'If you’ve been eating an apple a day to keep the doctor away, you would be wise to add an onion a day to that regimen. This humble vegetable is a member of the Allium genus, making it closely related to other superfoods like garlic, leeks, scallions, and chives.
This means onions are rich in sulfur-containing compounds that give them both their characteristic odor and much of their health-boosting potential.
As one of the oldest cultivated plants, onions do not disappoint in terms of nutrition. They’re a very good source of vitamins C and B6, iron, folate, and potassium. But it’s their phytochemicals – including the flavonoid quercetin and allyl disulphide – that are most exciting to researchers.'