Nutritional

25-OH Vitamin D

Clinical biomarkerVitamin statusBloodnmol/L

The standard circulating marker used to assess vitamin D status.

What it measures

Serum 25-hydroxyvitamin D.

Why it matters

Used clinically to evaluate vitamin D status in appropriate contexts.

How to interpret it

Interpret using clinical guidance and individual risk factors.

Important limitations

Association with outcomes does not mean higher concentrations are always better; supplementation effects depend on population and baseline status.

Evidence status

Clinical biomarker

Established nutritional biomarker; not a direct biomarker of aging.

Research & guidance

Original papers, validation studies, reviews and clinical guidance connected to this measurement.

clinical guideline

Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline

Journal of Clinical Endocrinology & Metabolism · 2024

The guideline cautions that associations between 25(OH)D and many diseases do not establish causality and questions routine testing for disease prevention in people without indications.

For education and evidence exploration, not diagnosis or individualized medical advice.