Instead of taking antioxidants, researchers now think you should aim to prevent your mitochondria from making excessive amounts of oxidants. The cells of your body have tiny chambers in them called mitochondria that help convert food to energy. When they do this, they knock of electrons from nutrients, and these extra electrons eventually end up attached to oxygen. Electron-charged oxygen, called reactive oxygen species or free radicals, then attach to the DNA cells to damage them and shorten your life.
At this time, scientists have found only one practical way to reduce the amount of oxidants produced by mitochondria: exercise. Vigorous exercise helps the mitochondria burn food more cleanly with the production of fewer oxidants. The same effect can be accomplished with severe calorie restriction, or with chemicals such as resveratrol or dichloroacetate, but the results of these studies in animals have not yet been successfully applied to humans.
Here's another study showing that taking antioxidant vitamins does not prevent heart attacks ( Archives of Internal Medicine, August 2007). 8,171 women over the age of 40, all with a history of heart disease or with three or more risk factors for that disease (high blood pressure, diabetes or high cholesterol) were randomly assigned into groups and given either 500 milligrams of ascorbic acid (vitamin C) every day, 600 units of vitamin E every other day or 50 milligrams of beta carotene every other day. None of the antioxidant vitamins, either alone or in combination, helped reduce the risk of a heart attack. As of today, there is no evidence that taking antioxidants vitamin pills helps prevent heart attacks. More on cell mitochondria