The storage form of vitamin D — core nutrient status marker, deficient in ~40% of adults.
25-hydroxyvitamin D (25-OH-D) is the circulating storage form of vitamin D and the standard biomarker of vitamin D status. Values <20 ng/mL indicate deficiency; 20–29 insufficiency; 30+ is the standard sufficiency threshold. Optimization-focused practitioners typically target 50–80 ng/mL based on observational data linking higher levels with reduced CVD, cancer, and all-cause mortality.
Vitamin D is fat-soluble and status is driven primarily by sunlight exposure, dietary intake (fatty fish, fortified dairy), and supplementation. Deficiency is shockingly common — 30–50% of adults in temperate latitudes, higher in people with darker skin or limited sun exposure.
Vitamin D status is influenced by: sun exposure (UVB), latitude + season, skin pigmentation (darker skin requires more sun), age (older skin makes less D per exposure), body fat (fat-soluble — high adiposity sequesters D), kidney function, and supplementation. Most people need 2000–5000 IU/day oral D3 + K2 to hit 50+ ng/mL.
Track at baseline on every protocol — D status affects testosterone, immune function, and bone health independent of any peptide. Re-test 8–12 weeks after starting supplementation to ensure dose is adequate. Pair with calcium, phosphorus, and PTH if values are extreme.
Upload any lab PDF and MyProtocolStack maps your values to Vitamin D and 40+ other biomarkers. StackAI interprets the trend in context of your protocol.
Start tracking →Informational only — not medical advice. Reference ranges vary by lab and individual context. Work with a licensed provider to interpret your specific results.