Vitamin D
Also known as 25-Hydroxyvitamin D, 25-OH Vitamin D
What it is
25-hydroxyvitamin D is the storage form of vitamin D circulating in your blood and the standard marker used to assess vitamin D status.
Why it matters
Vitamin D deficiency is common, particularly in people with limited sun exposure, darker skin, or higher body fat, and it doesn't reliably announce itself with obvious symptoms. Beyond its well-known role in calcium absorption and bone health, vitamin D receptors are present throughout the immune system, which is why deficiency has been studied in connection with immune function. It's also one of the more directly actionable results on a panel: unlike genetically fixed markers, a low result typically responds to a dosage adjustment sized to how deficient the result actually is.
Vitamin D is one of the markers in Zaro's Surface panel and every tier above it.
This information is for educational purposes and is not a substitute for professional medical advice. Always talk to a physician about your specific results and health history.
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