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Head-to-head evidence comparison — which supplement is right for you?
Vitamin D3 wins 1 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Mixed evidence
8 of 17 studies with measurable effects showed benefit.
Top outcomes
Verdict
Probably helps
15 of 26 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (1)
Outcomes where both Vitamin A and Vitamin D3 have evidence — compare verdict strength side-by-side.
2500-5000 IU daily (retinol); up to 25000 IU (beta-carotene)
With fat-containing meal, Any time of day
Mixed carotenoids or low-dose retinyl palmitate
2000-4000 IU daily
Morning with breakfast
D3 (cholecalciferol) softgel or liquid
Very high vitamin A may interfere with vitamin D signaling
Avoid very high doses of vitamin A (>10,000 IU) with vitamin D therapy.
2-4 weeks
2-4 weeks
4-8 weeks
With chronic excess
4-8 weeks
4-8 weeks
2-4 weeks
4-8 weeks
Effects of primary or secondary prevention with vitamin A supplementation on clinically important outcomes: a systematic review of randomised clinical trials with meta-analysis and trial sequential analysis
BMJ open (2024) · Meta analysis · n=672
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.
Vitamin and Mineral Supplementation During Pregnancy on Maternal, Birth, Child Health and Development Outcomes in Low- and Middle-Income Countries: A Systematic Review and Meta-Analysis
Nutrients (2020) · Meta analysis · n=451723
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.
Vitamin A supplements for reducing mother-to-child HIV transmission
The Cochrane database of systematic reviews (2017) · Meta analysis · n=6601
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.
Vitamin D supplementation vs. placebo and incident type 2 diabetes in an ancillary study of the randomized Vitamin D and Omega-3 Trial
Nature communications (2025) · Meta analysis · n=5205
Mean body mass index (BMI) was 27.5 kg/m2 (SD = 5.3), with 51% female and 17% Black race/ethnicity.
Vitamin D Supplementation for Patients with Dysmenorrhoea: A Meta-Analysis with Trial Sequential Analysis of Randomised Controlled Trials
Nutrients (2024) · Meta analysis · n=687
TSA revealed that the current RCTs provide sufficient information.
Vitamin D and respiratory tract infections
BMJ (2017) · Meta analysis · n=11321
12% reduction in respiratory infections overall
Meta-analysis showed 12% overall reduction in respiratory infections, with greater benefits in severely deficient individuals. Daily dosing more effective than bolus. Conservative estimate assumes most users not severely deficient.
AI-estimated from published studies. Interpret as directional guidance.
Vitamin D3 has a higher evidence score (9/10 vs 9/10) and wins in 1 of 3 categories.
For support immune system, Vitamin D3 has a higher relevance score (92 vs 75).
Very high vitamin A may interfere with vitamin D signaling Avoid very high doses of vitamin A (>10,000 IU) with vitamin D therapy. Consult a healthcare provider for personalized advice.