As your brain burns fuel, such as sugar and oxygen, some by-products accumulate, just as soot gradually accumulates in a furnace. The burning is called oxidation; the by-products are particles called free radicals, a form of oxygen altered so that it always wants to combine with substances in the membranes of nerve cells.
This ‘sticking’ to nerve cells not only damages how they function, but eventually kills them. Some substances, particularly vitamin C and vitamin E, can mop up free radicals caused by oxidation. Thus, they are called “antioxidants.”