Vitamin D (25-Hydroxy)
25-hydroxy vitamin D is the main circulating form of vitamin D and the best marker of body stores. Adequate levels support bone mineralization, calcium absorption, immune function, and muscle strength. Deficiency is common, especially at northern latitudes and in people with limited sun exposure, and is linked with osteoporosis, falls, and higher infection risk.
Units: ng/mL; some labs report nmol/L (nmol/L = ng/mL × 2.5). Check the units on your report before comparing to any range here.
Optimal range: who says what
Institutions, researchers and practitioners draw the line in different places. Each position is listed with who holds it and, where a document states it, a link. How we verify ranges.
- Institution or study>=20 ng/mL sufficientNASEM (Institute of Medicine) dietary reference intakesSet for bone health in the general population
- Institution or study30-100 ng/mL; deficiency below 20Endocrine Society clinical practice guideline (2011)Written for clinical care of patients at risk of deficiency
- Named practitioner40-60 ng/mLDr. Rhonda Patrick · Maximize Health with Vitamin D3
- Named practitioner50-80 ng/mLLife Extension · Lab Testing Protocol (Suggested Optimal Ranges)Disclosure: Life Extension sells lab panels that appear in our blood-test comparisons.
- Named practitioner50-70 ng/mLTracey O'Shea (Kresser Institute) · The Lipid Panel Was Fine. The Patient Was Not: A Case in Advanced Cardiovascular Risk Assessment
- Lab reference intervalDeficient: <20 ng/mL, Insufficient: 20-29 ng/mL, Sufficient: 30-100 ng/mLWhat a lab report flags against. A lab interval is not an optimal target.
Practitioner targets are individual positions, often tighter than guideline ranges. Each was checked against its article before publishing.
17 of 21 itemized panels
Vitamins & Nutrients
What is Vitamin D (25-Hydroxy)?
Vitamin D (specifically 25-hydroxyvitamin D, or 25(OH)D) is the best marker of your body's vitamin D status. Technically a hormone rather than a vitamin, vitamin D is synthesized in your skin from sun exposure (UVB radiation converts 7-dehydrocholesterol to vitamin D3) and obtained from dietary sources (fatty fish, fortified foods, supplements). It's then converted to 25(OH)D in the liver (storage form, measured in blood tests) and finally to active 1,25-dihydroxyvitamin D in the kidneys.
Vitamin D deficiency is common, especially with limited sun exposure, darker skin, older age, and obesity. In observational studies, low 25(OH)D is linked to fractures, infections, cardiovascular disease, and higher mortality. Randomized trials have mostly not reproduced those links: a review of 290 cohort studies and 172 trials concluded that low 25(OH)D is mainly a marker of ill health (Autier 2014), and the VITAL trial found 2,000 IU/day did not prevent cancer or cardiovascular events. The clearest trial benefits are for fractures at about 800 IU/day in older adults and for respiratory infections in people who start out deficient. Targets above the 30 ng/mL sufficiency threshold differ by source; named positions are listed in the ranges section.
Sun exposure is the most efficient way to produce vitamin D, but latitude, season, time of day, skin pigmentation, sunscreen use, and age all affect synthesis. People living above 35° latitude (north of Atlanta, GA in the US) can't produce vitamin D from sun exposure for 3-6 months in winter. Supplementation is necessary for most people, especially those with dark skin, living in northern latitudes, elderly, or with limited sun exposure.
Why Vitamin D Matters for Longevity
- Bone health: Vitamin D increases calcium absorption in the gut and regulates bone remodeling. Deficiency causes rickets in children and osteomalacia in adults. In pooled trials of people 65 and older, a daily intake of about 800 IU lowered hip fracture risk by 30% (Bischoff-Ferrari 2012).
- Immune function: Vitamin D acts on both innate and adaptive immunity. In a meta-analysis of 25 trials, supplementation reduced acute respiratory infections by about 12% overall (odds ratio 0.88), with most of the benefit in people starting below 10 ng/mL (Martineau 2017).
- Cardiovascular health: Vitamin D receptors are present in the heart and blood vessels, and low levels are associated with hypertension and heart disease in observational studies. In the VITAL trial, 2,000 IU/day did not reduce major cardiovascular events.
- Cancer: Observational studies link higher 25(OH)D with lower risk of some cancers, but in the VITAL trial (25,871 adults, 2,000 IU/day for about 5 years) vitamin D did not lower invasive cancer, including breast, prostate, and colorectal cancer.
- Mood and mental health: Vitamin D receptors are present in the brain, and deficiency is associated with depression in observational studies.
- Metabolic health: Low vitamin D is associated with type 2 diabetes and metabolic syndrome in observational studies.
Interpretation bands (curated, PMID-backed)
Holder: OptimizeBiomarkers editorial synthesis of: Vitamin D: Evidence-Based Health Benefits and Recommendations for Population Guidelines (Grant et al., 2025); Vitamin D deficiency and mortality risk in the general population: a meta-analysis of prospective cohort studies (Zittermann et al., 2012); Meta-analysis of all-cause mortality according to serum 25-hydroxyvitamin D (Garland et al., 2014). No single paper sets these cutoffs; for attributed targets see who says what.
Optimal (Longevity)40-60 ng/mL▼
- Target range used by many longevity-focused practitioners
- The trials reviewed by Autier 2014 and the VITAL trial did not show that raising vitamin D prevents non-skeletal disease
Sufficient (Standard)30-40 ng/mL▼
Meets the standard sufficiency threshold for bone health.
Insufficient20-30 ng/mL▼
- Common range
- Associated with poorer bone health; supplementation is often advised
Deficient<20 ng/mL▼
- Deficiency
- Impairs calcium absorption and bone mineralization
- Associated with fractures, infections and higher mortality in observational studies
What raises or lowers Vitamin D
Causes of high Vitamin D
- Excessive supplementation: >10,000 IU/day chronically for months.
- Primary hyperparathyroidism: Parathyroid tumor causes excess calcium and vitamin D activation.
- Granulomatous diseases: Sarcoidosis, tuberculosis cause unregulated conversion of 25(OH)D to active form, raising blood levels.
- Vitamin D toxicity (rare): Causes hypercalcemia, kidney stones, nausea.
Causes of low Vitamin D
- Insufficient sun exposure: Living >35° latitude, winter months, indoor lifestyle, sunscreen use, clothing coverage.
- Dark skin pigmentation: Melanin blocks UVB absorption. Deficiency is more common in people with darker skin.
- Obesity: Vitamin D sequestered in adipose tissue, lowering blood levels.
- Aging: Older skin makes less vitamin D from the same sun exposure.
- Malabsorption: Celiac disease, Crohn's disease, gastric bypass, pancreatic insufficiency.
- Liver or kidney disease: Impairs conversion of vitamin D to active form.
- Medications: Anticonvulsants, glucocorticoids, cholestyramine, orlistat.
- Dietary insufficiency: Few foods naturally contain vitamin D (fatty fish, egg yolks, fortified milk).
Symptoms when Vitamin D is high or low
When high
- Hypercalcemia: Nausea, vomiting, weakness, frequent urination
- Kidney stones (calcium oxalate)
- Confusion, disorientation
- Constipation
- Cardiac arrhythmias (if severe hypercalcemia)
Toxicity is rare and requires chronic intake >10,000 IU/day for months. Levels >100 ng/mL may cause hypercalcemia.
When low
- Bone pain, muscle weakness, muscle aches
- Frequent infections (colds, flu, respiratory infections)
- Fatigue, tiredness
- Depressed mood, seasonal affective disorder (SAD)
- Bone fractures, low bone density (osteoporosis, osteomalacia)
- Hair loss
- Impaired wound healing
- Cognitive impairment in elderly
Levels below 20 ng/mL are common. In observational studies low levels go with fractures, infections and higher mortality; in trials the clearest benefits are for bone and, in people who start out deficient, respiratory infections.
How to move Vitamin D
Effect sizes (how much something moves the marker) appear only where the paper cited under the item states them. Talk to your clinician before starting or changing any medication or supplement.
Vitamin D Supplementation (Dose Based on Current Level)
- Vitamin D3 (cholecalciferol): Preferred form over D2 (ergocalciferol). More effective at raising 25(OH)D levels.
- Dose depends on your level: The right dose depends on your starting level, body weight and absorption. Repletion doses for deficiency are higher and are best set by a clinician; retest after about 3 months and adjust.
- Take with fat: Vitamin D is fat-soluble; absorption is better when taken with a meal that contains fat.
Sun Exposure (Natural Vitamin D Production)
- UVB exposure: Short periods of midday sun on bare arms and legs a few times a week produce vitamin D in the skin.
- Variables: Latitude (above 35° = minimal winter UVB), season, time of day, skin pigmentation (darker skin needs longer exposure), age (older skin makes less), and sunscreen (blocks most UVB).
- Balance: Sun exposure without burning. Excess UV increases skin cancer risk, while low vitamin D levels are associated with higher mortality in observational studies. Moderate exposure without burning balances the two for most people.
Cofactors for Vitamin D Metabolism
- Vitamin K2 (MK-7): 100-200 mcg/day. Directs calcium to bones (away from arteries). Important when supplementing vitamin D to prevent vascular calcification. Found in natto, fermented foods, cheese.
- Magnesium: 400 mg/day. Required cofactor for vitamin D activation and metabolism. Magnesium deficiency impairs vitamin D metabolism.
- Vitamin A: Vitamin D and A work synergistically. Avoid excessive vitamin A (>10,000 IU) which may antagonize vitamin D.
- Calcium: Ensure adequate intake (1000-1200 mg/day) from diet or supplement if vitamin D is optimized (to support bone mineralization).
Address Malabsorption (if levels don't rise with supplementation)
- Conditions impairing vitamin D absorption: Celiac disease, Crohn's disease, ulcerative colitis, gastric bypass, pancreatic insufficiency.
- Higher doses: People with malabsorption may need higher doses, set and monitored by a clinician.
- Check 25(OH)D after 3 months to confirm absorption.
- Consider intramuscular vitamin D injections if oral supplementation fails.
Correct Underlying Causes of Deficiency
- Obesity: Vitamin D is fat-soluble and sequesters in adipose tissue. People with obesity often need higher doses to reach the same blood level.
- Liver or kidney disease: Impairs conversion to active vitamin D. May need calcitriol (active form) if kidney failure.
- Medications: Anticonvulsants (phenytoin, phenobarbital), glucocorticoids, antiretrovirals increase vitamin D metabolism and lower levels.
When to retest
- Baseline: Check 25(OH)D level before starting supplementation to determine appropriate dose.
- After 3 months of supplementation: Retest to confirm adequate repletion and adjust dose. Targets differ: Rhonda Patrick aims for 40-60 ng/mL, while the Endocrine Society guideline treats 30-100 ng/mL as sufficient (see who says what above).
- Maintenance: Retest annually or every 6 months if optimizing. Levels can drift down if dose insufficient or sun exposure changes seasonally.
- If malabsorption suspected: Retest 3 months after higher-dose supplementation to confirm absorption.
- If treating osteoporosis: Monitor 25(OH)D along with bone markers (CTX, P1NP) and DEXA scan to ensure adequate repletion for bone health.
Scientific Evidence
Vitamin D Status: Cause or Marker?
A systematic review of 290 prospective cohort studies and 172 randomized trials found that low 25(OH)D was linked to many diseases in observational data, but supplementation trials did not reduce disease occurrence. The authors concluded that low 25(OH)D is mainly a marker of ill health. Low-dose supplementation (20 µg, or 800 IU, per day) in older people, mostly women, appeared to reduce all-cause mortality slightly.
Source: Vitamin D status and ill health: a systematic review.
Vitamin D and Respiratory Infections
An individual-participant meta-analysis of 25 trials (10,933 participants) found vitamin D supplementation reduced acute respiratory infections by about 12% overall (odds ratio 0.88). Benefit was limited to daily or weekly dosing, not bolus doses, and was largest in people starting below 25 nmol/L, about 10 ng/mL (odds ratio 0.30).
Vitamin D Dose and Fracture Prevention
Pooled data from 11 trials (31,022 people aged 65 and older) showed a non-significant 10% reduction in hip fracture with assignment to vitamin D. At the highest actual intake (median 800 IU daily), hip fracture risk was 30% lower and non-vertebral fracture risk 14% lower.
Source: A pooled analysis of vitamin D dose requirements for fracture prevention.
VITAL: Vitamin D, Cancer, and Heart Disease
The VITAL trial gave 25,871 US adults 2,000 IU of vitamin D3 daily or placebo for a median 5.3 years. Vitamin D did not lower invasive cancer (hazard ratio 0.96), including breast, prostate, or colorectal cancer, and did not lower major cardiovascular events (hazard ratio 0.97).
Source: Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease.
Which Providers Test Vitamin D (25-Hydroxy)?
Cheapest: Empirical Health at $190/year. Most comprehensive: Function Health, 160+ biomarkers for $365/year.
17 panels that include it, cheapest first
| Provider | Annual Cost | Total Biomarkers | $/Biomarker |
|---|---|---|---|
| $190 | 100+ | $1.90 | |
| $297 | 100+ | $2.97 | |
 Labcorp OnDemand | $338 | 50+ | $6.76 |
 Superpower | $349 | 100+ | $3.49 |
| $349 | 75+ | $4.65 | |
 WHOOP Advanced Labs | $349 | 65 | $5.37 |
 Function Health | $365 | 160+ | $2.28 |
| $365 | 100+ | $3.65 | |
| $449 | 83 | $5.41 | |
| $495 | 80+ | $6.19 | |
| $499 | 100+ | $4.99 | |
| $829 | 54 | $15.35 | |
| $895 | 100+ | $8.95 | |
| $996 | 59 | $16.88 | |
| $1188 | 70+ | $16.97 | |
| $1198 | 40+ | $29.95 | |
| $1950 | 130+ | $15.00 |
$/Biomarker is annual cost divided by the panel's advertised biomarker count, not the price of this one test. We track 23 blood test providers (32 plans); 21 of those plans are itemized marker by marker. Compare all of them.
4 itemized panels do not include Vitamin D (25-Hydroxy)
Marek Health Base · Oura Health Panels · Vitality Blueprint Standard · Vitality Blueprint Elite
11 providers not itemized in our matrix
We have not itemized these marker by marker (some sell tests one at a time), so this page cannot say whether they offer Vitamin D (25-Hydroxy). Check with them directly.
Life Extension Standard · Quest Health · Ultrahuman Blood Vision · Lifeforce · Hundred Health · Personalabs · Walk-In Lab · HealthLabs · WHOOP Specialized Panels · Marek Health Essential · Vitality Blueprint Upload
Experts discussing Vitamin D (25-Hydroxy)
Podcast episodes where clinicians and researchers cover this marker in depth. Curated by hand; an episode is listed only when the marker is a substantial topic, not a passing mention.
- Dr. Rhonda Patrick: Micronutrients for Health & LongevityDisclosure: Huberman Lab has been sponsored by Function Health, which appears in our blood-test comparisons.
- Check These Biomarkers on Your Next Blood Test
- How Vitamin D, Omega-3s, & Exercise May Increase Longevity
- Vitamin D's role in immune function
- Don't Die Podcast #4: The Biomarker Strategy That Made Bryan Johnson the World's Healthiest HumanDisclosure: This is Bryan Johnson's podcast; Johnson owns Blueprint, which appears in our blood-test comparisons.
Frequently Asked Questions
What is the optimal range for Vitamin D (25-Hydroxy)?
Published positions differ: >=20 ng/mL sufficient (NASEM (Institute of Medicine) dietary reference intakes); 30-100 ng/mL; deficiency below 20 (Endocrine Society clinical practice guideline (2011)). Named practitioners target: 40-60 ng/mL (Dr. Rhonda Patrick); 50-80 ng/mL (Life Extension); 50-70 ng/mL (Tracey O'Shea (Kresser Institute)). Lab reference interval: Deficient: <20 ng/mL, Insufficient: 20-29 ng/mL, Sufficient: 30-100 ng/mL. That is what a lab report flags against, not an optimal target.
Which blood test providers include Vitamin D (25-Hydroxy)?
17 of the 21 blood testing panels we itemize marker by marker include Vitamin D (25-Hydroxy) in their panels. This biomarker is widely available across major providers.
Related: YouBoost rates lifestyle and supplement interventions by evidence.
Medical Disclaimer
This information is for educational purposes only and is not medical advice. Always consult with a qualified healthcare provider about your specific health needs.
Last reviewed Sep 23, 2026 · First published Sep 30, 2025