Vitamin C Dosage Calculator
An essential water-soluble antioxidant and enzyme cofactor. Required for collagen synthesis, immune function, and iron absorption. Widely used for cold prevention and skin health.
What is Vitamin C?
Vitamin C (ascorbic acid) is an essential water-soluble vitamin that humans cannot synthesise endogenously — making dietary or supplemental intake mandatory. It serves as a potent reducing agent (electron donor) in enzymatic reactions including collagen hydroxylation (via prolyl and lysyl hydroxylase), carnitine biosynthesis, norepinephrine synthesis, and regeneration of vitamin E from its oxidised form. As an antioxidant, it scavenges reactive oxygen species in aqueous compartments (plasma, cytosol) and enhances neutrophil and lymphocyte function. The RDA is 75–90 mg/day for adults; plasma saturation occurs at approximately 400 mg/day, above which absorption efficiency drops sharply and excess is renally excreted. For immune support and antioxidant effects, 500–1,000 mg/day is the most evidence-supported supplemental range. Divided dosing (e.g., 500 mg twice daily) maintains steadier plasma levels than a single large dose.
How to Take Vitamin C
RDA: 75–90 mg/day. For supplementation: 500–1,000 mg/day in 1–2 divided doses. Liposomal vitamin C offers higher cellular delivery than standard ascorbic acid, particularly relevant for doses > 1,000 mg. Buffered forms (sodium ascorbate, calcium ascorbate) are better tolerated for individuals with sensitive stomachs. Megadose protocols (> 2,000 mg/day) do not provide proportional additional benefit due to intestinal absorption saturation and carry increased risk of GI upset and kidney stones.
Timing Recommendations
Take with meals to improve tolerability. Co-administration with iron supplements significantly enhances non-haem iron absorption. Avoid megadoses (> 1,000 mg) in a single sitting — split into smaller doses across the day.
Potential Side Effects & Safety
Doses above the intestinal absorption threshold (~1,000–2,000 mg single dose) cause osmotic diarrhoea ("bowel tolerance effect"). Chronic megadosing (> 2,000 mg/day) is associated with increased oxalate kidney stone risk in predisposed individuals. High-dose vitamin C can interfere with glucose meter accuracy (falsely elevated readings) in people with diabetes.
Who should avoid Vitamin C?
History of calcium oxalate kidney stones: limit supplemental intake to ≤ 500 mg/day. Haemochromatosis: high vitamin C dramatically increases iron absorption — use cautiously with medical supervision. G6PD deficiency: very high IV doses (not oral) can cause haemolytic anaemia.
Best Stacks with Vitamin C
Vitamin C + zinc (classic immune stack). Vitamin C + iron (enhances non-haem iron absorption 2–3×). Vitamin C + collagen peptides (required cofactor for collagen hydroxylation — take together for skin/joint benefits). Vitamin C + vitamin E (mutually regenerate each other's antioxidant capacity).
Scientific References
All dosage recommendations are grounded in peer-reviewed research.
- 1Vitamin C and Immune Function
Nutrients · 2017
- 2A systematic review and meta-analysis on vitamin C supplementation and upper respiratory tract infections
European Journal of Clinical Nutrition · 2019
Vitamin C Dosage Calculator
Fixed dosage — independent of body weight
Your recommended daily dosage
Formula: RDA 75–90 mg/day | Supplemental sweet spot: 500–1,000 mg/day split into 2 doses
Safety notes
- Do not exceed 2,000 mg/day (Tolerable Upper Intake Level) — higher doses cause diarrhoea and increase kidney stone risk.
- Split doses across the day; intestinal absorption saturates above ~500 mg per single dose.
- History of kidney stones? Limit to ≤ 500 mg/day and stay well hydrated.
- High-dose vitamin C can falsely elevate blood glucose readings on some glucometers.
This calculator provides general guidance only. Always consult a qualified healthcare professional before starting any supplement.