Red onions are absolutely jammed packed with vitamins and minerals including vitamin C, K, B6, calcium, magnesium, potassium, manganese and folate. Not only are they the most vibrant of the onion family, but they're one of the healthiest too. Red onion also contains a higher amount of antioxidant compounds than the white onion and contains at least 25 different anthocyanin too. Among other health benefits, red onions contain antioxidants, flavonoids. Antioxidants are important because they are fighting the free radicals.