The test measures 25-hydroxyvitamin D, the storage form that best reflects your overall status. It is one of the most commonly low results on a blood panel, particularly in northern latitudes and in winter.
Check your value
Reference range used: 30–80 ng/mL. Runs in your browser — nothing is stored.
ng/mL
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Wellness information, not medical advice. Reference ranges vary between laboratories and depend on age, sex and context. This page cannot diagnose anything — always read your result with the range printed on your own report, and discuss concerns with a doctor.
Vitamin D behaves more like a hormone than a vitamin, with receptors across many tissues — which is why deficiency has been studied in connection with so many different outcomes.
Why it matters
Vitamin D status is one of the few widely-tested markers that is both frequently low and straightforward to address. Its clearest established role is in calcium absorption, bone health and muscle function.
What influences your vitamin d (25-oh)
Sun exposure — latitude, season, time outdoors and sunscreen all change synthesis dramatically. Above roughly 37° latitude, winter sun produces almost none.
Skin tone: more melanin means longer exposure is needed for the same synthesis.
Body composition, since vitamin D is fat-soluble and distributes into fat tissue.
Age, as the skin's capacity to synthesise it declines.
What to do with the result
If you are low, sunlight alone is often not enough between autumn and spring at European latitudes.
Vitamin D is fat-soluble — taking it with a meal containing fat improves absorption.
More is not better. Very high intakes can cause harm through calcium overload, so dosing is worth confirming with a doctor rather than guessing.
Divide nmol/L by 2.5 to get ng/mL. So 50 nmol/L is 20 ng/mL. Mixing the two scales is one of the most common misreadings of this test.
How long until levels rise?
Typically 8 to 12 weeks of consistent supplementation before a retest shows a stable change.
Should everyone supplement?
Not automatically. Testing first is more sensible than guessing, and dosing depends on how low you are — a question for a doctor.
See this marker in context
A single value tells you little on its own. PhisBio Lab reads your whole blood panel and shows how five body systems — including Metabolism — are doing together.
Holick MF, et al. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab.
Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D.