Vitamin D Normal Levels by Age
There is no universally agreed-upon age-specific threshold for vitamin D levels; however, most authorities define vitamin D sufficiency as serum 25(OH)D ≥20 ng/mL (50 nmol/L) for bone health across all ages, though some experts recommend targeting ≥30 ng/mL (75 nmol/L) for optimal health outcomes.
Defining Vitamin D Status (All Ages)
The classification of vitamin D status does not vary significantly by age, though the clinical implications and supplementation strategies differ:
Standard Thresholds
- Deficiency: <20 ng/mL (<50 nmol/L) 1, 2
- Insufficiency: 20-30 ng/mL (50-75 nmol/L) 2, 3, 4
- Sufficiency: ≥20 ng/mL (≥50 nmol/L) for bone health 1, 3
- Optimal range: 30-80 ng/mL (75-200 nmol/L) according to some authorities 1, 5
Important Caveat on Age-Related Differences
The actual serum 25(OH)D levels do not have different "normal ranges" by age—rather, the clinical significance and supplementation requirements vary. The Institute of Medicine concluded that 25(OH)D of 20 ng/mL or more covers the requirements of 97.5% of the population regardless of age 3. However, older adults (≥65 years) show increased risk for fractures and falls at lower vitamin D levels, making adequate status more critical in this population 1.
Population-Specific Considerations
Racial and Ethnic Variations
While not age-related, it's crucial to understand that vitamin D levels vary significantly by race, though the clinical implications remain unclear:
- White adults (≥20 years): Mean 25(OH)D levels 57.5-64 nmol/L (23.0-25.6 ng/mL) 1
- African Americans: Mean 32.5-36.25 nmol/L (13.0-14.5 ng/mL) 1
- Hispanics: Mean 44.5-46.5 nmol/L (17.8-18.6 ng/mL) 1
Critical pitfall: Despite lower total serum 25(OH)D levels in African Americans, they do not show the same increased risk for fractures and cardiovascular disease seen in white populations 1. This may be because bioavailable 25(OH)D (accounting for vitamin D-binding protein) is similar between populations 1.
Age-Specific Supplementation Recommendations
While "normal levels" don't change by age, supplementation needs do:
Infants (0-12 months)
- Maintenance dose: 400 IU/day 6, 7, 3, 4
- Preterm infants: 200-1000 IU/day (or 80-400 IU/kg/day) 6
- Upper safety limit: 1,000-1,500 IU/day depending on age 6
Children and Adolescents (1-18 years)
- Maintenance dose: 600 IU/day 6, 3, 4
- Upper safety limits by age: 2,500 IU/day (1-3 years), 3,000 IU/day (4-8 years), 4,000 IU/day (9-18 years) 6
Adults (19-70 years)
- Maintenance dose: 600 IU/day (Institute of Medicine) 3
- Alternative recommendation: 1,500-2,000 IU/day to maintain levels >30 ng/mL (Endocrine Society) 3
Older Adults (≥65 years)
- Maintenance dose: 800 IU/day or 100,000 IU every 3 months 1
- Strong recommendation: All older adults should take a daily 15 μg (600 IU) vitamin D supplement year-round 1
Safety Upper Limits
The safety threshold of 100 ng/mL (250 nmol/L) applies across all ages, though toxicity is rare below this level 1. Hypercalcemia from excess vitamin D has only been observed with daily intake >100,000 IU or serum levels >100 ng/mL in healthy adults 1. For children, serum concentrations >375 nmol/L (150 ng/mL) are associated with acute hypercalcemia and hyperphosphatemia 6.
Clinical Approach to Interpretation
When to Measure 25(OH)D
- Routine screening not recommended for asymptomatic, community-dwelling adults 1
- Measure in high-risk groups: Dark-skinned individuals, institutionalized persons, those with malabsorption, older adults with fracture risk 1
- Measure in children with: Risk factors for deficiency, chronic kidney disease, malabsorption disorders 6
Treatment Targets
- Minimum goal: ≥20 ng/mL (50 nmol/L) for all ages 6, 2, 3
- Optimal goal: 30-44 ng/mL (75-110 nmol/L) according to some experts, though evidence for additional benefit above 30 ng/mL is lacking 1
Key pitfall to avoid: Do not target levels >50 ng/mL routinely, as there is no evidence of additional benefit and it increases risk of oversupplementation 1.