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Smoking status: not checked. Vitamin A: what these mean for you changes depending on whether you smoke or used to, and you have not told us. That check was skipped.
Head-to-head evidence comparison — which supplement is right for you?
Vitamin A vs Vitamin K2: Vitamin A has the stronger overall evidence (7 vs 5/10); they work on different things and are often used together, not either/or. Take the 60-second quiz for a pick tailored to your goals.
Vitamin A wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Limited support
2 of 9 studies with measurable effects showed benefit.
Top outcomes
Verdict
Probably helps
3 of 5 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (2)
Outcomes where both Vitamin A and Vitamin K2 have evidence — compare verdict strength side-by-side.
2500-5000 IU daily (retinol); up to 25000 IU (beta-carotene). These are typical label doses, not doses used in the cited trials. The one cited paper is in preterm infants, not adults.
With fat-containing meal, Any time of day
Mixed carotenoids or low-dose retinyl palmitate
100-200mcg (MK-7)
With a meal containing fat
MK-7 (menaquinone-7)
and 2 more not shown
No established clinically beneficial or harmful interaction.
No change needed. Take either with a meal that contains fat.
2-4 weeks
2-4 weeks
4-8 weeks
With chronic excess
4-12 weeks
1-3 years
1-3 years
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=1671672
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=7298
Five trials in Malawi, South Africa, Tanzania and Zimbabwe, none of whose participants received antiretroviral therapy. Four trials had 6995 women and one had 303.
Vitamins K2 and D3 Improve Long COVID, Fungal Translocation, and Inflammation: Randomized Controlled Trial
Nutrients (2025) · Rct · n=151
The median age was 46 years; 71% were female and 29% were non-white.
The effect of vitamin K2 supplementation on bone turnover biochemical markers in postmenopausal osteoporosis patients: a systematic review and meta-analysis
Frontiers in endocrinology (2025) · Meta analysis · n=2570
Vitamin K2 (VK2) increased osteocalcin (OC; MD 1.86, 95% CI 1.17-2.56) and bone-specific alkaline phosphatase (BAP; MD 1.49, 95% CI 0.98-2.00).
Vitamin K2 in Managing Nocturnal Leg Cramps: A Randomized Clinical Trial
JAMA internal medicine (2024) · Rct · n=199
Of the 199 enrolled individuals, 108 (54.3%) were female, and the mean (SD) age was 72.3 (5.5) years.
In a 1-year randomised trial of 311 Chinese men and postmenopausal women, 90 μg of MK-7 a day slowed femoral neck bone loss in the postmenopausal women and 50 μg did not, with no effect in men (PMID 32060566). In a 3-year randomised placebo-controlled trial of 244 healthy postmenopausal women, 180 μg a day reduced the decline in bone density at the lumbar spine and femoral neck but not the total hip (PMID 23525894). In a 3-year randomised placebo-controlled trial of 142 postmenopausal women with osteopenia, 375 μg a day with calcium and vitamin D did not change bone density at any site (PMID 33030563). The curve stays flat above 90 μg because no trial compared 90 μg with a higher dose, and the 375 μg trial found no effect. The cited BMD meta-analyses do not state a dose and mostly pool menaquinone-4 trials, so they are not plotted.
AI-estimated from published studies. Interpret as directional guidance.
Vitamin A has a higher evidence score (7/10 vs 5/10) and wins in 2 of 3 categories.
No established clinically beneficial or harmful interaction. No change needed. Take either with a meal that contains fat. Consult a healthcare provider for personalized advice.
Commonly recommended vs ask-your-clinician vs avoid — a general, safety-first overview.
Which supplements clash with blood thinners, thyroid meds, antibiotics & more — and what to do.
Hot flashes, bone, sleep, muscle — the basics that hold up vs the phytoestrogen hype.
Worth it if you’re deficient (and many are) — dosing, testing, D3 vs D2, and the K2 question.
The right pick depends on your goals. Answer a few quick questions for a personalised recommendation — or dig into the full evidence on each.