Vitamin D Need

Introduction

Vitamin D is often referred to as the “sunshine vitamin,” but its role in human health extends far beyond supporting bone density. As a Nurse Practitioner with autonomous practice in Florida, I regularly assess vitamin D status in patients presenting with fatigue, recurrent infections, musculoskeletal pain, or even mood disorders. Despite ample sunlight in our region, deficiency and insufficiency remain common—and frequently overlooked—drivers of chronic health conditions.
In functional medicine, vitamin D is viewed not merely as a nutrient, but as a prohormone with widespread biological influence. Understanding how to evaluate and address vitamin D need can make a significant difference in your overall health trajectory.

Background

Vitamin D exists in two primary forms: D2 (ergocalciferol) from plant-based sources and fortified foods, and D3 (cholecalciferol), synthesized in the skin in response to UVB radiation from sunlight and present in animal-based foods. Once in the body, vitamin D undergoes two critical hydroxylations: first in the liver to form 25-hydroxyvitamin D [25(OH)D], and then in the kidneys to form the biologically active 1,25-dihydroxyvitamin D [1,25(OH)₂D].
This hormone-like compound plays essential roles in:

• Calcium and phosphate homeostasis
  
• Bone mineralization and remodeling
  
• Immune Function modulation
  
• Inflammation regulation
  
• Cellular differentiation and proliferation
  
  

Due to its far-reaching effects, a deficiency in vitamin D contributes to much more than bone weakness—it has systemic consequences.

Signs and Symptoms of Deficiency

Vitamin D deficiency can present subtly, often under the radar of conventional screenings. Common symptoms include:

• Bone pain and muscle weakness: Often mistaken for fibromyalgia or general aging.
  
• Fatigue and low energy: Due to impaired mitochondrial function and immune burden.
  
• Frequent infections: Including respiratory illnesses, sinusitis, or slow recovery from common colds.
  
• Mood changes: Low vitamin D levels are consistently correlated with depression and seasonal affective disorder (SAD).
  
• Poor wound healing and skin issues: A result of impaired cell repair and inflammatory dysregulation.
  
  

These nonspecific symptoms can be easily missed, making lab evaluation essential for proper diagnosis and management.

Diagnostic Evaluation

The gold standard for evaluating vitamin D status is the 25(OH)D blood test. This test measures the circulating storage form of vitamin D and provides the most reliable reflection of the body’s vitamin D reserves.

Clinical Ranges

Additional assessments may include:

• Bone density scan (DEXA) for patients at risk of osteoporosis or osteopenia (Bone Health).
  
• Calcium and phosphorus levels to monitor potential effects on mineral metabolism.
  
• PTH to evaluate secondary hyperparathyroidism.
  
  

Common Causes of Deficiency

Understanding the root causes of vitamin D deficiency is essential to restoring optimal levels. These may include:

1. Limited Sun Exposure
   
   • Sedentary indoor lifestyles
     
   • High-factor sunscreen use
     
   • Geographic latitude or seasonal changes
     
   • Clothing that limits skin exposure
     
2. Dietary Insufficiency
   
   • Low intake of D-rich foods (fatty fish, egg yolks, liver, fortified dairy)
     
   • Vegan or vegetarian diets without supplementation
     
3. Malabsorption Syndromes
   
   • Celiac disease, Crohn’s disease
     
   • Post-bariatric surgery
     
4. Organ Dysfunction
   
   • Chronic kidney disease (impaired hydroxylation)
     
   • Liver dysfunction (impaired 25(OH)D conversion)
     
5. Obesity
   
   • Sequestration in adipose tissue reduces bioavailability
     
6. Aging
   
   • Reduced skin synthesis
     
   • Decreased renal and hepatic conversion efficiency
     
     

Drug-Induced Interference

Several pharmaceutical agents are known to interfere with vitamin D metabolism or absorption:

• Anticonvulsants (e.g., phenytoin, phenobarbital)
  
• Glucocorticoids (chronic use reduces activity)
  
• Orlistat (inhibits fat-soluble vitamin absorption)
  
• Cholestyramine (binds bile acids, reducing uptake)
  
• Some antifungals and HIV/AIDS therapies
  
  

Clinical Implications

Vitamin D deficiency is not only about bone density—its systemic effects include:

1. Bone Health
   
   • Rickets in children
     
   • Osteomalacia in adults
     
   • Osteoporosis and fracture risk
     
2. Autoimmune Regulation
   
   • Linked to MS, RA, type 1 diabetes
     
3. Cardiovascular Function
   
   • Associated with hypertension, endothelial dysfunction
     
4. Immune Function
   
   • Modulates innate and adaptive responses, lowers risk/severity of respiratory infections
     
5. Mental Health
   
   • Correlated with depression, anxiety, cognitive decline
     
     

Functional Medicine Approach

At Intercoastal Health, we take a root-cause approach to nutrient optimization:

1. Nutritional Counseling
   
   • Wild-caught salmon, sardines, egg yolks, fortified plant milks
     
   • Address gut health if malabsorption is suspected
     
2. Lifestyle Optimization
   
   • Safe sun exposure (~15–30 minutes/day without sunscreen, as tolerated)
     
   • Increase outdoor activity
     
3. Supplementation
   
   • Vitamin D3 (2,000–5,000 IU/day maintenance; higher for repletion)
     
   • Pair with Vitamin K2 (MK-7) to direct calcium into bone
     
   • Re-test every 8–12 weeks
     
4. Address Underlying Causes
   
   • Evaluate GI pathology, chronic inflammation, or drug interactions
     
   • Ensure adequate magnesium for activation

Conclusion

A comprehensive evaluation by a functional medicine nurse practitioner in Florida identifies and corrects root-cause drivers of Vitamin D insufficiency. By integrating evidence-based nutrition guidance with IV Therapy and Regenerative Medicine services—where rapid nutrient replenishment and tissue support are paramount—we offer a preventive, regenerative framework to optimize bone health, immune resilience, and cardiovascular well-being. Call (904) 799-2531 or schedule online.

Further Reading

• Holick MF. “Vitamin D Deficiency.” N Engl J Med. 2007;357(3):266–281. https://doi.org/10.1056/NEJMra070553
  
• Autier P, Boniol M, Pizot C, Mullie P. “Vitamin D Status and Ill Health: A Systematic Review.” Lancet Diabetes Endocrinol. 2014;2(1):76–89. https://doi.org/10.1016/S2213-8587(13)70165-7
  
• Pilz S, Tomaschitz A, Grübler MR, Verheyen N, März W. “Vitamin D, Cardiovascular Disease and Mortality.” Clin Chem. 2011;57(5):934–945. https://doi.org/10.1373/clinchem.2011.165749
• Prietl B, Treiber G, Pieber TR, Amrein K. “Vitamin D and Immune Function.” Nutrients. 2013;5(7):2502–2521. https://doi.org/10.3390/nu5072502