Vitamin D 25-Hydroxy Vitamin D
A vitamin your skin makes from sunlight, and food tops up.
Also printed asVitamin D (25-Hydroxyvitamin D) · 25-OH Vitamin D · 25(OH)D · Calcidiol · Vitamin D 25-Hydroxy · Total Vitamin D
What it measures
A hormone your skin makes from sunlight, measured in its storage form.
Controls how much calcium you absorb from food, so a shortfall pulls calcium out of bone; it also affects immunity and mood.
Why it matters for how long you stay well
It is what lets your gut take calcium from food, so years of running low quietly costs bone strength, and bone strength in your fifties decides how independent you are in your eighties.
How it shows up in daily life
Running low can show up as aching bones, sore muscles, low mood, and picking up every cold that goes around.
High and low readings
When it reads high
Almost always from supplements; a very high level needs a physician.
When it reads low
Most Indians are low - indoor work, sunscreen and darker skin all reduce what the skin makes. It is one of the easiest things to fix.
What moves it
Daily life
- time outdoors in the middle of the day
- how much skin is uncovered
- darker skin, which needs longer sun for the same amount
- sunscreen and staying indoors
- body weight, since it hides in fat
Medicines known to shift it
- vitamin D supplements (raise it)
- steroids (lower it)
Listed so a result can be read in context. It is not advice to start, stop or change any medicine; that decision belongs with your physician.
Read it with
Markers that move this one, or that this one moves. One number read alone can mislead.
- CalciumKnown mechanism
As this rises, Calcium rises with it
Vitamin D is what lets your gut take calcium out of food. Without enough of it, calcium can be on your plate and still never get in.
- PhosphorusKnown mechanism
As this rises, Phosphorus rises with it
Vitamin D raises the absorption of phosphorus alongside calcium. So the two minerals tend to move together whenever vitamin D changes.
Common questions
What does 25-Hydroxy Vitamin D measure?
A hormone your skin makes from sunlight, measured in its storage form. Controls how much calcium you absorb from food, so a shortfall pulls calcium out of bone; it also affects immunity and mood.
What does a high Vitamin D result usually mean?
Almost always from supplements; a very high level needs a physician.
What does a low Vitamin D result usually mean?
Most Indians are low - indoor work, sunscreen and darker skin all reduce what the skin makes. It is one of the easiest things to fix.
What is the usual reference range for Vitamin D?
A broad adult reference band is 30–100 ng/mL. Labs differ, so read your result against the band printed on your own report.
Educational only, not a diagnosis. A single number means little without your history and the rest of your panel, so discuss your own results with your physician.
Typical adult reference band
- Adults
- 30–100 ng/mL
Labs differ. The band printed on your own report is the one that applies to your result.
Reported in ng/mL, nmol/L
Ageing relevance
4/5
A strong independent predictor of illness and mortality in large cohorts.
Indian reference data
Published data on this marker in Indian adults: Delhi NCR SEAJPH 2023 (urban median 7.7, rural 16.2).
Worth knowing
Your skin makes it from sunlight, which is why it behaves more like a hormone than a vitamin.
Related reading
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