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Head-to-head evidence comparison — which supplement is right for you?
Selenium vs Vitamin B12: Vitamin B12 has the stronger overall evidence (7.5 vs 6.5/10); they're alternatives for prenatal support — the best pick depends on your goals. Take the 60-second quiz for a pick tailored to your goals.
Vitamin B12 wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Likely helps
19 of 26 studies with measurable effects showed benefit.
Top outcomes
Verdict
Likely helps
12 of 17 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (1)
Outcomes where both Selenium and Vitamin B12 have evidence — compare verdict strength side-by-side.
100-200mcg
With food
Selenomethionine (best absorbed)
500-1000mcg daily for maintenance; higher for deficiency
Morning (may be energizing), With or without food
Methylcobalamin (sublingual)
4-8 weeks
4-8 weeks
2-4 weeks
4-8 weeks
Weeks to months
Selenium, antioxidants, cardiovascular disease, and all-cause mortality: a systematic review and meta-analysis of randomized controlled trials
The American journal of clinical nutrition (2020) · Meta analysis · n=9423
However, a decreased risk with antioxidant mixtures was seen for CVD mortality when selenium was part of the mix (RR: 0.77; 95% CI: 0.62, 0.97; P = 0.02), with no association when selenium was absent.
Selenium for preventing cancer
The Cochrane database of systematic reviews (2018) · Meta analysis · n=27232
For analyses of RCTs with low risk of bias, the summary risk ratio (RR) for any cancer incidence was 1.01 (95% confidence interval (CI) 0.93 to 1.10; 3 studies, 19,475 participants; high-certainty evidence).
Selenium and prostate cancer: systematic review and meta-analysis
The American journal of clinical nutrition (2012) · Meta analysis · n=13254
Three high-quality studies included in the meta-analysis of toenail selenium and cancer risk indicated a reduction in prostate cancer risk (estimated RR: 0.29; 95% CI: 0.14, 0.61) with a toenail selenium concentration between 0.85 and 0.94 μg/g.
Efficacy of different routes of vitamin B12 supplementation for the treatment of patients with vitamin B12 deficiency: A systematic review and network meta-analysis
Irish journal of medical science (2024) · Meta analysis · n=4275
Regarding the hemoglobin level, the pooled effect sizes showed no difference between all routes of administration that could reach statistical significance.
Dosage exploration of combined B-vitamin supplementation in stroke prevention: a meta-analysis and systematic review
The American journal of clinical nutrition (2024) · Meta analysis · n=76664
In areas without and with partial folic acid fortification, combined B-vitamin supplementation significantly reduced the risk of stroke by 34% [RR: 0.66; 95% confidence interval (CI): 0.50, 0.86] and 11% (RR: 0.89; 95% CI: 0.79, 1.00), respectively.
Vitamin Status in Patients with Phenylketonuria: A Systematic Review and Meta-Analysis
International journal of molecular sciences (2024) · Meta analysis · n=770
The effect sizes were expressed as standardised mean differences.
Based on Cochrane systematic review showing moderate-certainty evidence for TPO antibody reduction. Effects on thyroid hormone levels (TSH, T4, T3) were inconsistent across studies.
AI-estimated from published studies. Interpret as directional guidance.
Vitamin B12 has a higher evidence score (7.5/10 vs 6.5/10) and wins in 2 of 3 categories.
For prenatal support, Vitamin B12 has a higher relevance score (85 vs 72).
No known interactions between Selenium and Vitamin B12 have been documented in our database. However, always consult a healthcare provider before combining supplements.
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The right pick depends on your goals. Answer a few quick questions for a personalised recommendation — or dig into the full evidence on each.