How to Read Supplement Research

Reading supplement research can feel overwhelming. But you don’t need a PhD to spot good studies from bad ones. A few basic concepts will take you most of the way.

RCTs vs. observational studies. Randomized controlled trials (RCTs) are the gold standard. Participants are randomly assigned to take the supplement or a placebo. This controls for other factors that might affect the results. Observational studies just watch what people do naturally. They can show correlations, but they can’t prove a supplement caused anything. When someone says “studies show this supplement works,” ask if those were RCTs or observational. It matters.

Sample size matters. A study with 15 people can’t tell you much. Results from small trials bounce around a lot due to random chance. Look for studies with at least 50 to 100 participants per group. Bigger is almost always better. When we pool multiple small studies in a meta-analysis, we get more reliable estimates, but we’d still prefer large trials.

Effect sizes matter more than p-values. A study might say a result is “statistically significant” (p < 0.05). That sounds impressive, but it doesn’t tell you if the effect is actually meaningful. A blood pressure drop of 0.5 mmHg could be statistically significant with enough participants, but it won’t change your health. Effect sizes tell you how big the difference really is. We report Hedges’ g on this site. A g of 0.2 is small, 0.5 is medium, and 0.8 is large. Always ask: “How big is the effect?” not just “Is it significant?”

Watch out for industry-funded studies. Research funded by supplement companies isn’t automatically wrong. But studies funded by the companies that sell the product tend to find more positive results than independent research. It’s a well-documented pattern. Check the funding disclosure at the bottom of any study. If a brand paid for it, don’t dismiss it, but weigh it accordingly.

Want to see how we apply these principles? Check out How We Rate Supplements for a full breakdown of our process.