Antioxidants are produced by your body and also found in food; plant-based sources such as fruits and vegetables are particularly rich in them. They help defend your cells from damage caused by potentially harmful molecules known as free radicals. Your body naturally produces free radicals when you exercise and digest food. However the environment, in terms of UV exposure, air pollutants, tobacco smoke and industrial chemicals like pesticides, is also sources of free radicals. Your body uses antioxidants, such as vitamins A, C, and E and the mineral selenium, to balance free radicals.  

When free radicals accumulate, they may cause a state known as oxidative stress. Scientists believe free radicals can contribute to the aging process and may play a part in diseases such as diabetes and heart disease. Antioxidant supplements are commonly considered healthy but can be problematic when taken in excess.