We use essential cookies (authentication, your saved goals/stack) by default. With your permission we’ll also enable privacy-respecting analytics (Vercel Web Analytics, anonymous load-time metrics) and error-replay diagnostics (Sentry — DOM snapshots only when an error fires) so we can fix bugs faster. Learn more about cookies
A7.0
Vitamin A Research
Probably helps
566 peer-reviewed studies
What the evidence says
Mixed evidence
Studies are split: Vitamin A helped in 8 of 17 cases, with the rest inconclusive or showing no benefit.
Most evidence is from high-quality meta-analyses and randomised trials published 1976–2026 with a typical study size of 773 participants.
Based on 566 studies · 81 meta-analyses · 445 RCTs · 768,225 total participants
Confidence
High confidence
What the studies found
8helped5unclear4didn't help· 549 more without graded effect data
By outcome
Therapeutic & clinical
Mixed evidence542 studies
Women's health
Mixed evidence67 studies
Vision & xerophthalmiaCritical for rhodopsin synthesis and night vision; deficiency causes blindness · 2-4 weeks
Limited support64 studies
Anemia & hematology
Probably helps26 studies
Safety profile & toxicity
Mostly mechanism / observational19 studies
Immune supportEnhanced immune cell function and barrier integrity · 2-4 weeks
Mostly mechanism / observational16 studies
Skin healthEssential for skin cell turnover and barrier function · 4-8 weeks
Mostly mechanism / observational7 studies
Heart & blood pressure
Mostly mechanism / observational4 studies
Bone health
Mostly mechanism / observational4 studies
Inflammation
Mostly mechanism / observational3 studies
Cholesterol & lipids
Too few graded studies1 study
Glucose & metabolic
Too few graded studies1 study
Cognitive function
Too few graded studies1 study
By the numbers
Pulled from 37 studies with measurable effects
Likely real effects
70%
across studies
People studied
768k
typical study: 773 people
Strongest designs
526
81 pooled, 445 randomised
Showed benefit
47%
8/17 studies
How long studies ran
Under a week
1
1–3 months
1
3+ months
1
Populations Studied
General population6
Adults and children1
Adults1
HIV-positive women not on antiretroviral drugs1
Steady research
64 studies in the last 5 years · Latest meta-analysis: 2026
197620012026
1Meta-AnalysisCited 5×n=10,495 · very large study2025
D-mannose, triple therapy, vaccine, probiotics, and cranberry serve as potential nonantibiotic intervention options for clinical UTI prevention.
Han Z et al. · Infection (2025)
Nearly 80% of the RCTs utilized double-blind or triple-blind designs.
D-mannose, triple therapy, vaccine, probiotics, and cranberry serve as potential nonantibiotic intervention options for clinical UTI prevention.
2MortalityMeta-AnalysisCited 3×n=672 · large study2024
Based on moderate certainty of evidence, vitamin A had no effect on mortality in the individually randomised trials.
Bjelakovic G et al. · BMJ open (2024)
No clear effect
← WorseNo effectBetter →
Could be chance
Vitamin A did not reduce mortality in individually randomised trials (RR 0.99, 95% CI 0.93 to 1.05; I²=32%; p=0.19; 105 trials; moderate certainty), and this effect was not affected by the risk of bias.
In individually randomised trials, vitamin A had no effect on mortality in children (RR 0.96, 95% CI 0.88 to 1.04; I²=24%; p=0.28; 78 trials, 178 094 participants) nor in adults (RR 1.04, 95% CI 0.97 to 1.13; I²=24%; p=0.27; 27 trials, 61 880 participants).
Vitamin A reduced mortality in the cluster randomised trials (0.84, 95% CI 0.76 to 0.93; I²=66%; p=0.0008; 15 trials, 14 in children and 1 in adults; 364 343 participants; very low certainty).
3Inflammatory biomarkersMeta-AnalysisCited 21×n=1,834 · large study2022
The result of this study demonstrates that supplementation of vitamin A at low and high dosages for short and long durations increases the CRP plasma concentrations on adults and vitamin A supplementation decreases the TNF-α concentrations in chronic hepatitis B on adults.
Gholizadeh M et al. · Scientific Reports (2022)
Among 13,219 articles, 13 studies were included for analysis of CRP and TNF-α, and 9 studies were included for IL-6.
Vitamin A supplementation significantly increased CRP concentration (WMD: 0.84 mg/L; 95% CI 0.29-1.39).
Subgroup analysis showed a negative significant association between 50,000 IU/day retinyl palmitate and IL-6, and between vitamin A and TNF-α in chronic hepatitis B.
4Meta-AnalysisCited 158×n=451,723 · very large study2020
In addition, they further contribute to the ongoing discourse of choosing antenatal MMN over IFA as the standard of care in LMICs.
Oh C et al. · Nutrients (2020)
IFA supplementation showed notable improvement in maternal anemia and the reduction in low birthweight, whereas LNS supplementation had no apparent effect on outcomes; further research that compares LNS and MMN supplementation could help understand differences with these commodities.
For single micronutrient supplementation, improvements were noted in only a few outcomes, mainly pre-eclampsia/eclampsia (calcium), maternal anemia (iron), preterm births (vitamin D), and maternal serum zinc concentration (zinc).
These findings highlight that micronutrient-specific supplementation should be tailored to specific groups or needs for maximum benefit.
5Mother-to-child HIV transmissionMeta-AnalysisCited 11×n=6,601 · very large study2017
Antepartum or postpartum vitamin A supplementation, or both, probably has little or no effect on mother-to-child transmission of HIV in women living with HIV infection and not on antiretroviral drugs.
Wiysonge CS et al. · The Cochrane database of systematic reviews (2017)
Antepartum or postpartum vitamin A supplementation, or both, probably has little or no effect on mother-to-child transmission of HIV in women living with HIV infection and not on antiretroviral drugs.
The intervention has largely been superseded by ART which is widely available and effective in preventing vertical transmission.
6Maternal and infant mortality and morbidityMeta-AnalysisCited 26×n=8,577 · very large study2016
There was no evidence of benefit from different doses of vitamin A supplementation for postpartum women on maternal and infant mortality and morbidity, compared with other doses or placebo.
Oliveira JM et al. · The Cochrane database of systematic reviews (2016)
No clear effect
← WorseNo effectBetter →
Effects were less certain at six months (risk ratio (RR) 0.50, 95% CI 0.09 to 2.71; 564 participants; 1 RCT; low-quality evidence).
We found insufficient evidence that vitamin A increases abdominal pain (RR 1.28, 95% CI 0.95 to 1.73; 786 participants; 1 RCT; low-quality evidence).
We found low-quality evidence that vitamin A supplementation increased breast milk retinol concentrations by 0.20 µmol/L at three to three and a half months (mean difference (MD) 0.20 µmol/L, 95% CI 0.08 to 0.31; 837 participants; 6 RCTs).
7Miscarriage preventionMeta-AnalysisCited 60×n=276,820 · very large study2016
Taking any vitamin supplements prior to pregnancy or in early pregnancy does not prevent women experiencing miscarriage.
Balogun OO et al. · The Cochrane database of systematic reviews (2016)
Barely noticeable benefit
← WorseNo effectBetter →
Multivitamin supplementation There was evidence of a decrease in the risk for stillbirth among women receiving multivitamins plus iron and folic acid compared iron and folate only groups (RR 0.92, 95% CI 0.85 to 0.99, 10 trials, 79,851 women; high-quality evidence).
Antioxidant vitamins supplementation There was no evidence of differences in early or late miscarriage between women given antioxidant compared with the low antioxidant group (RR 1.12, 95% CI 0.24 to 5.29, one trial, 110 women).
Taking any vitamin supplements prior to pregnancy or in early pregnancy does not prevent women experiencing miscarriage.
8Iron deficiencyMeta-AnalysisCited 11×n=443 · medium study2024
Overnutrition is associated with increased risk of ID, but not zinc or VA deficiencies, with an inverted U-shaped relationship observed between iron status and bodyweight.
Tan X et al. · BMJ global health (2024)
Huge harm
← WorseNo effectBetter →
Likely real
Synthesising 16 records of OR from seven eligible studies, overnutrition (overweight and obesity) increased odds of iron deficiency (ID) (OR (95% CI): 1.51 (1.20 to 1.82), p<0.0001, I2=40.7%).
Odds appeared to be higher for children living with obesity (1.88 (1.33 to 2.43), p<0.0001, I2=20.6%) in comparison to those with overweight (1.31 (0.98 to 1.64), p<0.0001, I2=40.5%), although between group differences were not significant (p=0.08).
Overnutrition is associated with increased risk of ID, but not zinc or VA deficiencies, with an inverted U-shaped relationship observed between iron status and bodyweight.
9Subclinical vitamin A deficiencySystematic ReviewCited 47×n=4,455 · very large study2019
Fortifying staple foods with vitamin A alone may make little or no difference to serum retinol concentrations or the risk of subclinical vitamin A deficiency.
Hombali AS et al. · The Cochrane database of systematic reviews (2019)
No clear effect
← WorseNo effectBetter →
It is uncertain whether vitamin A alone reduces the risk of subclinical vitamin A deficiency (risk ratio (RR) 0.45, 95% CI 0.19 to 1.05; 2 studies; 993 participants; I² = 33%, very low-certainty evidence).
The certainty of the evidence was mainly affected by risk of bias, imprecision and inconsistency.It is uncertain whether vitamin A fortification reduces clinical vitamin A deficiency, defined as night blindness (RR 0.11, 95% CI 0.01 to 1.98; 1 study, 581 participants, very low-certainty evidence).
When compared to no intervention, it is uncertain whether the intervention reduces the risk of subclinical vitamin A deficiency (RR 0.71, 95% CI 0.52 to 0.98; 2 studies; 318 participants; I² = 0%; very low-certainty evidence) .