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Head-to-head evidence comparison — which supplement is right for you?
Vitamin C wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Likely helps
27 of 34 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 C have evidence — compare verdict strength side-by-side.
100-200mcg
With food
Selenomethionine (best absorbed)
500-1000mg
With meals, Split doses if taking >500mg
Ascorbic acid or buffered vitamin C
4-8 weeks
4-8 weeks
Ongoing
1-2 weeks
4-8 weeks
With high doses (>2g)
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.
Vitamin C supplementation for prevention and treatment of pneumonia
The Cochrane database of systematic reviews (2020) · Meta analysis · n=2774
We are uncertain of the effect of vitamin C supplementation on mortality due to pneumonia (RR 0.21, 95% CI 0.03 to 1.66; 1 study, 57 participants; very low-quality evidence).
Vitamin C supplementation in pregnancy
The Cochrane database of systematic reviews (2015) · Meta analysis · n=20038
Conversely, the risk of term PROM was increased when supplementation included vitamin C and vitamin E (average RR 1.73, 95% CI 1.34 to 2.23; 3060 participants; two studies; I² = 0%).
Enhanced Vitamin C Delivery: A Systematic Literature Review Assessing the Efficacy and Safety of Alternative Supplement Forms in Healthy Adults
Nutrients (2025) · Systematic review
Most studies (77%) had a low risk of bias.
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.
Based on 3 meta-analyses of sepsis patients. One study showed RR 0.60 for mortality reduction, but another showed increased risk (RR 1.21). Evidence quality rated as low to very low. Effect limited to intravenous administration in critically ill patients.
AI-estimated from published studies. Interpret as directional guidance.
Vitamin C has a higher evidence score (8/10 vs 6.5/10) and wins in 2 of 3 categories.
For support immune system, Vitamin C has a higher relevance score (85 vs 70).
No known interactions between Selenium and Vitamin C have been documented in our database. However, always consult a healthcare provider before combining supplements.