Garlic

Garlic is a perennial herb 0.3–1 m tall that forms clumps of bulbs below ground, with 4–12 flat, strap-shaped leaves 6–12 mm wide and sheathing bases. The rounded bulb divides into 4–15 cloves wrapped in white or pale-purple papery skins, each clove being in fact an accessory bud. The flower scape, about 25 cm tall, bears a spherical umbel of greenish-white to pinkish flowers with six perianth segments roughly 3 mm long; bulbils are usually mixed in among the flowers and viable seed is hardly ever produced outside the laboratory. The chromosome number is 2n = 16.

According to Kew's Plants of the World Online, the native range of Allium sativum is restricted to Central Asia and north-eastern Iran — Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, Uzbekistan and Iran — where it grows in rocky valleys, riverbeds and stream sides of the temperate biome. Yet garlic is today known only as a crop: it was domesticated thousands of years ago (its nearest wild relative is A. longicuspis of the Tien Shan), is recorded in Egypt around 3000 BC and reached India, China and the Mediterranean in antiquity. It is now cultivated on every continent between 5° and 50° latitude, world production amounting to some 10 million tonnes a year, dominated by China. In Vietnam it is grown in the winter–spring season in the north (Hai Duong) and on Ly Son island.

Garlic's activity comes overwhelmingly from its sulphur chemistry. Intact cells store odourless alliin (S-allyl cysteine sulfoxide); when a clove is crushed or damaged the released enzyme alliinase converts alliin into allicin (diallyl thiosulfinate), the most abundant thiosulfinate — about 70% of the total thiosulfinates of fresh garlic, roughly 0.4% of fresh weight, or 4–5 mg per clove. Allicin is highly unstable and breaks down into diallyl sulphide (DAS), diallyl disulfide (DADS), diallyl trisulfide (DATS), ajoene, 2-vinyl-4H-1,3-dithiin and S-allyl cysteine (SAC) during heating or storage. Fresh garlic also contains more than 20 phenolics (chiefly β-resorcylic acid, quercetin, rutin, gallic acid and pyrogallol), saponins (purple clones hold about 40 times more than white ones), fructan polysaccharides (around 85% fructose) and micronutrients such as selenium, manganese and vitamins C and B6.

Garlic has been both food and medicine for millennia; in 1944 Cavallito and Bailey isolated allicin, the so-called 'heart of garlic'. A systematic review and meta-analysis in Nutrition Reviews (2025), pooling 108 RCTs with 7,137 participants, found that garlic supplementation lowered triglycerides (WMD −5.82 mg/dL), total cholesterol (−10.21 mg/dL), LDL-cholesterol (−5.90 mg/dL), systolic (−3.71 mmHg) and diastolic blood pressure (−1.97 mmHg), while raising HDL (+2.18 mg/dL) and improving C-reactive protein and total antioxidant capacity. An umbrella review of 16 meta-analyses (2019) reported a reduced risk of gastric cancer (RR 0.78; 95% CI 0.67–0.91) and clearer benefits in people with dyslipidaemia, hypertension and diabetes. Allicin has antibacterial and antifungal activity through oxidation of pathogen thiol groups (Trends in Food Science & Technology, 2019), while SAC and garlic polysaccharides act as immunomodulators. In practice, garlic is used for colds and indigestion in traditional medicine, processed into tablets, extracts and black garlic, and applied in organic farming to repel fungal diseases and insects.

Garlic is generally safe as a food; high doses may cause heartburn, bloating, body odour and (rarely) allergy, while the 2019 umbrella review found only limited side effects, namely garlic breath and gastrointestinal discomfort. Because it has antiplatelet activity, caution is advised alongside anticoagulants (warfarin, aspirin) or before surgery; pregnant women and anyone on prolonged high doses should consult a health professional. The species is not globally threatened because all production is farmed, yet millennia of vegetative propagation have left it with low genetic diversity and many local landraces at risk of being lost. Conservation rests on gene banks in the Czech Republic, Israel, Spain, Taiwan, India and Japan plus the maintenance of local cultivars such as Ly Son and Hai Duong garlic; POWO confirms the narrow native range in Central Asia to north-eastern Iran, where natural habitats of the species and its wild Allium relatives need protection.