Vitamin D test (25-hydroxy vitamin D)
The 25-hydroxy vitamin D test shows how much vitamin D your body has on hand.
Included in every $199 drawKey benefits of vitamin D testing
- Finds deficiency, which is common and often silent.
- Explains low mood, fatigue, muscle aches or frequent colds.
- Guides supplement dose, so you don't under- or overdo it.
- Supports bone health, especially with age.
- Tracks whether your supplement is working.
What is vitamin D?
Vitamin D is made in your skin from sunlight and absorbed from food and supplements. Your liver turns it into 25-hydroxy vitamin D, the form labs measure.
Why vitamin D matters
Vitamin D helps you absorb calcium for strong bones. It also supports immune function, muscle strength and mood. Low levels are linked to bone loss, falls and more frequent infections.
What your vitamin D results mean
- Below 20 ng/mL: deficient. Supplements are usually needed.
- 20 to 29 ng/mL: insufficient. Many people benefit from raising it.
- 30 to 100 ng/mL: sufficient for most people.
- Above 100 ng/mL: too high, usually from high-dose supplements. It can raise calcium.
- Context matters: darker skin, less sun, winter months, higher body weight and gut conditions all lower vitamin D.
Standard vs. optimal range
| Range | |
|---|---|
| Standard lab range | 30 to 100 ng/mL |
| Insyght optimal range | Set by the Insyght medical team |
Do I need a vitamin D test?
Spend most days indoors, live somewhere with dark winters, or feel low and achy? Vitamin D is one of the most common deficiencies, and one of the easiest to fix once you know.
Stop guessing your supplement dose
Insyght tests vitamin D with iron, ferritin and calcium, then a physician helps you set the right dose. $199 a year.
Similar biomarkers
Frequently asked questions
How much vitamin D should I take?
How long does it take to raise vitamin D?
Should I take vitamin D with K2?
Medically reviewed by Dr. Stephen J. Nicholas, MD, Sports medicine and orthopedic surgery, NY Orthopedics. Last updated September 28, 2026.
