Reading the Evidence: Why Study Type Matters More Than Headlines

Most confusion in longevity conversation comes from one place: treating every study as equivalent. **Human clinical evidence.** Controlled human trials are the strongest category available. Randomisation and blinding reduce the influence of expectation and selection, which is why regulators rely on them. **Human observational evidence.** Useful for generating hypotheses and describing populations, but it cannot establish causality with the same confidence as a controlled trial. **Animal and preclinical research.** Essential for understanding mechanism. It cannot be translated automatically into human outcomes — physiology, dosing and lifespan all differ. **In-vitro research.** Valuable for mechanistic detail. A pathway demonstrated in a dish is not proof of an effect in a person. **Theoretical and emerging research.** Plausible reasoning that has not yet been tested adequately. It should always be labelled as such. When we describe a compound, we state which of these categories the evidence belongs to. That is the entire difference between education and marketing.