Onions form the flavor base of so many cuisines that it's easy to include red onion in a wide range of meals. Because red onions are mild and sweet compared to other varieties of onion. Red onions supply a modest amount of vitamin C, an antioxidant that also strengthens your skin, bones, cartilage and hair. You'll also get a little bit of potassium, a mineral linked to cardiovascular health, as well as a small amount of iron, a mineral that promotes good oxygen circulation.