Vitamin D (25-Hydroxy)
Essential vitamin for bone health and immunity
17 of 22 providers
Vitamins &Nutrients
Deficient:<20 ng/mL, Insufficient:20-29 ng/mL, Sufficient:30-100 ng/mL, Optimal:40-60 ng/mL
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.
Here's the critical insight:vitamin D deficiency is epidemic—an estimated 40-50% of the global population is deficient (<20 ng/mL), and insufficiency (<30 ng/mL) is even more common. Vitamin D is essential for bone health, immune function, cardiovascular health, mood, and much more. Low vitamin D is associated with increased risk of osteoporosis, fractures, autoimmune disease, infections, cardiovascular disease, cancer, and all-cause mortality. For longevity optimization, most functional medicine practitioners target 40-60 ng/mL, well above the "sufficient"threshold of 30 ng/mL.
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, osteomalacia in adults, and accelerates osteoporosis.
- Immune function:Vitamin D modulates both innate and adaptive immunity. Deficiency increases risk of respiratory infections (flu, COVID-19), autoimmune diseases (MS, type 1 diabetes, rheumatoid arthritis).
- Cardiovascular health:Vitamin D receptors are present in heart, blood vessels, and vascular smooth muscle. Deficiency associated with hypertension, heart failure, stroke.
- Cancer prevention:Vitamin D regulates cell growth, differentiation, and apoptosis. Higher levels (>40 ng/mL) associated with 20-30% lower risk of colorectal, breast, and prostate cancer.
- Mood and mental health:Vitamin D receptors in brain. Deficiency linked to depression, seasonal affective disorder, cognitive decline.
- Metabolic health:Vitamin D improves insulin sensitivity. Deficiency increases risk of type 2 diabetes and metabolic syndrome.
Optimal vs Standard Ranges
Optimal (Longevity)40-60 ng/mL▼
- Target range for longevity and disease prevention
- Associated with lowest all-cause mortality, optimal immune function, and cancer risk reduction
Sufficient (Standard)30-40 ng/mL▼
- Meets standard medical guidelines for bone health
- May be suboptimal for immune function and cancer prevention
Insufficient20-30 ng/mL▼
- Common range
- Bone health may be adequate but increased risk of infections, autoimmune disease, and suboptimal immunity
Deficient<20 ng/mL▼
- Frank deficiency
- Impairs calcium absorption, bone health, immune function
- Increases fracture risk, infections, and mortality
Scientific Evidence
Insufficient sun exposure:Living >35° latitude, winter months, indoor lifestyle, sunscreen use, clothing coverage.|Dark skin pigmentation:Melanin blocks UVB absorption. African Americans have 3-4x higher deficiency rates than Caucasians.|Obesity:Vitamin D sequestered in adipose tissue, lowering blood levels.|Aging:Elderly produce 75% less vitamin D from sun exposure than young adults.|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).
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.
Vitamin D Deficiency Prevalence
Vitamin D deficiency (<20 ng/mL) affects 40-50% of the global population, with higher rates in darker-skinned individuals, elderly, obese, and those living in northern latitudes. Insufficiency (<30 ng/mL) affects >50% of adults in the US and Europe, especially in winter.
Source:Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266-281. (PubMed)
Vitamin D and All-Cause Mortality
Meta-analyses of randomized controlled trials show vitamin D supplementation (800-2000 IU/day) reduces all-cause mortality by 5-7%. Observational studies show U-shaped curve:both deficiency (<20 ng/mL) and excess (>60 ng/mL) associated with higher mortality, with optimal around 40-50 ng/mL.
Vitamin D and Immune Function
Vitamin D enhances innate immunity (macrophages, antimicrobial peptides) and modulates adaptive immunity (T cells, B cells). Deficiency increases risk of respiratory infections by 30-50%. Supplementation (1000-4000 IU/day) reduces incidence of flu, colds, and COVID-19, especially in those with baseline deficiency.
Vitamin D and Bone Health
Vitamin D increases intestinal calcium absorption from 10-15% to 30-40%. Deficiency causes secondary hyperparathyroidism, accelerating bone loss. Vitamin D supplementation (800-2000 IU/day) + calcium (1000-1200 mg/day) reduces fracture risk by 20-30% in elderly.
Which Providers Test Vitamin D (25-Hydroxy)?
Full Provider Comparison
| Provider | Includes | Annual Cost | Biomarkers |
|---|---|---|---|
 Superpower | ✓ | $199 | 100+ (150 with ratios) |
 WHOOP Advanced Labs | ✓ | $349 | 65 |
 Labcorp OnDemand | ✓ | $398 | 30+ |
| ✓ | $486 | 40+ | |
| ✓ | $444 | 288 | |
| ✓ | $349 | 100+ | |
| ✓ | $761 | 54 | |
 Function Health | ✓ | $365 | 160+ |
| — | $250 | 65 | |
| ✓ | $495 | 70+ | |
| ✓ | $895 | 100+ | |
| ✓ | $1950 | 150+ | |
| ✓ | $375 | 80+ | |
| — | $Varies | 75+ | |
| ✓ | $190 | 100+ | |
| — | $99 | 50 | |
| ✓ | $124 | 60 | |
| ✓ | $199 | 50 | |
| ✓ | $499 | 120+ | |
| ✓ | $4188 | 70-80+ | |
| — | $375 | 85 | |
| — | $700 | 128 |
Frequently Asked Questions
What is Vitamin D (25-Hydroxy)?
Essential vitamin for bone health and immunity
What is the optimal range for Vitamin D (25-Hydroxy)?
The standard reference range for Vitamin D (25-Hydroxy) is Deficient:<20 ng/mL, Insufficient:20-29 ng/mL, Sufficient:30-100 ng/mL, Optimal:40-60 ng/mL. Optimal ranges may differ based on individual health goals and expert recommendations.
Which blood test providers include Vitamin D (25-Hydroxy)?
17 out of 22 blood testing providers include Vitamin D (25-Hydroxy) in their panels. This biomarker is widely available across major providers.
What category does Vitamin D (25-Hydroxy) fall under?
Vitamin D (25-Hydroxy) is categorized under Vitamins &Nutrients. This category includes biomarkers that help assess related aspects of health and wellness.
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:2026-02-20