✓ No active regulatory warningsFDA MedWatch, EMA EudraVigilance, WHO VigiBase, WADA Prohibited List · 2026-05-29
📰Read the full Vitamin C evidence review on GMJ News →Complete clinical article, references and updates on news.gmj.ge. This page is the structured safety summary.⚠ Doses above 2,000 mg/day increase calcium oxalate nephrolithiasis risk [1].
⚠ High-dose vitamin C can interfere with glucose monitoring in diabetic patients (falsely elevated readings) [1].
🥗 Food first — build your daily 90 mg/ 75 mg
Check the foods you regularly eat — the bar fills toward your daily target.
Red bell pepper (½ cup)95 mg
Orange juice (¾ cup)93 mg
Orange (1 medium)70 mg
Kiwifruit (1 medium)64 mg
Broccoli (½ cup cooked)51 mg
Strawberries (½ cup)49 mg
Brussels sprouts (½ cup)48 mg
Tomato juice (¾ cup)33 mg
Check your regular foods above
☑ Risk checker
Active smokers (require additional 35 mg/day) [1]
Passive smoke exposure [1]
Limited fruit and vegetable intake
Alcoholism [1]
Malabsorption disorders
Chronic kidney disease on dialysis [1]
Elderly with restricted diets
Select factors
🔬 Lab interpreter
Recommended test
Plasma ascorbic acid
Plasma ascorbic acid
Reference range / target
0.4–1.5 mg/dL (23–85 µmol/L normal). <0.2 mg/dL suggests depletion. <0.1 mg/dL = scurvy range [1]
0.4–1.5 mg/dL (23–85 µmol/L normal). <0.2 mg/dL suggests depletion. <0.1 mg/dL = scurvy range [1]
When to test
Suspected scurvy; malnutrition assessment; chronic smokers; malabsorption
Full lab monitoring ↓Suspected scurvy; malnutrition assessment; chronic smokers; malabsorption
⚕ For professionals — confirm ranges against your local laboratory.
Clinical verdict
Prophylactic supplementation (200 mg or more per day) reduces cold duration by 8% in adults and 14% in children but does not prevent colds [3]. Bioavailability plateaus above 200 mg per dose — split larger doses [1]. Co-prescribe with iron-rich meals to enhance non-heme iron absorption 2–3 fold [1]. Smokers require an additional 35 mg/day [1].
1 How much do I need?
👤 Adults: Specific dosage data under clinical review
👴 Elderly: Specific dosage data under clinical review
🤰 Pregnancy: Specific dosage data under clinical review
👦 Pediatric: See guidance
RDA: 15-25 mg for children 1-8 years, 45-75 mg for children 9-13 years, 65-75 mg for adolescents 14-18 years [1].
🏃 Athletes: Standard dose
⚖️ Obesity: Standard dose
Fat-soluble compounds may require dose adjustment in obesity.
🩺 Renal: Consult specialist
Dose adjustment may be needed in renal impairment.
🌱 Vegan: Standard dose
How to take
🍽 Timing: Can be taken any time. Divided doses (2–3× daily) maintain higher plasma levels than single large dose [1].
💊 With food: Take with meals to reduce GI discomfort. Take with iron-containing foods or supplements to enhance iron absorption [1].
🚫 Avoid: Do not take >500 mg at once (diminishing absorption returns). Avoid mega-doses (>2 g/day) in those with history of oxalate kidney stones or hemochromatosis [2].
2 Which form?
| Form | Bioavailability | Vegan | Cost |
|---|---|---|---|
| ['L-ascorbic acid', 'preferred', 'The biologically active form. Rapidly absorbed in the small intestine. Bioavailability decreases at doses above 200 mg due to saturable intestinal transport [1].'] | Standard | Check label | |
| ['Sodium ascorbate', '', 'Buffered form with reduced acidity. Preferred for individuals with gastric sensitivity. Contains 111 mg sodium per 1,000 mg.'] | Standard | Check label | |
| ['Liposomal vitamin C', '', 'Phospholipid-encapsulated form with enhanced absorption at higher doses. More expensive; evidence for clinical superiority is limited.'] | Standard | Check label |
3 Common questions
Can vitamin C prevent the common cold? ▼
Regular supplementation (200 mg or more per day) does not prevent colds but may reduce their duration by approximately 8% in adults and 14% in children, based on a Cochrane meta-analysis of 29 trials [3]. Taking vitamin C after cold symptoms begin has no significant effect on duration or severity.
How much vitamin C is too much? ▼
The upper tolerable limit is 2,000 mg per day for adults [1]. Doses above this may cause diarrhea, nausea, abdominal cramps, and increase the risk of calcium oxalate kidney stones. The kidneys excrete excess vitamin C when plasma levels exceed the renal threshold.
Is liposomal vitamin C better than regular vitamin C? ▼
Liposomal formulations may achieve higher plasma concentrations than standard oral vitamin C at equivalent doses, but clinical evidence of superior health outcomes is limited. Standard L-ascorbic acid at doses of 200 mg or less is nearly 100% bioavailable [1].
Do I need vitamin C supplements if I eat fruits and vegetables? ▼
Most individuals who consume five or more servings of fruits and vegetables daily obtain adequate vitamin C from diet alone. Supplementation is primarily indicated for smokers (who require an additional 35 mg per day), individuals with limited dietary variety, and those with malabsorption conditions [1].
4 Clinical evidence
Strong
Scurvy prevention and treatment [1]. Enhanced non-heme iron absorption when consumed with iron-rich meals, increasing absorption by 2-3 fold [1]. Shortened duration of common cold symptoms by 8% in adults when taken prophylactically (not after symptom onset), based on a Cochrane review of 29 trials involving 11,306 participants [3]. HIGH
Moderate
Reduced risk of cardiovascular disease in observational studies: individuals with highest plasma vitamin C had 25% lower CVD mortality versus lowest quintile [4]. Potential benefit in age-related macular degeneration progression when combined with vitamin E, beta-carotene, and zinc (AREDS formulation) [1]. MODERATE
Insufficient
5 Safety, toxicity & adverse events
Absolute contraindications
✕ Hemochromatosis or iron overload — vitamin C enhances iron absorption, worsening tissue iron deposition
Relative
⚠ History of oxalate kidney stones — high-dose C (>1,000 mg/day) increases urinary oxalate
⚠ G6PD deficiency — high-dose IV ascorbate can cause hemolytic anemia
⚠ CKD — impaired oxalate clearance increases stone risk
⚠ Concurrent use of aluminum-containing antacids — C increases aluminum absorption
🚩 Red flags
● Unexplained petechiae, bleeding gums, poor wound healing — consider scurvy even in developed countries (elderly, alcoholics, food desert populations) [1]
● Patient on bortezomib taking vitamin C supplements — may reduce chemotherapy efficacy [3]
● Chronic mega-dose vitamin C (>2 g/day) with recurrent kidney stones — oxalate nephropathy risk [2]
● G6PD deficiency patient receiving IV high-dose vitamin C — hemolysis risk (screen before IV therapy) [2]
● False-negative fecal occult blood test in patient taking >1 g/day vitamin C [2]
6 Interactions
Drug interactions
Bortezomib (Velcade) Major
Mechanism: In vitro evidence suggests vitamin C directly inactivates bortezomib's boronic acid pharmacophore. Clinical significance debated but avoidance recommended by manufacturer [3].
Warfarin Moderate
Mechanism: High-dose vitamin C (>1 g/day) may compete with warfarin for CYP metabolism or enhance warfarin clearance. Effect is inconsistent across studies [3].
Chemotherapy (general) Moderate
Mechanism: Theoretical concern that antioxidant properties may protect cancer cells from oxidative damage induced by certain chemotherapies. Evidence is mixed and agent-specific [4].
Iron supplements Beneficial
Mechanism: Vitamin C (200 mg) taken with non-heme iron enhances absorption by 2–6× via reduction of Fe³⁺ to Fe²⁺ and chelation preventing phytate/tannin binding [1].
7 Regulatory
United States (FDA): Dietary supplement (OTC). Qualified health claim for antioxidant vitamins and cancer risk (with significant scientific agreement disclaimer).
European Union (EFSA): Fifteen authorized health claims including immune function, collagen formation, energy metabolism, iron absorption, and antioxidant protection.
Japan (MHLW): Nutrient function claim permitted. Listed as essential nutrient in Japanese Dietary Reference Intakes.
South Korea (MFDS): Registered health functional food ingredient. Approved claims: antioxidant, immune function, connective tissue health.
8 US supplement products
5,317
on-market products containing Vitamin C (NIH DSLD)
Brands carrying Vitamin C (969)
Click a brand to see its Vitamin C products.
9 Frequently paired with
10 Cite this page
Vancouver: Pkhakadze G. Vitamin C — safety profile [Internet]. Tbilisi: PHIG; 2026 [cited 2026 Jun 16]. Available from: https://supplement.ge/ingredients/vitamin-c/
APA 7th: Pkhakadze, G. (2026). Vitamin C — Safety profile. Public Health Institute of Georgia. https://supplement.ge/ingredients/vitamin-c/
📋 Editorial information
Author: Prof. G. Pkhakadze, MD, MPH, PhD
Institution: Public Health Institute of Georgia (PHIG)
Affiliation: David Tvildiani Medical University (DTMU)
First published: January 2026
Last reviewed: 2026-05-29
Next review: December 2026
References: 4 cited sources
COI: SupplementIndex receives no funding from supplement manufacturers. All content independently authored by PHIG.
Process: Systematic literature review
📄 License & reuse
Published under Creative Commons Attribution 4.0 International (CC BY 4.0). You may share and adapt for any purpose with attribution.
Pkhakadze G. "Vitamin C — Safety Profile." SupplementIndex, PHIG, 2026. https://supplement.ge/ingredients/vitamin-c/ CC BY 4.0.
GP
Prof. G. Pkhakadze, MD, MPH, PhD
Professor of Public Health · Head of Department, DTMU
Editor-in-Chief, Georgian Medical Journal (ISSN 3088-4322)
Chair, Public Health Institute of Georgia · UEMS Public Health Section
Educational and public health purposes. CC BY 4.0. Consult your healthcare provider before starting any supplement. Corrections: info@accreditation.ge. Publisher: PHIG