Do antioxidants prevent disease?
Summary of a HEN network member’s report
The issue
While oxygen is necessary for human life, it can also damage cells when certain chemical processes create oxygen free radicals. These radicals contribute to aging and are involved in the onset of many diseases, including arteriosclerosis and cancer. Numerous substances called antioxidants, found in nature and in the body, function as protective agents against oxygen free radicals. Among the best known antioxidants are vitamins C and E, beta-carotene, selenium, ubiquinone (Q10) and the flavonoids found in wine, apples, onions and tea.
There is a common belief that the extra intake of antioxidants is beneficial, which has led to the widespread use of antioxidant products.
Findings
The scientific literature on antioxidants is extensive and difficult to review and interpret. In 1997, SBU, an independent health technology assessment agency, reviewed 1300 studies in the field. It found no evidence that manufactured antioxidants have any positive effect in preventing disease, except in the case of Vitamin C, where weak evidence showed that large daily doses can relieve, but not prevent, the common cold. The literature had little evidence to indicate that supplementing the diet with antioxidants can prevent cardiovascular diseases, diabetes, neurological disorders, rheumatoid arthritis or cancer. In fact, some dietary supplements have negative effects, particularly at high doses. However, there is some evidence that natural antioxidants (from fruits, vegetables, wine etc.) may prevent several diseases.
Policy considerations
- Studies have shown that a diet rich in antioxidants, which are primarily provided by fruits and vegetables, may help prevent a variety of serious diseases.
- However, there is no scientific evidence to show that supplemental antioxidants, beyond those found in a balanced diet that includes fruits and vegetables, will prevent disease. As of 1997, hypotheses presented in this field had yet to be scientifically verified.
- Controlled scientific studies have shown that high doses of beta-carotene and vitamin E supplements can create serious negative effects in smokers.
The views expressed in this summary are based on a publication of a HEN Network member agency and do not necessarily represent the decisions or stated policy of WHO/Europe.
