Vitamin C for Upper Respiratory Tract Infections
B Good Evidence At least one randomized trial supports this, with mostly consistent results.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.
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B
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
Review
UCI Sports Nutrition Project: The Role of Nutrition in the Prevention and Management of Illnesses …
Dose: None
vs: None
Outcome: None
Effect: None
None
Population: Elite/professional cyclists nutrition review
Review
Micronutrient Deficiencies in Pediatric IBD: How Often, Why, and What to Do?
Dose: None
vs: None
Outcome: Micronutrient deficiency management in pediatric IBD
Effect: None
None
Population: Children with inflammatory bowel disease (review)
Other
Circulating micronutrient levels and respiratory infection susceptibility and severity: a bidirectional Mendelian randomization analysis.
Dose: 12 circulating micronutrients
vs: Genetic instrument comparison
Outcome: URTI, LRTI, pneumonia risk
Effect: None
None
Population: Large genetic cohort (MR analysis)
Review
Nutraceuticals and pharmacological to balance the transitional microbiome to extend immunity during COVID-19 and other …
Dose: Probiotics, nutraceuticals
vs: None
Outcome: Immune response modulation in COVID-19
Effect: None
None
Population: COVID-19 patients with gut dysbiosis
Randomized Controlled Trial
Zinc and L-Ascorbic Acid Dietary Supplementation Affected Antioxidant Status, Heat Shock Protein 70, and Some …
Dose: None
vs: Basal diet without supplementation
Outcome: Antioxidant status, hematology, growth in broilers
Effect: None
None
Population: Broiler chickens
Randomized Controlled Trial
n=171
24 weeks
Double-blind
Probiotics with vitamin C for the prevention of upper respiratory tract symptoms in children aged …
Dose: 12.5 billion cfu/d
vs: placebo
Outcome: None
Effect: or 6
P=0.0300
Population: None
Key Statistics
30
Studies
10000
Participants
↑
Positive
B
Grade
Referenced Papers
Nutrients
2025
4 citations
International journal of …
2025
2 citations
Journal of translational …
2024
2 citations
Frontiers in nutrition
2024
1 citations
Biological trace element …
2022
5 citations
Beneficial microbes
2021
18 citations
European journal of …
2021
Nutrients
2020
75 citations
Efficacy of vitamin C for the prevention and treatment of upper respiratory tract infection. A meta-analysis in children.
Meta-Analysis
European journal of …
2019
54 citations
Journal of evidence-based …
2017
134 citations
European journal of …
2017
18 citations
Zhongguo Zhong yao …
2017
European journal of …
2015
70 citations
World journal of …
2015
62 citations
Zhongguo Zhong yao …
2014
4 citations
Zhongguo Zhong yao …
2013
European journal of …
2012
225 citations
The British journal …
2012
40 citations
American family physician
2012
Journal of the …
2011
8 citations
International journal of …
2008
11 citations
American journal of …
2006
51 citations
Clinical evidence
2003
Clinical evidence
2003
The British journal …
2002
358 citations
Primary care
2002
56 citations
American family physician
2002
Canadian journal of …
2001
72 citations
Medicine and science …
2000
262 citations
Medicine and science …
2000
248 citations
Alternative medicine review …
2000
Canadian journal of …
1998
41 citations
Journal of applied …
1997
434 citations
International journal of …
1997
167 citations
Exercise immunology review
1997
27 citations
Respiration; international review …
1989
25 citations
Scandinavian journal of …
1977
56 citations
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?
Based on 30 studies with 10,000 participants, there is moderate evidence from clinical studies that Vitamin C may support Upper Respiratory Tract Infections management. Our evidence grade is B (Good Evidence).
How much Vitamin C should I take for Upper Respiratory Tract Infections?
Studies have used various dosages. A commonly studied range is 75-90 mg/day. Always consult your healthcare provider before starting any supplement regimen.
Are there side effects of Vitamin C?
Reported side effects may include 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. Most side effects are mild and dose-dependent. Consult your doctor if you experience any adverse reactions.
How strong is the evidence for Vitamin C and Upper Respiratory Tract Infections?
We rate the evidence as Grade B (Good Evidence). This rating is based on 30 peer-reviewed studies with 10,000 total participants. The overall direction of effect is positive.
Related Evidence
Other ingredients for Upper Respiratory Tract Infections
Vitamin C for other conditions
References
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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.