Vitamin D (25-Hydroxyvitamin D)
The sunshine hormone behind bone strength, immune function, and mood — and one of the most common deficiencies worldwide.
Track This Free → ← All BiomarkersWhat Is Vitamin D?
Vitamin D is a fat-soluble hormone your skin produces from sunlight and that you also get from food and supplements, and blood tests measure its storage form, 25-hydroxyvitamin D (25-OH-D), in nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L).
Beyond its classic role in absorbing calcium for bone health, vitamin D influences immune function, muscle strength, and mood regulation. Because most people get it from sun exposure that varies by season, latitude, skin tone, and time spent indoors, deficiency is extremely common — and often silent until it shows up as fatigue, frequent illness, bone pain, or low mood.
Vitamin D Normal Range and Reference Values
| Category | Value | Notes |
|---|---|---|
| Deficient | Below 20 ng/mL | Below 50 nmol/L |
| Insufficient | 20–29 ng/mL | 50–74 nmol/L |
| Sufficient | 30–50 ng/mL | 75–125 nmol/L |
| High / potential toxicity | Above 100 ng/mL | Above 250 nmol/L |
What Causes Vitamin D to Change
The most common drivers behind a change in Vitamin D are:
- Limited sun exposure — indoor lifestyle, winter months, high latitude
- Darker skin, which produces vitamin D more slowly
- Older age, as skin synthesizes less vitamin D over time
- Obesity, which sequesters vitamin D in fat tissue
- Malabsorption conditions such as celiac or Crohn's disease
- Consistent sunscreen use without dietary or supplemental replacement
How Hunuu Tracks Vitamin D
Vitamin D is one of Hunuu's high-HIP-weight lab markers — it moves the score even from a single reading because deficiency is both common and consequential. Log it through the BODY pillar's Add Lab Result form. On the roadmap, Hunuu pairs it with time-in-daylight data from your wearable, connecting the lab value to the daily behavior that most directly changes it.
Frequently Asked Questions
What is a normal vitamin D level?
Most labs consider 30–50 ng/mL (75–125 nmol/L) sufficient. Below 20 ng/mL is deficient, and 20–29 ng/mL is insufficient. Optimal targets vary between guidelines and clinicians.
What are the symptoms of low vitamin D?
Common signs include fatigue, frequent infections, bone or muscle pain, low mood, and hair thinning. Many people with mild deficiency have no obvious symptoms at all, which is why testing matters.
How can I raise my vitamin D level?
Sensible sun exposure, vitamin D-rich foods (fatty fish, fortified dairy, egg yolks), and supplementation guided by a clinician. Because it is fat-soluble, taking it with a meal containing fat improves absorption.
Can you have too much vitamin D?
Yes, though it is rare and almost always from over-supplementation, not sun. Levels above 100 ng/mL can cause dangerously high calcium. Very high-dose supplements should only be taken under medical supervision.
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