Lever
Lifestyle
- Increase sun exposure
- Engage in outdoor physical activities
- Monitor and adjust vitamin D supplementation
Blutwerte · Marker
Vitamin D3 (25-OH)
25-Hydroxyvitamin D · Calcidiol · Cholecalciferol · 25-OH-D3
Vitamine & Nährstoffe
- Einheit:
- nmol/L
- Abbreviation
- 25(OH)D
The test quantifies the concentration of 25-Hydroxyvitamin D in the blood, reflecting vitamin D status.
Reference Ranges
Reference
50–125nmol/L
50
75
100
125
LowNormalHigh
Reference
Optimal
Unit · nmol/LReference ranges may vary by assay method and population. Consider seasonal and geographic factors.
Overview
Übersicht
Vitamin D3 (25-OH), also known as 25-Hydroxyvitamin D or Calcidiol, is a prehormone produced in the liver by hydroxylation of vitamin D3 (cholecalciferol). It is the main circulating form of vitamin D and is considered the best indicator of vitamin D status in the body. This biomarker reflects the amount of vitamin D produced in the skin from sunlight exposure and obtained from dietary sources. Clinically, 25(OH)D is crucial for calcium and phosphate homeostasis, influencing bone health and immune function. Deficiency is linked to conditions such as osteoporosis, rickets, and increased susceptibility to infections. Epidemiological studies have also associated adequate levels with reduced risks of autoimmune diseases, cardiovascular diseases, and certain cancers. For athletes and biohackers, maintaining optimal levels of 25(OH)D is important for muscle function, immune modulation, and possibly enhancing testosterone levels, as some studies suggest a correlation between vitamin D supplementation and increased testosterone in men. However, researchers note that assay variability and factors like skin pigmentation, latitude, and seasonal changes can affect 25(OH)D levels. Time-of-day and fasting do not significantly impact the test, but standardization of assays is essential for accurate assessment.
Klinische Bedeutung
Elevated 25(OH)D levels may indicate excessive supplementation or hypercalcemia, while reduced levels suggest vitamin D deficiency, potentially leading to bone disorders and increased disease risk.
Dynamics
Trend Interpretation
Rising Values
Progressively rising values may indicate excessive supplementation. Re-test in 3 months if levels exceed 125 nmol/L.
Falling Values
Falling values suggest worsening deficiency or malabsorption issues.
Re-test Interval
4 weeks if outside optimal range
Etiology
Causes — High & Low
Cause
Elevated Levels
- Excessive vitamin D supplementation
- Granulomatous diseases
- Primary hyperparathyroidism
- Certain lymphomas
- Williams syndrome
Cause
Low Levels
- Inadequate sunlight exposure
- Poor dietary intake
- Malabsorption syndromes
- Chronic kidney disease
- Liver dysfunction
Protocol
How to Optimize
Lever
Nutrition
- Consume fatty fish
- Include fortified foods
- Incorporate egg yolks
Lever
Supplementation
- Vitamin D3 supplements
- Cod liver oil
Note:
Consult a healthcare provider before starting supplementation, especially if on medications affecting calcium metabolism.
Testing Guidelines
✓Fasting Not Required
✓Not Time-Sensitive
Vitamin D levels can vary throughout the day; morning testing is recommended for consistency.
Testing Frequency
Annually for healthy adults, more frequently if managing deficiency.
Interfering Factors
- Assay variability
- Recent high-dose supplementation
Related Peptides & Hormones
Testosterone
hormoneCorrelated with
Open Research Questions
Current research suggests that there is significant variability in 25-hydroxyvitamin D (25[OH]D) measurements across different immunoassays, leading to debates about reference ranges and optimal targets for vitamin D status, particularly in specific populations like pregnant women. Researchers have not yet established standardized protocols for vitamin D testing, which could address discrepancies in results. Additionally, unanswered clinical questions remain regarding the long-term health impacts of varying 25(OH)D levels on conditions like osteoporosis and autoimmune diseases.
26 Research Publications
938
Total Citations
8
Human/RCT
2.7
Avg. Influence
2025
Latest
Sort
Filter
01Top
#01
Effect of vitamin D supplementation on testosterone levels in men.
HumanInfluence13.0
316
This study examined the effect of vitamin D supplementation on testosterone levels in healthy overweight men. Researchers found that vitamin D supplementation significantly increased total testosterone levels, bioactive testosterone, and free testosterone compared to the placebo group. Initial vitamin D levels were in the deficiency range, highlighting the potential impact of supplementation.
02Top
#02
Calcium and Bone Metabolism Indices.
ReviewInfluence5.0
128
Researchers discussed the critical role of calcium and phosphate in body functions, regulated by vitamin D and parathyroid hormone. The review emphasized the importance of laboratory tests, including 25-hydroxyvitamin D, in diagnosing metabolic bone diseases and monitoring calcium homeostasis.
03Top
#03
Epidemiology of vitamin D in health and disease.
ReviewInfluence2.0
88
This review explored the epidemiology of vitamin D in relation to various health conditions. Researchers found that adequate vitamin D levels are crucial for reducing risks of bone fractures, autoimmune diseases, and certain cancers, while noting widespread vitamin D insufficiency in high latitude populations.
04
#04
Vitamin D in Cardiovascular Disease.
ReviewInfluence1.0
67
This review explored the relationship between vitamin D and cardiovascular disease. Researchers found associations between vitamin D deficiency and increased inflammatory processes that may contribute to atherosclerosis, although the role of 25-hydroxyvitamin D as a biomarker for cardiovascular risk remains unclear.
05
#05
Measurement of vitamin D and its metabolites (calcidiol and calcitriol) and their clinical significance.
Schmidt-Gayk H, et al. · Scandinavian journal of clinical and laboratory investigation. Supplementum · 1997
Review
62
Researchers investigated the clinical significance of measuring vitamin D and its metabolites. They found that plasma concentrations of 25-hydroxyvitamin D (25[OH]D) are the best indicators of vitamin D deficiency. The study also highlighted that vitamin D supplementation is recommended for individuals with 25(OH)D levels below 50 nmol/L.
Key findings
- 01Researchers observed that 25-hydroxyvitamin D is the best marker for assessing vitamin D deficiency.
- 02They found that many people in Europe and North America have suboptimal vitamin D levels from November to April.
- 03The study indicated that vitamin D metabolism is affected by kidney health and the body's calcium and phosphate supply.
06
#06
Measurement of circulating 25-hydroxyvitamin D: A historical review.
ReviewInfluence1.0
53
This historical review examined the evolution of methods for measuring 25-hydroxyvitamin D. Researchers highlighted the introduction of liquid chromatography-tandem mass spectrometry as a more precise method, while also stressing the need for standardization to ensure consistent clinical decision thresholds.
07
#07
25-Hydroxyvitamin D: analysis and clinical application.
Review
38
This review focused on the clinical applications of 25-hydroxyvitamin D testing. Researchers noted that despite improvements in testing methodologies, significant biases exist among different assays, underscoring the need for standardization to accurately assess vitamin D status.
08
#08
25-Hydroxyvitamin D Testing: Immunoassays Versus Tandem Mass Spectrometry.
ReviewInfluence2.0
31
Researchers compared automated immunoassays and tandem mass spectrometry for measuring 25-hydroxyvitamin D. The study emphasized the need for harmonization of testing methods due to significant differences in results, which are critical for making clinical decisions regarding vitamin D deficiency.
09
#09
Serum Vitamin D as a Biomarker in Autoimmune, Psychiatric and Neurodegenerative Diseases.
ReviewInfluence1.0
30
Researchers summarized studies on serum 25-hydroxyvitamin D levels in autoimmune, psychiatric, and neurodegenerative diseases. They found an association between low 25(OH)D levels and the prevalence of these conditions, but the clinical utility of 25(OH)D as a biomarker remains unclear due to variability in study methods.
10
#10
Vitamin D in adolescents: Are current recommendations enough?
ReviewInfluence2.0
25
This review addressed the importance of vitamin D for bone development in adolescents. Researchers highlighted the high prevalence of vitamin D inadequacy in this population and noted that current intake recommendations may not be sufficient to achieve optimal 25-hydroxyvitamin D levels for bone health.
Publication Trend
Research publications about Vitamin D3 (25-OH) over time
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