Vitamin D Recommended Dietary Allowance (RDA)
The RDA for vitamin D is 600 IU (15 μg) daily for adults aged 19-70 years and 800 IU (20 μg) daily for adults over 70 years, which meets the needs of 97.5% of the population according to the Institute of Medicine. 1, 2
Standard RDA by Age Group
- Adults aged 19-70 years: 600 IU (15 μg) daily is the established RDA 1, 2, 3
- Adults over 70 years: 800 IU (20 μg) daily is recommended due to decreased skin synthesis with aging 1, 2, 3
- Infants under 1 year: 400 IU (10 μg) daily 3, 4
- Children 1 year and older: 600 IU (15 μg) daily 3
These recommendations are based on maintaining serum 25-hydroxyvitamin D [25(OH)D] levels of at least 20 ng/mL (50 nmol/L), which the Institute of Medicine determined covers the requirements of 97.5% of the population 3, 4. However, this represents the minimum to prevent deficiency, not necessarily the optimal level for all health outcomes.
Higher Doses for At-Risk Populations
For individuals at risk of vitamin D deficiency, substantially higher daily doses of 1,500-4,000 IU are recommended rather than the standard RDA. 1, 2
At-risk groups requiring higher supplementation include:
- Dark-skinned or veiled individuals with limited sun exposure: 800 IU daily minimum, often 1,500-2,000 IU 5, 2
- Institutionalized or elderly individuals: 800-1,000 IU daily 5, 2
- Patients with obesity: Higher doses (1,500-4,000 IU) due to sequestration in adipose tissue 1, 2
- Patients with malabsorption syndromes (inflammatory bowel disease, celiac disease, post-bariatric surgery): 2,000-5,000 IU daily or higher 1, 3
- Chronic kidney disease stages 3-4: 1,500-4,000 IU daily 1, 2
Important Distinction: RDA vs. Optimal Dosing
The Endocrine Society guidelines differ from the Institute of Medicine, recommending higher intakes to achieve serum 25(OH)D levels of at least 30 ng/mL rather than 20 ng/mL 1, 3. This reflects different goals:
- Institute of Medicine RDA (600-800 IU): Prevents deficiency in 97.5% of the population, targeting 25(OH)D ≥20 ng/mL 3, 4
- Endocrine Society recommendations (1,500-2,000 IU for adults): Achieves optimal levels of 30 ng/mL for broader health benefits including fracture prevention 1, 3
The discrepancy exists because the Institute of Medicine focused narrowly on bone health, while other organizations consider additional health outcomes where higher vitamin D levels may be beneficial 3, 6.
Dietary Sources vs. Supplementation Reality
Vitamin D occurs naturally in very few foods, making supplementation essential for most people to meet even the basic RDA. 7
Natural food sources include:
- Fatty fish (salmon, sardines): 5-25 μg per 100g 7
- Egg yolks: 1.3-2.9 μg per 100g 7
- Fortified foods (breakfast cereals, milk, orange juice): Variable amounts 5, 7
A cup of fortified milk provides approximately 100 IU, meaning you would need 6-8 cups daily to meet the RDA through diet alone 2. This is why older adults living independently are specifically advised to take a daily 15 μg (600 IU) vitamin D supplement all year round in addition to dietary intake 5.
Safety Parameters
- Daily doses up to 4,000 IU are generally safe for adults and considered the tolerable upper intake level 1, 2, 6
- Some evidence supports up to 10,000 IU daily for several months without adverse effects in specific circumstances 1, 2
- Toxicity typically occurs only with prolonged daily doses exceeding 100,000 IU or serum levels >100 ng/mL 1, 2
Critical Pitfall to Avoid
Do not assume the RDA of 600-800 IU is sufficient for everyone. The RDA represents the minimum to prevent deficiency in the general population with some sun exposure 3, 4. Individuals with limited sun exposure, dark skin, obesity, malabsorption, or chronic disease require substantially higher doses (1,500-4,000 IU daily) to achieve adequate vitamin D status 1, 2. Additionally, relying solely on dietary sources without supplementation is insufficient even with optimal food choices 7.