Onion has been cultivated for over five thousand years, among the oldest continuously cultivated vegetables in human history, with documented medicinal and dietary use across ancient Egyptian, Indian, Chinese, and Mesopotamian civilizations independently. Ancient Egyptians reportedly used onions in burial and religious practices, believing the bulb's concentric-ring structure symbolized eternal life.
Onion's close botanical relationship to garlic, another prominently featured remedy in this Atlas, means the two share overlapping traditional uses and some similar active compounds, though onion's own modern clinical evidence base has developed somewhat independently.
Onion has real, dedicated meta-analysis evidence for cholesterol specifically. A meta-analysis of 10 randomized controlled trials (446 participants) found onion supplementation significantly improved HDL cholesterol, reduced LDL cholesterol, and reduced total cholesterol, though found no significant effect on triglycerides.
Where the evidence is weaker: a direct, well-designed randomized trial specifically testing quercetin-rich onion skin extract on blood pressure found no significant effect in overweight patients with elevated blood pressure. This is notable, since quercetin itself (as an isolated supplement, from any dietary source) does show a positive blood pressure effect in separate meta-analyses — meaning onion's specific quercetin content and preparation may not translate the same way as concentrated quercetin supplements do. Given a genuine positive cholesterol evidence base but a directly negative trial for the blood-pressure claim often attached to onion, "Limited-Moderate" is the accurate, nuanced rating.
Eaten raw, cooked, or roasted; juiced; used in an enormous range of traditional cuisines worldwide as both a food staple and folk remedy.