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 A
Nutrient status
Human studies reported an association with prevalence of deficiency.
Scope not specified · Human studies · Includes deficiency groups · comparator not confirmed
Publications for this result: 1
Other outcomes and study details
Distinct publications linked to this topic: 4
- Route, form, dose, or population details are incomplete, so the findings cannot be confirmed as directly comparable.
What has been studied?
Distinct human comparison papers: 0
prevalence of deficiency
Other human research, including observational studies and reviews
- An association was observed. This does not establish that the ingredient caused the change.Deficiency group · 1991–2013
Measurement and study conditions
- Observational study
- Observational study
- Unknown intervention
- Deficiency group
- Primary outcome
- Comparison unclear
- Timepoint: 1991–2013
- Study comparison: Population prevalence estimates over time and by region; not a supplement trial
This result is held for interpretation. That does not mean research found no effect.
Outcome groups needing additional review (3)
- apparent absorption · Distinct papers needing additional review: 1Evidence criteria check: 1
- prevalence of vitamin A · Distinct papers needing additional review: 1Direction unclear: 1
- vitamin A deficiency · 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.
Research topics to explore
Research topics to explore
Review findings reported in each research area.
Topics with more linked papers appear first.
- View selected result
Nutrient status
Related papers 4 · comparison findings need further review
- View results
Cognition
Related papers 1 · comparison findings need further review
- View results
Glucose and metabolic health
Related papers 1 · comparison findings need further review
- retinol and MetS · Interpretation held
- View results
Immune and respiratory health
Related papers 1 · human comparison papers 1
- prevalence of lifetime or current asthma · No clear difference between groups
- View results
Women's health
Related papers 1 · comparison findings need further review
Data coverage and detailed study classifications
Paper counts are separated by research topic below. One paper may contribute to multiple findings.
Analysis status: Limited data
Ingredient analysis date:
How the grade was determined: C
The 27.6 evidence score includes 0 independent human studies and 0 clinical studies in the representative benefit area. The C tier remains conservative because of the evidence centers on contextual or measured outcomes rather than general-use effects, limited repetition across independent human clinical studies.
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: 63
Papers linked to this topic 4 · distinct papers 4 · comparison findings need further review · papers needing additional review 3
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.
- apparent absorption: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- prevalence of deficiency: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- prevalence of vitamin A: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
- vitamin A deficiency: Sources represented in this measurement group: 1 · Distinct papers with human comparisons for this outcome: 0
Nutrient status
What the research found
prevalence of deficiency
An association was observed. This does not establish that the ingredient caused the change.
Observational study · Unknown intervention · Deficiency group
The comparison could not be confirmed.
Analysis coverage and paper counts
1 paper · 1 measured outcome
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
apparent absorption
The study needs further checking before its result can be interpreted.
Other evidence · Single ingredient · General population
Within-group comparison
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.
prevalence of vitamin A
The study needs further checking before its result can be interpreted.
Review · Unknown intervention · 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.
vitamin A deficiency
The study needs further checking before its result can be interpreted.
Meta-analysis · Unknown intervention · 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.
Cognition
What the research found
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.
Glucose and metabolic health
What the research found
retinol and MetS
The study needs further checking before its result can be interpreted.
Meta-analysis · Unknown intervention · 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 and respiratory health
What the research found
prevalence of lifetime or current asthma
No clear difference in this measurement was found between the compared groups.
Other evidence · Single ingredient · General population
Between-group comparison
Analysis coverage and paper counts
1 paper · 1 measured outcome
Direction counts are distinct papers within each row. Outcome contributions count endpoint results, so one paper may contribute more than once.
Women's health
What the research found
Unspecified measured outcome
The study needs further checking before its result can be interpreted.
Controlled study in people · Ingredient combination · Patient group
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
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.
Caution findings
1
Findings from individual and combined use, plus reviewed cautions
Key precautions
No reviewed caution rules are available yet. Reported caution findings are shown below.
These findings were reported in studies. They do not predict an individual's experience.
Findings to review with care
Side effects reported for the ingredient alone are separated from findings involving another supplement or medication.
Side effects reported with this ingredient alone
Symptoms or adverse events reported in studies without another active ingredient.
Teratogenic effects1 papers
Excessive vitamin A intake during early pregnancy may cause teratogenic effects.Human studies · Systematic review