Vitamin E is an antioxidant. Antioxidants are substances that may protect your cells against the effects of free radicals. Free radicals are molecules produced when your body breaks down food, or by environmental exposures like tobacco smoke and radiation. Vitamin E also plays a role in your immune system and metabolic processes. Good sources of vitamin E are vegetable oils, margarine, nuts, seeds, and some leafy greens, but not all. Vitamin E is also added to foods like cereals. Most people get enough vitamin E from the foods they eat. People with certain disorders, such as liver diseases, cystic fibrosis, and Crohn’s disease may need extra vitamin E.