Vitamin C for Upper Respiratory Tract Infections
BResearch suggests regular vitamin C supplementation may reduce cold duration by approximately 8% in adults and 14% in children. Supplementation at 1g+/day is associated with reduced severity of cold symptoms. Notably, vitamin C started after symptom onset does not appear to be effective.
The Bottom Line
Research suggests regular vitamin C supplementation may reduce cold duration by approximately 8% in adults and 14% in children. Supplementation at 1g+/day is associated with reduced severity of cold symptoms. Notably, vitamin C started after symptom onset does not appear to be effective.
Key Study Findings
Population: Elite/professional cyclists nutrition review
Population: Children with inflammatory bowel disease (review)
Population: Large genetic cohort (MR analysis)
Population: COVID-19 patients with gut dysbiosis
Population: Broiler chickens
Population: None
Key Statistics
30
Studies
10000
Participants
Positive
Grade
Referenced Papers
Dosage & Usage
mg = milligrams · mcg = micrograms (1,000× smaller) · IU = International Units
Commonly Used Dosages
- general:
- 75-90 mg/day
- acuteillness:
- 1,000-2,000 mg/day
- immunesupport:
- 200-1,000 mg/day
Upper limit: 2,000 mg/day
Dosages Studied in Research
| Dosage | Duration | Effect | N |
|---|---|---|---|
| None | -- | Mixed | -- |
| None | -- | Neutral | -- |
| 12 circulating micronutrients | -- | Mixed | -- |
| Probiotics, nutraceuticals | -- | Positive | -- |
| None | -- | Positive | -- |
| 12.5 billion cfu/d | 24 weeks | Mixed | 171 |
| 45% | 988 weeks | Positive | 26282 |
| None | 13.0 weeks | Mixed | 3135 |
Best taken: With meals; divide doses >500 mg for better absorption
Safety & Side Effects
Reported Side Effects
- ⚠ Gastrointestinal distress (nausea, diarrhea, cramps) at high doses
- ⚠ Increased risk of kidney stones in susceptible individuals
- ⚠ Interference with certain lab tests (glucose, occult blood)
- ⚠ Iron overload risk in hemochromatosis patients
Known Interactions
- ● Enhances non-heme iron absorption (beneficial or harmful depending on iron status)
- ● High doses may reduce effectiveness of certain chemotherapy agents
- ● May interfere with anticoagulant therapy (warfarin) at high doses
- ● Aluminum-containing antacids (increased aluminum absorption)
Tolerable upper intake: 2,000 mg/day
Always consult your healthcare provider before starting any supplement.
Frequently Asked Questions
Does Vitamin C help with Upper Respiratory Tract Infections?
How much Vitamin C should I take for Upper Respiratory Tract Infections?
Are there side effects of Vitamin C?
How strong is the evidence for Vitamin C and Upper Respiratory Tract Infections?
Related Evidence
Other ingredients for Upper Respiratory Tract Infections
Vitamin C for other conditions
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. The products and information on this website are not intended to diagnose, treat, cure, or prevent any disease. The evidence grades presented are based on our analysis of published peer-reviewed research and do not constitute medical advice. Always consult your healthcare provider before starting any supplement regimen.