25-Hydroxyvitamin D2 (Ergocalciferol)
Other marker
Vitamin D2
25-Hydroxyvitamin D2 (Ergocalciferol)
The plant and fungal form of vitamin D, measured as its 25-hydroxy metabolite. Reported separately from D3 when a laboratory uses mass spectrometry, and summed with D3 to give total vitamin D.
PED Notes
Essentially undetectable unless you are supplementing with ergocalciferol or taking a prescription high-dose D2 preparation. Most over-the-counter vitamin D in Australia is D3, so a measurable D2 usually means a specific prescription product. D3 raises total 25(OH)D more effectively than D2, particularly when given as a bolus, so anyone relying on D2 to correct a deficiency is likely under-dosing themselves. Interpret this value only as a component of total vitamin D, never on its own.
How to read this result:
- Undetectable or very low D2 is the normal, expected finding in anyone not taking ergocalciferol. It is not a deficiency.
- What matters clinically is total 25(OH)D (D2 plus D3). Assess sufficiency against that total, not against this fraction.
- If you are supplementing and D2 is the only fraction present, consider switching to D3. Meta-analysis of randomised trials shows D3 raises serum 25(OH)D more effectively than D2, with the advantage clearest for bolus dosing.
If total vitamin D is low:
- Cholecalciferol (D3) -- 1000-4000 IU/day is the standard maintenance range; higher short-term loading doses are a physician decision
- Take with a fat-containing meal -- absorption is substantially better than on an empty stomach
- Vitamin K2 (MK-7) -- 100-200mcg/day is commonly paired with D3 to direct calcium to bone rather than vasculature
- Recheck total 25(OH)D after 8-12 weeks, not sooner; the pool turns over slowly
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