Vitamin D 25(OH)(Vit D)

Vitamin D is more hormone than vitamin. Optimal status influences testosterone production, immune regulation, mood, bone density, and skeletal muscle function. The measured 25-hydroxyvitamin D level reflects total body stores and is the appropriate screening test; the active 1,25-dihydroxy form is rarely useful outside specific renal and granulomatous conditions.

Optimal range

50–80ng/mL

Clinical "normal"

30–100 ng/mL

Avg. cost (US)

$45

Test frequency

Annually (twice if dosing aggressively)

When to measure

Any time of day, fasted not required.

How to measure

25-hydroxyvitamin D total — standard immunoassay or LC-MS/MS. The active form (1,25-OH) is rarely needed.

Average cost

≈ $45 cash price. Often covered by insurance with relevant ICD-10.

Why this biomarker matters

Roughly 40 percent of US adults have a 25(OH)D level below 20 ng/mL, the conventional cutoff for deficiency. The Endocrine Society and the Vitamin D Council suggest a target range of 30 to 50 ng/mL for general health, with some longevity-focused clinicians aiming for 40 to 60 ng/mL. Levels above 80 to 100 ng/mL offer no additional benefit and approach the threshold where hypercalcemia and kidney stones become measurable risks. Observational data link low 25(OH)D with elevated all-cause mortality, increased respiratory infection rates, depressed mood, reduced testosterone in men, and accelerated bone loss. Randomized trials of vitamin D supplementation in deficient populations consistently improve bone outcomes and modestly reduce respiratory infection rates; trials in already-replete populations (the VITAL trial and several others) have largely failed to find additional benefit on cardiovascular events or cancer incidence, reinforcing the "correct deficiency, do not chase high-normal" interpretation. Supplementation with 1,000 to 4,000 IU per day of D3 (cholecalciferol) usually restores deficient individuals to the 30 to 50 ng/mL range within 8 to 12 weeks. Patients with malabsorption, obesity (where D distributes into adipose tissue), or persistent deficiency despite reasonable dosing should be evaluated for celiac disease, magnesium deficiency, or CYP enzyme variation.