Free radicals, such as superoxide, hydroxyl ions and nitric oxide all contain an unpaired electron. These radicals can have a negative effect on cells causing oxidative damage that leads to cell death. Antioxidants, such as vitamin E, prevent cell damage by binding to the free radical and neutralising its unpaired electron. For example, when vitamin E binds to OO· or O2· they form an intermediate structure that is converted to a-tocopherylquinone. A recent population based study of antioxidants concluded that a diet rich in foods containing vitamin E might help protect some people against Alzheimer’s disease (AD). Vitamin E in the form of supplements was not associated with a reduction in the risk of AD.