Vitamin D Testing
Confirms whether you actually need to supplement, and how much.
What it does
A 25-hydroxyvitamin D test is the only reliable way to know whether supplementation is needed and at what dose. Sun exposure, skin tone, latitude, and season shift baseline enough that dosing without testing means guessing.
Measures serum 25-hydroxyvitamin D, the major circulating form and the standard clinical indicator of vitamin D status.
What the evidence shows
Overall evidence strength: High certainty
Who it's for, who should skip
Anyone supplementing or considering it. Test first, then dose to the 30–50 ng/mL range and retest — fixed high-dose supplementation without testing either wastes money or under-doses a real deficiency.
Running it
Measuring it
Retest Vitamin D — No guideline-based retest interval — the Endocrine Society (2024) recommends against routine follow-up 25(OH)D testing. Retest on a clinician's specific indication, not on a calendar..
Stacking & alternatives
Access & cost
Ordered as a lab test through the bloodwork lane.
Last reviewed 27 August 2026.