How to Read Our Evidence
What does "15 studies" actually mean? Here's how to interpret what you see on NutriVouch.
Is more studies always better?
Not really. In evidence-based medicine, the type and quality of studies matter much more than the count. One well-designed meta-analysis with thousands of participants is more valuable than 50 small studies with conflicting results. Cochrane Reviews — the gold standard of medical evidence — typically include just 5–15 studies per question.
Why do study counts vary so much?
Some substances like Vitamin D have been studied for decades — over 600 trials across many health goals. Newer compounds like NMN or Spermidine only have a handful of human RCTs because clinical research takes years and funding. A low study count doesn't mean a substance doesn't work — it means we simply don't know enough yet.
What are the confidence tiers?
Confidence Tiers
with at least 1 meta-analysis
Extensively studied with consistent results. Conclusions are reliable and unlikely to change with new research.
Examples: Vitamin D, Omega-3, Probiotics, Magnesium
majority showing positive results
Well-researched with mostly consistent findings. Effects are generally established but more research could refine them.
Examples: Saffron, Ashwagandha, Apigenin
early but promising
Preliminary research suggests potential effects, but findings need replication in larger trials.
Examples: Spermidine, Apple Cider Vinegar, Tongkat Ali
more research needed
Not enough quality human research yet to draw conclusions. Substance may still work, but we can't tell from current data.
Examples: Shilajit, Fisetin (for some goals)
What counts as a 'study' here?
We only include human clinical research from PubMed — the world's largest biomedical database. Animal studies, test-tube experiments, and case reports are excluded from our scoring. Each study must pass quality checks: clear methodology, reasonable sample size, and reported results.
Why do study types have different weights?
Not all studies are equal. The scientific community recognizes a hierarchy:
Study Hierarchy
Meta-Analysis
Combines results from many studies — strongest evidence
Systematic Review
Comprehensive analysis of all available research
Randomized Controlled Trial
Participants randomly assigned, reduces bias
Cohort Study
Observes groups over time — useful but observational
Case-Control Study
Compares groups retrospectively
What if studies show conflicting results?
We track this. When most studies show positive effects, confidence increases. When findings are mixed or mostly null, scores reflect that uncertainty. A substance with 20 studies but conflicting results gets a more cautious score than 20 studies showing consistent benefit.
Why isn't [my favorite supplement] rated higher?
Popular doesn't mean proven. Many widely-marketed supplements have weaker evidence than less famous ones. We base scores strictly on published clinical research, not marketing claims, social media trends, or testimonials. Our goal is honesty, not popularity.
The bottom line
When you see a substance with 15 well-designed human studies and a positive meta-analysis, that's strong scientific support. When you see 2 small RCTs from one lab, treat the findings as preliminary. We're here to give you the data — interpret it with appropriate caution.