How We Grade Evidence
Understanding the A/B/C/D grading system that powers every supplement recommendation on SMILE.
Why Evidence Grading Matters
The supplement industry is flooded with marketing claims that often outpace the actual science. A product might claim to "boost immunity" or "enhance focus" based on a single, small study — or even no human studies at all. Evidence grading cuts through the noise by giving you an honest, standardized assessment of what the research actually shows.
Our grading system helps you distinguish between supplements with rock-solid evidence and those that are mostly hype. This way, you can prioritize what is most likely to work and avoid wasting money on unproven products.
The Four Grades Explained
Strong Evidence
Grade A is reserved for supplements backed by multiple high-quality human studies, including randomized controlled trials (RCTs) and systematic reviews or meta-analyses. The evidence is consistent across different populations and study designs.
Good Evidence
Grade B indicates promising evidence from well-conducted human studies, but with some limitations. There may be fewer studies available, smaller sample sizes, or some inconsistency in results. The overall direction of evidence is positive, but more research would strengthen the case.
Limited Evidence
Grade C means there is some scientific basis for the supplement's claimed benefits, but the evidence has significant limitations. Studies may be small, poorly designed, or primarily conducted in animals or cell cultures. Preliminary results are interesting but far from conclusive.
Insufficient Evidence
Grade D indicates that there is very little or no credible scientific evidence to support the supplement's claims. Evidence may be limited to anecdotal reports, theoretical mechanisms, or very early-stage research. We include these supplements for transparency, but they should be approached with caution.
Types of Studies We Consider
Not all studies are created equal. Here is the hierarchy of evidence we use, from strongest to weakest:
Systematic Reviews & Meta-Analyses
Pool data from multiple studies to draw stronger conclusions. The gold standard of evidence.
Randomized Controlled Trials (RCTs)
Participants are randomly assigned to treatment or placebo groups, minimizing bias.
Cohort Studies
Follow groups of people over time to observe outcomes. Good for long-term effects but cannot prove causation.
Case-Control Studies
Compare people with a condition to those without, looking for exposure differences.
Animal & In-Vitro Studies
Useful for understanding mechanisms but results don't always translate to humans.
Expert Opinion & Traditional Use
Considered as context but not as strong evidence on its own.
How We Evaluate Research
When assessing the evidence for a supplement, we consider multiple factors beyond just the number of studies:
- Study quality: Was it double-blinded? Was the sample size adequate? Was the study duration appropriate?
- Consistency: Do multiple studies reach the same conclusions? Are results reproducible across different research groups?
- Dosage relevance: Were the doses used in studies achievable through supplementation? Some studies use impractically high doses.
- Population relevance: Were participants healthy adults, or specific patient populations? Results in deficient populations may not apply to those with adequate levels.
- Conflict of interest: Was the study funded by a supplement manufacturer? We weigh industry-funded studies more carefully.
- Recency: More recent studies may use better methodologies or contradict earlier findings.
Real-World Examples
Vitamin D3 for bone health
Multiple meta-analyses and dozens of RCTs consistently show that Vitamin D3 supplementation (especially combined with calcium) significantly reduces fracture risk in deficient populations. The evidence is strong, consistent, and well-replicated.
View Vitamin D3 →Magnesium for sleep quality
Several RCTs suggest magnesium supplementation can improve sleep quality, particularly in older adults and those with low magnesium levels. While results are generally positive, some studies show modest effects and more large-scale trials would strengthen the case.
View Magnesium →Ashwagandha for stress reduction
A handful of small RCTs show ashwagandha may reduce cortisol levels and self-reported stress. However, studies are limited in size, some are industry-funded, and methodological quality varies. Promising but needs more rigorous research.
View Ashwagandha →Colloidal silver for immune support
Despite widespread marketing claims, there are no credible human studies supporting colloidal silver for immune health. The FDA has stated it is not generally recognized as safe or effective. Risk of side effects (argyria) further diminishes the risk-benefit profile.
Limitations & Transparency
No grading system is perfect. Here are important things to keep in mind:
- •Grades can change as new research is published. We regularly review and update our assessments.
- •A high grade for one benefit does not mean the supplement is effective for all claimed benefits.
- •Individual responses to supplements vary based on genetics, diet, health status, and other factors.
- •Our grades reflect the quality of evidence, not necessarily the magnitude of the effect.
- •Always consult a healthcare professional before starting any supplement regimen.