Vitamin D Dosage for Adults
For general adult supplementation, take 600-800 IU daily if you're under 70 years old, and 800 IU daily if you're 70 or older, which meets the needs of 97.5% of the population according to the Institute of Medicine. 1
Standard Daily Dosing by Age
- Adults aged 18-70 years: 600 IU daily is sufficient to maintain adequate vitamin D status in most individuals 1
- Adults over 70 years: 800 IU daily is recommended to account for decreased skin synthesis with aging 1
- Elderly institutionalized patients: 800 IU daily without baseline testing is appropriate 2
Higher Dosing for At-Risk Populations
If you have risk factors for vitamin D deficiency—including dark skin, limited sun exposure, obesity, malabsorption, or chronic glucocorticoid use—you need substantially higher doses of 1,500-2,000 IU daily for maintenance. 1, 2, 3
- Dark-skinned or veiled individuals: 800-2,000 IU daily without baseline testing 2, 4
- Obese patients (BMI >30): At least 2,000 IU daily, potentially up to 4,000 IU daily 4, 5
- Patients on chronic glucocorticoids (≥2.5 mg/day for >3 months): 600-800 IU daily minimum, with target serum 25(OH)D levels of 30-50 ng/mL 1
- Post-bariatric surgery patients: 2,000-3,000 IU daily due to malabsorption 2, 6
Target Serum Levels
The optimal target range for serum 25-hydroxyvitamin D is 30-50 ng/mL for most health benefits, with 100 ng/mL serving as the upper safety limit. 1, 2, 7
- Levels below 20 ng/mL indicate deficiency requiring treatment 6, 4
- Levels between 20-30 ng/mL represent insufficiency 6, 4
- Anti-fracture efficacy begins at levels ≥30 ng/mL 6
Practical Dosing Considerations
As a rule of thumb, every 1,000 IU of daily vitamin D intake increases serum 25(OH)D by approximately 10 ng/mL, though individual responses vary significantly. 2, 7, 5
- Daily dosing is physiologically preferred, but weekly or monthly regimens are acceptable alternatives 2, 7
- Vitamin D3 (cholecalciferol) is preferred over D2 (ergocalciferol) for better bioavailability and longer-lasting effects 6, 8
- Most international authorities consider 2,000 IU daily as absolutely safe for long-term use 2, 7
Safety Parameters
Daily doses up to 4,000 IU are generally considered safe for adults, with some evidence supporting up to 10,000 IU daily for several months without adverse effects. 2, 6, 9
- Toxicity is rare and typically occurs only with daily intake exceeding 100,000 IU or serum levels above 100 ng/mL 2, 7
- Single mega-doses (>300,000 IU) should be avoided as they may be inefficient or harmful 6, 9
Monitoring Recommendations
Wait at least 3 months after starting supplementation before measuring 25(OH)D levels to allow serum concentrations to plateau. 2, 6, 7
- Consider seasonal variation when interpreting results, with lowest levels typically occurring after winter 1, 7
- For patients on intermittent dosing (weekly/monthly), measure levels just before the next scheduled dose 6
Common Pitfalls to Avoid
The most common mistake is using the standard 600-800 IU daily dose for patients with malabsorption, obesity, or chronic glucocorticoid use—these populations require 2-4 times higher doses to achieve adequate levels. 1, 2, 4, 5
- Don't assume the Institute of Medicine's recommendations apply to all ethnic groups—darker-skinned individuals need substantially higher doses 1, 4
- Don't forget to ensure adequate calcium intake (1,000-1,200 mg daily) alongside vitamin D supplementation 1, 6
- Avoid prescribing active vitamin D analogs (calcitriol, alfacalcidol) for nutritional vitamin D deficiency—use cholecalciferol or ergocalciferol instead 6
Special Clinical Contexts
For patients with documented deficiency (25(OH)D <20 ng/mL), standard daily doses are inadequate—a loading dose regimen of 50,000 IU weekly for 8-12 weeks is required, followed by maintenance dosing of at least 2,000 IU daily. 6, 3, 9