-1,000 IU daily provide superior anti-fall and anti-fracture effects 1

High-Risk Populations Requiring Higher Doses:

• Dark-skinned or veiled individuals with limited sun exposure: 800 IU daily without baseline testing 4, 1
• Institutionalized individuals: 800 IU daily without baseline testing 4, 1
• Patients at risk for deficiency (obesity, malabsorption, chronic illness): 1,500-4,000 IU daily 2

Treatment Protocol for Documented Deficiency

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

• 50,000 IU of vitamin D3 (cholecalciferol) once weekly for 8-12 weeks 1
• Vitamin D3 is strongly preferred over D2 (ergocalciferol) as it maintains serum levels longer and has superior bioavailability 1
• This cumulative dose of 400,000-600,000 IU is necessary to replenish vitamin D stores 5

Maintenance Phase (after achieving target levels):

• 800-2,000 IU daily or 50,000 IU monthly (equivalent to approximately 1,600 IU daily) 1
• Target serum 25(OH)D level: at least 30 ng/mL for optimal health benefits, particularly for anti-fracture efficacy 4, 1

Special Populations Requiring Modified Dosing

Malabsorption Syndromes (inflammatory bowel disease, post-bariatric surgery):

• Intramuscular vitamin D 50,000 IU is preferred when available, as it results in significantly higher levels than oral supplementation 1
• If IM unavailable: 4,000-5,000 IU daily orally for 2 months, then maintenance of at least 2,000 IU daily 1

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

• Standard nutritional vitamin D replacement with ergocalciferol or cholecalciferol is appropriate 1
• Do NOT use active vitamin D analogs (calcitriol, alfacalcidol) to treat nutritional deficiency 1

Monitoring and Target Levels

When to Check Levels:

• Measure 25(OH)D at least 3 months after starting supplementation to allow plateau to be reached 4, 1
• If using intermittent dosing (weekly or monthly), measure just prior to the next scheduled dose 1

Target Ranges:

• Optimal range: 30-80 ng/mL for health benefits 1, 2
• Upper safety limit: 100 ng/mL 4, 1
• Anti-fall efficacy begins at ≥24 ng/mL; anti-fracture efficacy at ≥30 ng/mL 1

Practical Dosing Rule of Thumb

An intake of 1,000 IU vitamin D daily increases serum 25(OH)D by approximately 10 ng/mL, though individual responses vary due to genetic factors, body composition, and baseline levels. 1, 2

Critical Safety Considerations

Safe Upper Limits:

• Daily doses up to 4,000 IU are generally safe for adults 1, 2
• Some evidence supports up to 10,000 IU daily for several months without adverse effects 1, 2
• Toxicity typically occurs only with daily intake exceeding 100,000 IU or serum levels >100 ng/mL 1

Avoid These Dosing Errors:

• Never use single annual mega-doses (≥300,000-500,000 IU) as they are associated with increased falls and fractures 1, 5
• Do not use active vitamin D analogs for nutritional deficiency 1

Essential Co-Interventions:

• Ensure adequate calcium intake of 1,000-1,500 mg daily from diet plus supplements 1
• Calcium supplements should be taken in divided doses of no more than 600 mg at once for optimal absorption 1

Key Clinical Pearls

• Vitamin D3 (cholecalciferol) is preferred over D2 (ergocalciferol), especially for intermittent dosing regimens 1
• Daily dosing is physiologically preferable, but weekly or monthly regimens are acceptable alternatives for compliance 1, 2
• Individual response varies significantly due to genetic polymorphisms in vitamin D metabolism, body fat (which sequesters vitamin D), and muscle mass 1, 2
• Supplementation benefits are primarily seen in those with documented deficiency, not in the general population with normal levels 1