What Does Vitamin D Do?
Vitamin D is a fat-soluble vitamin that functions more like a hormone. It plays critical roles in:
- Bones: Regulates calcium and phosphate absorption; essential for bone mineralisation. Deficiency causes rickets in children and osteomalacia (soft bones) in adults
- Immunity: Activates immune cells; low levels linked to increased infections and autoimmune diseases
- Mood: Vitamin D receptors are present in brain regions involved in depression regulation
- Muscle function: Necessary for muscle contraction and strength; deficiency causes proximal muscle weakness
- Cardiovascular health: Low levels associated with increased cardiovascular risk
25-OH Vitamin D Test Results Explained
| Category | Level (ng/mL) | Level (nmol/L) | Clinical Significance |
|---|---|---|---|
| Severe Deficiency | <10 ng/mL | <25 nmol/L | High risk of osteomalacia, myopathy, significant symptoms |
| Deficiency | 10–20 ng/mL | 25–50 nmol/L | Requires treatment with supplementation |
| Insufficiency | 20–30 ng/mL | 50–75 nmol/L | Suboptimal; supplementation beneficial especially in high-risk groups |
| Sufficient | 30–60 ng/mL | 75–150 nmol/L | Normal range for most adults |
| Optimal | 40–60 ng/mL | 100–150 nmol/L | Associated with best health outcomes |
| Potential Toxicity | >100 ng/mL | >250 nmol/L | Risk of hypercalcaemia; avoid supplements causing these levels |
Symptoms of Vitamin D Deficiency
- Bone pain and tenderness (especially in back, legs, ribs)
- Proximal muscle weakness (difficulty climbing stairs, rising from a chair)
- Fatigue and generalised tiredness
- Frequent infections (recurrent respiratory infections, colds)
- Depressed mood, low energy
- Hair loss (in severe deficiency)
- Impaired wound healing
Who is Most at Risk?
| Risk Factor | Why it Causes Deficiency |
|---|---|
| Limited sun exposure (indoor lifestyles in India) | Sunlight on skin is the primary source of vitamin D synthesis |
| Dark skin tone | Higher melanin reduces vitamin D synthesis efficiency |
| Obesity (BMI >30) | Vitamin D is sequestered in fat tissue, reducing circulating levels |
| Malabsorption syndromes (coeliac, Crohn's) | Reduced absorption from gut; fat-soluble vitamins affected |
| Chronic kidney disease | Kidneys activate vitamin D; impaired activation in CKD |
| Elderly individuals | Reduced skin synthesis, less outdoor activity, decreased dietary intake |
Treatment
Mild-to-Moderate Deficiency (10–20 ng/mL)
Standard Indian protocol: Cholecalciferol (Vitamin D3) 60,000 IU once a week for 8 weeks (loading dose), then maintenance of 1,000–2,000 IU per day. Many doctors prescribe once-monthly sachets (60,000 IU) for maintenance after loading. Always take with a fatty meal as it is fat-soluble.
Severe Deficiency (<10 ng/mL)
Higher loading doses may be needed — some protocols use 60,000 IU 2–3 times per week for 4–8 weeks under medical supervision. Intramuscular vitamin D injections are sometimes used when absorption is impaired. Calcium supplementation alongside may be recommended.
Sunlight Exposure
Natural synthesis: 20 minutes of sun exposure 3 times per week with face, arms and legs exposed (not through glass) between 11am–3pm in India. Sunscreen blocks synthesis. This approach alone is often insufficient in urban India due to air pollution and indoor lifestyles.
Monitoring
Recheck 25-OH Vitamin D levels 3 months after starting treatment to assess response. Once in the sufficient range, annual monitoring is usually sufficient unless you have an ongoing risk factor like malabsorption or kidney disease.
Questions to Ask Your Doctor
- What is my exact vitamin D level, and which category does it fall in?
- What dose of supplementation do you recommend for my level?
- Should I also take calcium, and how much?
- When should I recheck my vitamin D level?
- Is my deficiency causing my fatigue or bone pain?