Biomarker
Vitamin D
Also known as 25-hydroxy Vitamin D · 25(OH)D
A fat-soluble vitamin that functions more like a hormone — widely deficient, with broad effects on immune, bone and metabolic health.
Definition
Vitamin D is measured as serum 25-hydroxyvitamin D, the storage form. Values under 30 ng/mL are insufficient; under 20 are deficient. Beyond bone health, adequate vitamin D is associated with immune function, mood, and insulin sensitivity. Supplementation at 2000–5000 IU daily corrects most cases; high-dose loading is reserved for severe deficiency.
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