Normal Vitamin D Levels
Normal vitamin D levels are defined as serum 25-hydroxyvitamin D [25(OH)D] of at least 30 ng/mL (75 nmol/L) for optimal health benefits, with an upper safety limit of 100 ng/mL. 1, 2
Defining Vitamin D Status
The classification of vitamin D status follows these thresholds:
- Deficiency: 25(OH)D levels below 20 ng/mL (50 nmol/L) 1, 3
- Insufficiency: 25(OH)D levels between 20-30 ng/mL (50-75 nmol/L) 1, 2
- Sufficiency/Normal: 25(OH)D levels of 30 ng/mL or higher (≥75 nmol/L) 1, 2, 3
- Optimal range: 30-60 ng/mL (75-150 nmol/L) 4
- Upper safety limit: 100 ng/mL 1, 2
Clinical Significance of Target Levels
The 30 ng/mL threshold is clinically important because anti-fracture efficacy begins at this level, while anti-fall efficacy starts at 24 ng/mL. 1, 2
- Levels below 20 ng/mL are associated with increased risk of secondary hyperparathyroidism, impaired calcium absorption, and bone disease 1, 3
- Levels of 20-30 ng/mL may meet basic skeletal needs but are insufficient for optimal musculoskeletal and potentially extraskeletal health 1, 2
- Levels above 30 ng/mL provide optimal benefits for bone health, fall prevention, and fracture reduction 1, 2, 5
Guideline Perspectives on Normal Levels
There is some variation among professional organizations regarding optimal targets:
- The Endocrine Society defines deficiency as <20 ng/mL and insufficiency as 21-29 ng/mL, recommending treatment for deficiency 1
- The Institute of Medicine concluded that levels of 20 ng/mL meet the needs of nearly all the population for bone health 1
- International expert consensus (Autoimmunity Reviews) recommends a target range of at least 30-40 ng/mL for patients with or at risk for musculoskeletal problems, cardiovascular disease, autoimmune disease, and cancer 1
The weight of evidence from fall and fracture prevention studies supports maintaining levels at or above 30 ng/mL rather than the lower 20 ng/mL threshold. 1, 2, 5
Important Considerations for Interpretation
- Assay selection matters: Use an assay that measures both 25(OH)D2 and 25(OH)D3 for accurate assessment 1, 2
- Seasonal variation: Vitamin D levels are typically lowest after winter months 2
- Inflammation effects: C-reactive protein (CRP) >40 mg/L can significantly reduce plasma vitamin D levels, complicating interpretation 2
- Individual variability: Response to supplementation varies due to genetic differences in vitamin D metabolism, body composition, and environmental factors 1, 2
Common Pitfall to Avoid
Do not confuse 25(OH)D with 1,25-dihydroxyvitamin D [1,25(OH)2D]. Serum 25(OH)D is the correct marker for vitamin D status, while 1,25(OH)2D provides no information about vitamin D status and is often normal or even elevated in vitamin D deficiency due to secondary hyperparathyroidism. 3