Improvement after a supplement is not the same as a comparative result
Start with the comparison. A before-and-after change alone cannot isolate the contribution of an ingredient.
Vitamin C
Selected research topic
Immune and respiratory health
Some measured outcomes improved in human comparison studies. Read these findings with their populations and conditions.
Some findings concern patients or people with a deficiency.
- Publications for this topic
- 10
- Human comparison publications
- 1
- Publications needing review
- 8
Findings in the studies
infections caused by respiratory viruses
Human comparison research
- A better result than the comparison group was reported.Patient group · Single ingredient
Measurement and study conditions
- Study type
- Review
- Study population
- Human participants · Patient group
- Ingredients tested
- Single ingredient
- How results were compared
- Results were compared between groups. · Study comparison: review summary of placebo-controlled trials; reports shorter respiratory viral infections without a
- Measurement time
- Not confirmed.
Research with unclear study subject or type
- A change was reported, but the comparison could not be confirmed.Single ingredient
Measurement and study conditions
- Study type
- Review
- Study population
- Recorded population category: General population. Whether the research involved humans needs confirmation.
- Ingredients tested
- Single ingredient
- Additional measurement information
- Secondary outcome
- Measurement time
- Not confirmed.
duration of mild symptoms
Research with unclear study subject or type
- No clear difference in this measurement was found between the compared groups.Single ingredient
Measurement and study conditions
- Study type
- Meta-analysis
- Study population
- Recorded population category: General population. Whether the research involved humans needs confirmation.
- Ingredients tested
- Single ingredient
- How results were compared
- Results were compared between groups. · Study comparison: vitamin C vs placebo in five comparisons; mild-symptom duration
- Additional measurement information
- Secondary outcome
- Measurement time
- Not confirmed.
duration of severe symptoms
Research with unclear study subject or type
- The study reported improvement in this measurement.Single ingredient
Measurement and study conditions
- Study type
- Meta-analysis
- Study population
- Recorded population category: General population. Whether the research involved humans needs confirmation.
- Ingredients tested
- Single ingredient
- How results were compared
- Results were compared between groups. · Study comparison: vitamin C vs placebo in five comparisons; severe-symptom duration
- Additional measurement information
- Secondary outcome
- Measurement time
- Not confirmed.
function of the human immune system
Research with unclear study subject or type
- A change was reported, but the comparison could not be confirmed.Single ingredient
Measurement and study conditions
- Study type
- Review
- Study population
- Recorded population category: General population. Whether the research involved humans needs confirmation.
- Ingredients tested
- Single ingredient
- How results were compared
- Study comparison: review-level supplementation claim about immune-function measures
- Additional measurement information
- Biomarker
- Measurement time
- Not confirmed.
Other measured outcomes (1)
severity of the common cold
Research with unclear study subject or type
- The study reported improvement in this measurement.Single ingredient
Measurement and study conditions
- Study type
- Meta-analysis
- Study population
- Recorded population category: General population. Whether the research involved humans needs confirmation.
- Ingredients tested
- Single ingredient
- How results were compared
- Results were compared between groups. · Study comparison: vitamin C vs placebo; pooled common-cold severity
- Additional measurement information
- Secondary outcome
- Measurement time
- Not confirmed.
This result is held for interpretation. That does not mean research found no effect.
Outcome groups needing additional review (3)
- duration of common cold symptoms · Distinct papers needing additional review: 1Direction unclear: 1
- immune parameters · Distinct papers needing additional review: 1Evidence criteria check: 1
- pneumonia incidence · Distinct papers needing additional review: 1Direction unclear: 1
One paper can appear under multiple measured outcomes or review reasons, so these counts should not be added together.
Representative outcome and study details
Studies with an unspecified organism reported no clear between-group difference in duration of mild symptoms.
Single-ingredient studies · between-group comparison
1 publications linked to this result
- Route, form, dose, or population details are incomplete, so the findings cannot be confirmed as directly comparable.
Data coverage and detailed study classifications
Paper counts are separated by research topic below. One paper may contribute to multiple findings.
Analysis status: Public-ready
Ingredient analysis date:
How the grade was determined: C
The 50.0 evidence score includes 1 independent human studies and 1 clinical studies in the representative benefit area. The C tier remains conservative because of limited repetition across independent human clinical studies, too few clinical findings with an explicit effect direction.
The grade is based mainly on the research area with the most evidence. It does not mean the same result was found in other areas.
Papers linked to this ingredient overall: 106
Papers linked to this topic 10 · distinct papers 10 · papers with a confirmed human comparison 1 · papers needing additional review 8
A publication may appear in more than one count. These numbers should not be added. Ingredient-wide papers, topic-linked papers, and sources in outcome groups use different scopes. Adding source counts may count the same paper more than once.
- duration of common cold symptoms: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- duration of mild symptoms: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- duration of severe symptoms: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- function of the human immune system: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- immune parameters: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- infections caused by respiratory viruses: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 1
- pneumonia incidence: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- severity of the common cold: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
What the research found
duration of mild symptoms
No clear difference in this measurement was found between the compared groups.
Meta-analysis · Single ingredient · General population
Between-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
duration of severe symptoms
The study reported improvement in this measurement.
Meta-analysis · Single ingredient · General population
Between-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
infections caused by respiratory viruses
The study reported improvement in this measurement.
Review · Single ingredient · Patient group
Between-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
severity of the common cold
The study reported improvement in this measurement.
Meta-analysis · Single ingredient · General population
Between-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
function of the human immune system
A change was reported, but the comparison could not be confirmed.
Review · Single ingredient · General population
Analysis coverage and paper counts
1 paper · 1 measured outcome
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
infections caused by respiratory viruses
A change was reported, but the comparison could not be confirmed.
Review · Single ingredient · General population
Analysis coverage and paper counts
1 paper · 1 measured outcome
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
duration of common cold symptoms
The study needs further checking before its result can be interpreted.
Review · Single ingredient · General population
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
immune parameters
The study needs further checking before its result can be interpreted.
Review · Ingredient combination · General population
Several ingredients were used together. This does not establish the effect of this ingredient alone or synergy.
Between-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
pneumonia incidence
The study needs further checking before its result can be interpreted.
Review · Single ingredient · Patient group
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
Unspecified measured outcome
The study needs further checking before its result can be interpreted.
Controlled study in people · Single ingredient · Unspecified population
Between-group comparison
Analysis coverage and paper counts
2 papers · 2 measured outcomes
2 papers held from direction counts
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
Unspecified measured outcome
The study needs further checking before its result can be interpreted.
Meta-analysis · Single ingredient · Patient group
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
Unspecified measured outcome
The study needs further checking before its result can be interpreted.
Other evidence · Unknown intervention · Unspecified population
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
Unspecified measured outcome
The study needs further checking before its result can be interpreted.
Review · Unknown intervention · Unspecified population
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
1 papers held from direction counts
Review overlap with primary papers is unknown; counts stay separate.
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
How to read research findings
How should I read research findings?
Research guidesNo clear difference and an uninterpretable result are different
A reported null comparison contains a result. An abstract without an interpretable comparison leaves a question unresolved.
Paper counts and study counts are different
Count original research separately from research that reanalyzes it. Publication volume is neither replication nor a quality rating.
Side effects and combination findings
Findings from this ingredient alone are shown separately from those involving another supplement or medication.
No combination cautions are available to show in the current data. This does not guarantee safety.
Review 1 combination findings and 0 findings that outperformed an ingredient alone.
Reported improvements with combinations
Combination findings are grouped by how the study compared them. This is not a recommendation to combine ingredients.
Combinations with reported improvement
The combination showed improvement, but each ingredient's contribution is unclear.
비타민 EIn a triple-blind RCT of 60 women with endometriosis, daily supplementation with 1000 mg Vitamin C and 800 IU Vitamin E for 8 weeks significantly reduced pelvic pain, dysmenorrhea, and dyspareunia (p < 0.001) compared to placebo.