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A9.0
Vitamin A Research
Mixed evidenceModerate safety
46 peer-reviewed studies
What the evidence says
Mixed evidence
Studies are split: Vitamin A helped in 7 of 16 cases, with the rest inconclusive or showing no benefit.
Most evidence is from high-quality meta-analyses and randomised trials published 2016–2026 with a typical study size of 773 participants.
Based on 46 studies · 22 meta-analyses · 7 RCTs · 768,119 total participants
Confidence
High
What the studies found
7helped5unclear4didn't help· 30 more without graded effect data
By outcome
Therapeutic & clinical
Mixed evidence33 studies
Vision & xerophthalmiaCritical for rhodopsin synthesis and night vision; deficiency causes blindness · 2-4 weeks
Limited support8 studies
Women's health
Mixed evidence6 studies
Anemia & hematology
Probably helps5 studies
Immune supportEnhanced immune cell function and barrier integrity · 2-4 weeks
Mostly mechanism / observational3 studies
Skin healthEssential for skin cell turnover and barrier function · 4-8 weeks
Mostly mechanism / observational3 studies
Heart & blood pressure
Mostly mechanism / observational3 studies
Inflammation
Mostly mechanism / observational3 studies
Cholesterol & lipids
Too few graded studies1 study
Glucose & metabolic
Too few graded studies1 study
Bone health
Too few graded studies1 study
By the numbers
Pulled from 35 studies with measurable effects
Likely real effects
67%
across studies
People studied
768k
typical study: 773 people
Strongest designs
29
22 pooled, 7 randomised
Showed benefit
44%
7/16 studies
How long studies ran
Under a week
1
1–3 months
1
3+ months
1
Populations Studied
General population5
Adults and children1
Adults1
HIV-positive women not on antiretroviral drugs1
Active research area
34 studies in the last 5 years · Latest meta-analysis: 2026
201620212026
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).
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) .
This meta-analysis indicated that people with tuberculosis exhibited low levels of vitamins A and D, while vitamin D deficiency was identified as a risk factor for tuberculosis.
Zhou Y et al. · Annals of medicine (2024)
Huge harm
← WorseNo effectBetter →
Likely real
The random-effect model showed that people with tuberculosis may exhibit vitamin A deficiency (OR = 10.66, 95%CI: 2.61-43.63, p = .001), while limited cohort studies showed that vitamin A supplementation may reduce tuberculosis occurrence.
Additionally, vitamin D deficiency was identified as a risk factor for tuberculosis development (RR = 1.69, 95%CI: 1.06-2.67, p = .026), and people with tuberculosis generally had lower vitamin D levels (OR = 2.19, 95%CI: 1.76-2.73, p < .001) compared to other groups.
This meta-analysis indicated that people with tuberculosis exhibited low levels of vitamins A and D, while vitamin D deficiency was identified as a risk factor for tuberculosis.
13Stroke preventionMeta-AnalysisCited 6×n=17 · very small study2024
Our study has established noteworthy connections between vitamin A, vitamin B-complex, vitamin B6, folate, vitamin C, and vitamin D in the realm of stroke prevention.
Tripathi S et al. · European journal of clinical investigation (2024)
Our study has established noteworthy connections between vitamin A, vitamin B-complex, vitamin B6, folate, vitamin C, and vitamin D in the realm of stroke prevention.
These findings add substantial weight to the accumulating evidence supporting the potential advantages of vitamin interventions in mitigating the risk of stroke.
However, to solidify and validate these observations, additional research is imperative.
Until more information is available, it is advisable to consume vitamin A primarily from plant sources, avoid excessive consumption from dietary supplements and animal sources, and lower consumption from fortified foods.2021.
Knapik JJ et al. · Journal of special operations medicine : a peer reviewed journal for SOF medical professionals (2021)
Several lines of evidence suggest that excessive dietary intake of vitamin A might be associated with an increased risk of bone fractures.
Meta-analysis of observational human studies that have examined vitamin A and fractures suggests that dietary consumption of large amounts of vitamin A in the form of ß-carotene likely has a protective effect, reducing the risk of fractures.
On the other hand, meta-analyses that have specifically examined hip fractures have shown that total vitamin A (all types) or retinol consumption may increase the risk of hip fractures.
High intake of total vitamin A or retinol increased hip fracture risk, while high intake of some carotenoids reduced hip fracture risk.2021.
Knapik JJ et al. · Journal of special operations medicine : a peer reviewed journal for SOF medical professionals (2021)
Large harm
← WorseNo effectBetter →
Meta-analyses indicated that risk of hip fracture was increased by high dietary intake of total vitamin A (RR = 1.29; 95% CI = 1.07-1.57) or retinol (RR = 1.23; 95% CI = 1.02-1.48).
Hip fracture risk was reduced by high dietary intake of total carotene (RR = 0.62; 95% CI = 0.42-0.93), β-carotene (RR = 0.72; 95% CI = 0.58-0.89), or α-carotene (RR = 0.81; 95% CI = 0.67-0.97).
Total fracture risk was not associated with any vitamin A compound.
Therefore, vitamin A supplementation alone may reduce the risk of anemia, by improving hemoglobin and ferritin levels in individuals with low serum retinol levels.
da Cunha MSB et al. · Critical reviews in food science and nutrition (2019)
Large benefit
← WorseNo effectBetter →
The meta-analysis of the clinical trials showed that VAS reduces the risk of anemia by 26% and raises hemoglobin levels, compared to non-treated group, independent of the life stage.
The search yielded 23 eligible studies, 21 clinical trials and 2 cohort studies, with children, teenagers, pregnant or lactating women.
Therefore, vitamin A supplementation alone may reduce the risk of anemia, by improving hemoglobin and ferritin levels in individuals with low serum retinol levels.
19Cytokine levels in autoimmune diseasesMeta-AnalysisCited 7×2019
Vitamin A supplementation effects on gene expression and may improve serum level of cytokines and clinical signs of autoimmune disease but there is no adequate evidence.
Harirchian MH et al. · Clinical nutrition (Edinburgh, Scotland) (2019)
Vitamin A supplementation effects on gene expression and may improve serum level of cytokines and clinical signs of autoimmune disease but there is no adequate evidence.
20Overall survival in breast cancerMeta-AnalysisCited 39×2018
Our findings suggest limited evidence for the significantly inverse association between the prediagnosis dietary intake of β-carotene and OS among women with breast cancer.
He J et al. · Clinical breast cancer (2018)
Our findings suggest limited evidence for the significantly inverse association between the prediagnosis dietary intake of β-carotene and OS among women with breast cancer.
However, the intake of other vitamin A derivatives was not significantly associated with survival.