Normal Range of Vitamin D
The normal range of vitamin D is 30-80 ng/mL (75-200 nmol/L), with deficiency defined as levels below 20 ng/mL and insufficiency as 20-30 ng/mL. 1, 2, 3
Defining Vitamin D Status
Standard Thresholds
- Deficiency: Serum 25-hydroxyvitamin D [25(OH)D] below 20 ng/mL (50 nmol/L) 4, 1, 3
- Insufficiency: 20-30 ng/mL (50-75 nmol/L) 1, 5, 2
- Optimal/Sufficient: 30-80 ng/mL (75-200 nmol/L) 1, 5, 2, 3
- Upper safety limit: 100 ng/mL (250 nmol/L) 1, 6
- Severe deficiency: Below 10-12 ng/mL, which significantly increases risk for osteomalacia and rickets 1
Important Context on Thresholds
The U.S. Preventive Services Task Force acknowledges there is no consensus on how to define vitamin D deficiency, and different organizations use varying cut points. 4 The Institute of Medicine concluded that 25(OH)D of 20 ng/mL or more covers the requirements of 97.5% of the population for bone health. 4, 7 However, the Endocrine Society and many experts recommend targeting levels above 30 ng/mL for optimal health benefits, particularly for anti-fracture efficacy and fall prevention. 1, 7, 3
Population-Specific Considerations
For the Indian population specifically, guidelines recommend targeting higher levels of 40-60 ng/mL due to darker skin pigmentation and high prevalence of deficiency (65-78% using the 20 ng/mL cutoff). 6 This is higher than the Western target of 30-44 ng/mL. 6
Clinical Significance of Different Levels
Functional Thresholds
- Anti-fall efficacy begins: ≥24 ng/mL 1
- Anti-fracture efficacy begins: ≥30 ng/mL 1
- Increased secondary hyperparathyroidism risk: <15 ng/mL, even in dialysis patients 1
Normal Ranges in Sunny Countries
In populations with adequate sun exposure, normal vitamin D levels typically range from 54-90 ng/mL, demonstrating that higher levels are physiologically normal. 2
Key Measurement Considerations
Measure total 25-hydroxyvitamin D (both D2 and D3 combined), as this is the barometer for vitamin D status. 3 Serum 1,25-dihydroxyvitamin D [1,25(OH)₂D] should not be used to assess vitamin D status, as it provides no information about stores and is often normal or even elevated due to secondary hyperparathyroidism in deficiency states. 3
Common Pitfalls
- Assay variability: Until recently, lack of a reference standard for vitamin D testing complicated accurate measurement, making prevalence estimates difficult to determine. 4
- Population differences: African Americans have paradoxically lower fracture rates despite lower 25(OH)D levels compared to white persons, possibly due to differences in vitamin D-binding protein and bioavailable vitamin D. 4
- Inflammation effects: C-reactive protein (CRP) >40 mg/L can significantly reduce plasma vitamin D levels, complicating interpretation. 1
- Seasonal variation: Vitamin D levels are typically lowest after winter, which should be considered when interpreting results. 1