What Does Vitamin D Mean?
Vitamin D is essential for bone health, immune function, and mood. Deficiency is extremely common — especially in winter months or in people with indoor lifestyles.
What Vitamin D Measures
The 25-hydroxyvitamin D test (25-OH D) measures the main circulating form of vitamin D in your blood. It reflects both dietary intake and the vitamin D your skin produces from sunlight. It's the best indicator of overall vitamin D status.
Normal Ranges
Severe deficiency< 12 ng/mL
Deficiency12–19 ng/mL
Insufficient20–29 ng/mL
Optimal30–80 ng/mL
Potentially too high> 100 ng/mL
Reference ranges may vary slightly by lab. Always use the range provided on your specific test report.
What Affects Your Vitamin D Level
- Limited sunlight exposure (indoor lifestyle, winter, high latitudes)
- Darker skin (melanin reduces vitamin D synthesis)
- Age (elderly produce less from sun)
- Obesity (vitamin D gets stored in fat, reducing availability)
- Poor absorption (celiac, Crohn's, gastric bypass)