Vitamin D (25-OH)

Introduction

In the world of functional medicine, understanding the role and importance of biomarkers is crucial for both practitioners and patients. One such vital biomarker is Vitamin D (25-OH), which plays a significant role in maintaining various physiological processes. As a Nurse Practitioner with an autonomous practice in Florida, I aim to provide a clear, educational overview of Vitamin D (25-OH), its background, clinical implications, and factors affecting its levels.

Background of Vitamin D (25-OH)

Vitamin D is a fat-soluble vitamin essential for maintaining healthy bones and supporting immune function. It exists in several forms, but the most important for assessing vitamin D status is 25-hydroxyvitamin D, commonly referred to as Vitamin D (25-OH). This form is the main circulating form in the blood and serves as the best indicator of overall vitamin D status.

Vitamin D can be obtained from sun exposure, dietary sources, and supplements. However, despite its availability, vitamin D deficiency remains a common global health issue linked to various disorders, including some cancers, hypertension, cardiovascular disease, inflammation, and mental health conditions such as depression.

Discussion on Vitamin D (25-OH) Testing

Why Test for Vitamin D (25-OH)?

Testing for Vitamin D (25-OH) is crucial for identifying deficiencies and understanding potential health risks associated with low vitamin D levels. It is particularly important in diagnosing conditions like hypercalcemia (high calcium levels) or hypocalcemia (low calcium levels), which can significantly impact health.

The Process of Testing

The Vitamin D (25-OH) test measures the concentration of 25-hydroxyvitamin D in the blood. This test is considered the standard for assessing vitamin D status because it reflects the total amount of vitamin D from dietary intake, supplements, and skin synthesis.

Ranges and Interpretation

• U.S. Units Standard Range: 30.00 – 100.00 ng/mL
  
• International Units Standard Range: 74.88 – 249.60 nmol/L
  
• Optimal Range: 50.00 – 90.00 ng/mL (124.80 – 224.64 nmol/L)
  
  

Maintaining levels within this optimal range supports bone health, immune resilience, and overall well-being.

Clinical Implications of Vitamin D (25-OH)

Low Vitamin D Levels

A decreased serum Vitamin D level often indicates deficiency and is associated with:

• Diabetes mellitus
  
• Certain cancers (e.g., breast, colon)
  
• Hypertension and cardiovascular disease
  
• Chronic inflammation and musculoskeletal pain
  
  

High Vitamin D Levels

Conversely, increased serum Vitamin D levels usually result from excessive supplementation. Because Vitamin D is fat-soluble, it can accumulate, leading to hypercalcemia and other complications if not monitored.

Interfering Factors

Falsely Decreased Levels

• Malabsorption Disorders: Celiac disease, Crohn’s disease
  
• Obesity: Sequestration in adipose tissue
  
• Liver or Kidney Disease: Impaired conversion to active forms
  
  

Falsely Increased Levels

• Assay Variability: Different laboratory methods
  
• Altered Binding Proteins: Changes in Vitamin D–binding protein levels
  

Drug Causes of Decreased and Increased Levels

• Decreased Levels:
  
  • Anticonvulsants (phenytoin, phenobarbital)
    
  • Glucocorticoids
    
    
• Increased Levels:
  
  • Thiazide diuretics
    
    

Conclusion

In conclusion, a comprehensive evaluation by a functional medicine nurse practitioner in Florida facilitates identification of vitamin D–related and systemic imbalances driving musculoskeletal, immunologic, and metabolic dysfunction. By integrating evidence-based therapies with longevity medicine and IV therapy services, we offer patients a preventive framework to rebuild resilience and optimize wellness. Call 904-799-2531 or schedule online to request your personalized bone and immune health assessment.

Further Reading

1. Holick MF. “Vitamin D Deficiency.” N Engl J Med. 2007;357(3):266–281. PubMed: https://pubmed.ncbi.nlm.nih.gov/17634462/
   
2. Autier P, Gandini S. “Vitamin D Supplementation and Total Mortality: A Meta-analysis of Randomized Controlled Trials.” Arch Intern Med. 2007;167(16):1730–1737. PubMed: https://pubmed.ncbi.nlm.nih.gov/17768268/
3. Park Y, et al. “Serum 25-Hydroxyvitamin D Concentration and Cause-Specific Mortality.” Nutrients. 2021;13(4):1434. PubMed: https://pubmed.ncbi.nlm.nih.gov/33924748/