Vitamin D
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.
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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
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)
Foods that may help
Fatty fish (salmon, sardines, mackerel)
Richest natural dietary source
Egg yolks
Moderate amount, easy daily option
Fortified milk & plant milks
Added vitamin D for bone health
Mushrooms (UV-exposed)
Only plant source of vitamin D2
Cod liver oil
Traditional high-potency source
When to see your doctor
If your level is below 20 ng/mL, discuss supplementation with your doctor. Vitamin D3 (cholecalciferol) is typically recommended over D2. Most adults benefit from 1000–2000 IU/day, but doses above this should be doctor-supervised.
Related biomarkers
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Educational content only · Not medical advice