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Head-to-head evidence comparison — which supplement is right for you?
Spirulina wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Likely helps
18 of 23 studies with measurable effects showed benefit.
Top outcomes
Verdict
Likely helps
11 of 12 studies with measurable effects showed benefit.
Top outcomes
100-200mcg
With food
Selenomethionine (best absorbed)
3-10g daily
With food to mask taste, Morning for energy, Before meals for appetite effects
Powder or tablets
4-8 weeks
4-8 weeks
8-12 weeks
4-8 weeks
2-4 weeks
Immediate
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.
Systematic Review of the Effects of Plant-Based Foods on Metabolic Outcomes in Adults with MASLD and Comorbidities Such as Obesity, Metabolic Syndrome, and Type 2 Diabetes
Nutrients (2025) · Systematic review
Background: Metabolic dysfunction-associated steatotic liver disease (MASLD) has become one of the most prevalent liver diseases, affecting up to 40% of adults and strongly associated with obesity and metabolic dysfunction.
The Role of Chlorella and Spirulina as Adjuvants of Cardiovascular Risk Factor Control: A Systematic Review and Meta-Analysis of Randomised Controlled Trials
Nutrients (2025) · Meta analysis · n=12
On the other hand, Spirulina intake led to a significant reduction in diastolic BP (-0.42, 95% CI: -0.81 to -0.02, p = 0.04) but did not significantly affect lipemia indexes, despite a trend toward a reduction in total cholesterol (-0.17, 95% CI: -0.39 to 0.06, p = 0.15).
Edible Algae Reduce Blood Pressure in Humans: A Systematic Review and Meta-Analysis of Randomised Controlled Trials
Journal of human nutrition and dietetics : the official journal of the British Dietetic Association (2025) · Meta analysis · n=1583
Edible algae intake significantly reduced systolic BP (SBP: -2.05 mmHg; 95% CI: -3.80, -0.31; p = 0.022) and diastolic BP (DBP: -1.87 mmHg; 95% CI: -3.10, -0.64; p = 0.001).
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 multiple meta-analyses showing dose-dependent effects. LDL reduction of ~33mg/dL and triglycerides ~39mg/dL reported. Effects appear to plateau above 8-10g daily.
AI-estimated from published studies. Interpret as directional guidance.
Spirulina has a higher evidence score (9/10 vs 9/10) and wins in 2 of 3 categories.
Both Selenium and Spirulina score equally (70) for support immune system.
No known interactions between Selenium and Spirulina have been documented in our database. However, always consult a healthcare provider before combining supplements.