Onions and relatives (shallots, garlic, leeks, chives and spring onions) are known for their healing properties. They are a very good source of vitamin C, B6, biotin, chromium, calcium and dietary fibre. Onions are a rich source of quercetin, a potent antioxidant known for inhibiting stomach cancer.
Onions also contain good amounts of folic acid and vitamin B1 and K.
Onions also have the enzyme alliinase, which is released when an onion is cut or crushed and it causes your eyes to water. They also contain flavonoids, which are pigments that give vegetables their colour. These compounds act as antioxidants, have a direct anti-inflammatory effect and boost the immune system.
A 4 minute video explaining more about onions: