Vitamin C (Ascorbic Acid)
Updated: 2025-10-07
🍊 Overview
Vitamin C (ascorbic acid) is an essential water-soluble antioxidant that humans cannot synthesize.
It plays a vital role in:
- Protecting cells from oxidative damage,
- Collagen synthesis and wound healing,
- Immune system support,
- And enhancing non-heme iron absorption from plant foods.
The best natural sources include fresh fruits and vegetables such as citrus, kiwi, bell peppers, strawberries, and broccoli.
Severe deficiency leads to scurvy, which can still occur in malnourished or elderly individuals.
🔬 Evidence Summary
| Health Domain | Strength of Evidence | Observed Effects |
|---|---|---|
| Immunity / Common cold | Moderate | Slightly reduces duration of colds (~1 day) but not overall incidence. |
| Collagen / Skin / Wound healing | High | Promotes collagen formation and tissue repair. |
| Iron absorption | High | Significantly increases non-heme iron absorption. |
| Antioxidant protection | High | Protects DNA, lipids, and proteins from oxidative stress. |
| Chronic disease / Cancer | Low | Mixed results, mainly for high-dose IV use. |
Overall rating: High for general health and deficiency prevention.
Moderate to low for infection prevention.
⚙️ Mechanism of Action
- Major antioxidant: Neutralizes free radicals and regenerates vitamin E.
- Collagen metabolism: Cofactor for proline and lysine hydroxylation enzymes.
- Immune function: Supports leukocyte activity and interferon production.
- Iron absorption: Converts ferric iron (Fe³⁺) into ferrous iron (Fe²⁺), which is more absorbable.
- Neurotransmission: Involved in norepinephrine synthesis and neuronal protection.
💊 Dosage & Forms
| Purpose | Typical Dose | Notes |
|---|---|---|
| Recommended Dietary Allowance (RDA) | M: 90 mg/day • F: 75 mg/day | Health Canada / WHO |
| General supplementation | 250–500 mg/day | Immune or antioxidant support |
| Deficiency correction | 100–500 mg/day for 1–3 months | To restore normal plasma levels |
| Upper intake limit (UL) | 2000 mg/day | Higher doses may cause digestive upset |
💡 Tip: Split doses (e.g., 250 mg morning + 250 mg evening) to improve absorption — it becomes saturated above 200 mg.
⚖️ Benefits vs Risks
| Benefits | Potential Risks |
|---|---|
| + Boosts immunity and wound healing | – Digestive upset at high doses |
| + Strong antioxidant protection | – Risk of oxalate kidney stones |
| + Enhances iron absorption | – May interfere with lab tests |
| + Supports skin and collagen | – Unnecessary at high doses if not deficient |
🤝 Useful Synergies
| Combination | Effect |
|---|---|
| Vitamin C + Zinc | Stronger immune defense. |
| Vitamin C + Collagen | Improves skin health and connective tissue repair. |
| Vitamin C + Iron (plant sources) | Doubles or triples non-heme iron absorption. |
| Vitamin C + Vitamin E | Complementary antioxidant regeneration. |
⚠️ Risks & Interactions
- Consult a doctor if you have kidney disease, kidney stones, or hemochromatosis.
- Very high doses may cause digestive issues or oxalate kidney stones.
- Doses >1 g/day may trigger diarrhea, nausea, or acid reflux.
- Increases non-heme iron absorption — avoid excess in iron overload conditions.
- May interfere with certain blood tests and high-dose IV cancer therapies.
✅ Quality Tips
- Prefer pure ascorbic acid or calcium/sodium ascorbate forms.
- Check for stability — some tablets oxidize quickly.
- Eat fresh fruits and vegetables raw or lightly cooked to preserve vitamin C (heat and air sensitive).
- Avoid mega-doses (>1 g/day) without medical supervision.
📚 References
⚠️ Educational information. Always seek professional advice.