Most greens are superb sources of vitamin A, mostly in the form of beta carotene, which has been shown to help protect against cancer, heart disease, cataracts, and other diseases of aging through its antioxidant properties. Vitamin A also helps keep the immune system in tiptop shape. Othercarotenoids found in greens may be just as potent cancer conquerors as well, but research is continuing. The outer leaves of greens usually contain more beta carotene than do the inner leaves. Dandelion greens are bursting with twice the vitamin A of other greens.