Vitamin D

Measured in ng/mL

A measure of your body's main circulating form of vitamin D — where the line for 'enough' sits is genuinely debated between expert bodies.

What it is

This test measures 25-hydroxyvitamin D, the storage form that circulates in blood and is considered the best available indicator of your overall vitamin D status. Levels naturally drift with sun exposure and season (often lower in winter), and can be influenced by body composition, skin tone, absorption, and certain medications. Worth knowing honestly: major expert groups disagree about thresholds — the Institute of Medicine (now NAM) and the Endocrine Society have set different cut-points for 'sufficiency' — so the same number can be labeled differently depending on which framework a lab or clinician uses, which is a good reason to discuss your result in context rather than against a single line.

Typical range

  • Adults20–100 ng/mL

Source · IOM/NAM (2011)

Reference ranges vary between laboratories, and what is normal for you depends on your own history. Your own lab’s range is the one printed on your report.

Worth asking your clinician

  • Which threshold or guideline is my lab using, and how would my result be read under a different one?
  • Does the season, my sun exposure, or anything in my health history change how you'd interpret this number for me?
  • Is this a result you'd want to look at again at a different time of year?