Vitamin D (D2 & D3)
Updated: 2025-10-07
☀️ Overview
Vitamin D is a fat-soluble vitamin essential for bone, muscle, and immune health.
It acts like a hormone, regulating calcium and phosphorus balance, both crucial for skeletal strength.
The body naturally produces it through skin exposure to UVB sunlight, but deficiency is frequent in northern climates or during the winter.
It is also found in fatty fish, egg yolk, liver, and fortified foods.
🔬 Evidence Summary
| Health Domain | Strength of Evidence | Observed Effects |
|---|---|---|
| Bone & Muscle Health | High | Maintains bone density, prevents rickets and osteomalacia. |
| Immunity & Infections | Moderate | Slightly reduces the risk of seasonal respiratory infections. |
| Mood / Depression | Moderate to Low | May support mood regulation and circadian balance. |
| Chronic Disease Prevention | Low | Conflicting data (cancer, diabetes, cardiovascular disease). |
Overall Rating: High for bone and immune support, low for systemic disease prevention.
⚙️ Mechanism of Action
- Calcium & phosphorus absorption: Increases intestinal calcium transporters.
- Bone health: Works with parathyroid hormone to maintain bone mineralization and prevent fractures.
- Muscle function: Supports muscle contraction and prevents weakness linked to deficiency.
- Immune modulation: Regulates cytokine production and enhances innate immunity (macrophages, antimicrobial peptides).
- Brain function: May influence neurotransmitters such as serotonin and dopamine.
💊 Dosage & Forms
| Purpose | Typical Dose | Notes |
|---|---|---|
| Recommended Dietary Allowance (RDA) | 600 IU/day (15 µg) | Adults aged 1–70 years |
| Over 70 years old | 800 IU/day (20 µg) | For bone and muscle maintenance |
| Winter or low sunlight exposure | 400–1000 IU/day | Common range in Canada |
| Deficiency correction (under supervision) | 2000–4000 IU/day | Adjusted based on blood tests |
| Upper Intake Limit (UL) | 4000 IU/day (100 µg) | Do not exceed without supervision |
💡 Tip: Vitamin D₃ (cholecalciferol) is 2–3 times more bioavailable than D₂ (ergocalciferol).
Take it with a fat-containing meal to improve absorption.
⚖️ Benefits vs Risks
| Benefits | Potential Risks |
|---|---|
| + Maintains bone density and strength | – Hypercalcemia risk with overdose |
| + Supports immune defense | – Fatigue, nausea, cardiac rhythm disturbances if excessive |
| + Prevents rickets and osteomalacia | – Drug interactions (e.g., corticosteroids, anticonvulsants) |
| + May support mood and muscle function | – Requires blood monitoring of 25(OH)D |
🤝 Useful Synergies
| Combination | Effect |
|---|---|
| Vitamin D + Calcium | Major synergy for bone strength. |
| Vitamin D + Magnesium | Improves metabolic activation and efficiency. |
| Vitamin D + Vitamin K2 | Helps direct calcium to bones instead of arteries. |
| Vitamin D + Omega-3 | Complementary support for immunity and inflammation. |
⚠️ Risks & Interactions
- Consult a healthcare provider if you have kidney, liver, or granulomatous diseases (e.g., sarcoidosis), or during pregnancy.
- Chronic overdose may cause hypercalcemia, kidney stones, or cardiac arrhythmias.
- Corticosteroids, orlistat, and some anticonvulsants can reduce absorption or activation.
- May potentiate the effects of digoxin or high-dose calcium supplements.
✅ Quality Tips
- Prefer natural D₃ sources (cod liver oil, lanolin, lichen-based for vegans).
- Avoid mega-doses (>4000 IU/day) unless prescribed.
- Check your 25(OH)D blood level annually (optimal: 30–60 ng/mL).
- Oil-based drops have better absorption than dry tablets.
📚 References
⚠️ Educational information. Always seek professional advice.