Research in the area of antioxidant supplementation has produced conflicting data. Discuss the ...

Antioxidant supplements appear to work in some studies of cancer prevention and the prevention of cardiovascular disease, but not in others. The human body is very complex, as is the development and progression of the numerous forms of cancer. Some limitations of these types of studies are:

1.    It is impossible to control for all the possible factors involved in cancer and cardiovascular disease, and this clouds the relationship between the supplements and the diseases. There are many unknown factors as well, which may also affect study outcomes. For example, beta-carotene and some other carotenoids are known to have antioxidant properties in vitro, but it is not clear whether the antioxidant activity actually occurs in humans. Also, supplementation studies conducted in laboratory animals and test tubes show that individual nutrients act as antioxidants, however when conducted in humans, the benefits are not consistent.

2.    It has been suggested that taking antioxidants in supplement form may cause them to act as pro-oxidants in some situations, but consuming antioxidants in the form of food may provide these nutrients in a more balanced state. Thus, there may be differences across studies using whole foods versus supplements.

3.    There are interactions between antioxidant supplements and components of whole foods, such phytochemicals, which work together to reduce the risk for may types of cancer. Soluble fibre, folate, and a variety of phytochemicals found in fruits, vegetables, whole grains and tea are believed to be protective against heart disease. It is difficult to separate out these various factors that can affect study outcomes.

4.    Cancer and cardiovascular disease can take years to develop, and trials of supplements may be too short in duration. Individuals vary widely in their susceptibility to these diseases and their responses to protective factors and to factors that promote disease, and this means that they may need to be followed for many years in order to determine whether supplements have been protective or not.