This study attempts a systematic evaluation of the clinical evidence for the use of odourless garlic prepared by ageing or fermentation. By PubMed, CENTRAL, and handsearching, 59 clinical studies were identified for potential extraction, of which 24 fulfilled the inclusion criteria. The quality of the studies and evidence of effectiveness were assessed by an established set of conventional criteria. Even the 12 best clinical trials (50%) had fundamental flaws that prevented to grade them as confirmatory. On the basis of a subsample of 19 exploratory studies (79%), an impressive reduction of cardiovascular risk was found for odourless garlic (evidence of effectiveness, “moderate” and for other indications, “poor”). Evidence of effectiveness is further limited by the fact that most studies used aged garlic produced by one pharmaceutical company and that products differed in composition and dose of the marker substance S-allyl-cysteine. In case odourless garlic is potentially an effective remedy in particular for cardiovascular diseases, we discern an urgent need for long-term confirmatory studies. The ultimate cardiovascular endpoint for definitive studies would be mortality, but reductions in blood pressure or demonstrable decreases in atherosclerotic plaques or blood markers of cardiovascular risk would be useful surrogates. Sample sizes for various assumptions are provided.
Keywords: aged garlic; black garlic; clinical effectiveness; fermented garlic; odourless garlic.