25-Hydroxyvitamin D (25(OH)D)
25-Hydroxyvitamin D is the primary circulating storage metabolite of vitamin D, reflecting cutaneous UVB synthesis and dietary intake before final renal activation to 1,25(OH)2D.
Standard vs. Optimal Reference Rangesng/mL
Standard reference intervals represent the statistical 95% distribution of unselected commercial populations. Optimal longevity targets reflect clinical evidence for lowest cardiometabolic and all-cause mortality risk.
Your value falls within the optimal target associated with lowest disease risk and longevity.
30 - 100 ng/mL (Deficient: < 20 ng/mL)
General reference distribution across unselected commercial populations.
50 - 70 ng/mL
Concentration target associated with minimal all-cause cardiometabolic mortality.
Molecular Mechanism & Clinical Purpose
Synthesized in skin or absorbed enterically, cholecalciferol is 25-hydroxylated by CYP2R1 in the liver. In target tissues and kidneys, CYP27B1 converts 25(OH)D to calcitriol, which binds the nuclear Vitamin D Receptor (VDR) to regulate >3% of the human genome.
Differential Diagnosis
Elevated Levels (25(OH)D High)
- •Excessive exogenous Vitamin D3 supplementation
- •Granulomatous diseases (Sarcoidosis, Tuberculosis - dysregulated 1-alpha-hydroxylase)
Low Levels (25(OH)D Low)
- •Inadequate sunlight exposure / Winter latitudes
- •Malabsorption syndromes (Celiac, Crohn, bariatric surgery)
- •Hepatic failure (impaired 25-hydroxylation)
- •Obesity (adipose tissue sequestration)
Technical Reference & Deep Dive
Biochemistry & Enzymatic Pathways
Longevity Risk Architecture & Epidemiology
Pre-Analytical Caveats & Diagnostic Workup
Pre-Analytical Considerations:
Standard 10 to 12 hour overnight fast is recommended; avoid high-dose vitamin and mineral supplements for 24 hours prior to blood draw. Protect light-sensitive specimens (such as Vitamin B6, B12, and Folate) from ultraviolet light exposure by using amber collection tubes. Centrifuge and separate serum or plasma promptly to prevent in vitro leakage of intracellular minerals (e.g. magnesium, potassium) from red blood cells.
Reflexive Testing Protocol:
- Functional metabolic surrogate markers (Methylmalonic Acid for B12, Homocysteine for B6/B12/Folate, Red Blood Cell Magnesium)
- Complete Metabolic Panel and Ionized Calcium to evaluate electrolyte and mineral balance
- Celiac disease serology (Tissue Transglutaminase IgA with Total IgA) to screen for occult enteropathic malabsorption
- Parathyroid Hormone (PTH) and 24-Hour Urine Calcium quantification in cases of abnormal Vitamin D or calcium homeostasis
- Comprehensive Nutritional & Heavy Metal Trace Element panel via ICP-MS if multiple deficiencies are present
Clinical Citations & Primary Literature (1)
- [1]Vitamin D and Longevity: A Global Meta-Analysis of Randomized Controlled Trials - Lancet Diabetes & Endocrinology (2021). PMID: 33930321
Associated Longevity Guides & Clinical Calculators
Medicine 3.0Explore comprehensive evidence-based clinical protocols, testing costs, and algorithmic calculators that incorporate 25-Hydroxyvitamin D (25(OH)D) into overall healthspan optimization.