Vitamin D

Vitamin D is a fat-soluble micronutrient essential for:

• Calcium & phosphorus balance—critical for bone mineralization and dental health

• Immune regulation—modulates both innate and adaptive immune responses

• Muscle function—supports strength and coordination

• Cellular growth—affects cell differentiation and may play a role in cancer prevention

Sources

• Sunlight: UVB rays convert 7-dehydrocholesterol in skin to cholecalciferol (D₃)

• Diet: fatty fish (salmon, mackerel), beef liver, egg yolks, fortified milk and cereals

• Supplements: available as vitamin D₂ (ergocalciferol) or D₃ (cholecalciferol)

Normal & Abnormal Serum Levels

Measured as 25-hydroxyvitamin D [25(OH)D] in ng/mL:

• Optimal: 20–50 ng/mL

• Insufficiency: 10–20 ng/mL

• Severe deficiency: 5–10 ng/mL

• Very severe deficiency: < 5 ng/mL

• Toxicity: > 150 ng/mL

Who Should Test & Why?

A Vitamin D assay helps diagnose or monitor:

• Skeletal disorders: osteoporosis, osteomalacia, rickets

• Autoimmune conditions: multiple sclerosis, rheumatoid arthritis

• Cardiometabolic health: hypertension, diabetes risk

• Cancer risk assessment: breast, colon, and prostate cancers

Signs & Symptoms

Test Procedure

1. Sample: a single blood draw (serum)

2. Analyte: 25-hydroxyvitamin D

3. Turnaround: typically 1–2 business days

Frequently Asked Questions

1. What causes Vitamin D deficiency?
   Limited sun exposure, low dietary intake, malabsorption syndromes, and certain medications (e.g., anticonvulsants).

2. How can I boost my Vitamin D naturally?
   Aim for 10–30 minutes of midday sun several times weekly; eat fatty fish, fortified foods; discuss supplements with your provider.

3. Can too much Vitamin D harm me?
   Yes—excessive intake can cause hypercalcemia, leading to kidney stones, vascular calcification, and cardiac issues.

4. Who is at highest risk?
   Older adults, individuals with darker skin, those living at high latitudes or indoors, and people with gastrointestinal malabsorption.

5. How often should levels be checked?
   At-risk patients: every 6–12 months. Others: as clinically indicated (e.g., bone disease monitoring).