Although there is a substantial body of evidence that diets rich in plant foods (particularly fruit and vegetables) convey health benefits, as do high plasma levels of several antioxidant nutrients found in these foods, a causal link between lack of antioxi-dants and disease occurrence or between antioxidant administration and disease prevention remains to be established. There is a lack of understanding of the mechanisms underpinning the apparent protective effect of plant foods and, as yet, no clear picture of which components are effective and hence no way of predicting whether all or just some plant foods are important in this respect.

if future trials do demonstrate a reduction in chronic disease risk with antioxidant supplementation, this cannot be definitively attributed to the antioxidant effect of these nutrients because other biological functions may also play a role. For example, in addition to retarding LDL oxidation, vitamin E may help to protect against CVD via its action on platelet aggregation and adhesion or by inhibition of the proliferation of smooth muscle cells. Furthermore, although vitamin C, vitamin E, and selenium have been shown to decrease the concentration of some of the biomarkers associated with oxidative stress, the relationship between many of these biomarkers and chronic disease remains to be elucidated.

The intervention studies highlight the lack of information on the safety of sustained intakes of moderate to high doses of micronutrient supplements and long-term harm cannot be ruled out, particularly in smokers. Further evidence is required regarding the efficacy, safety, and appropriate dosage of antioxidants in relation to chronic disease.

Currently, the most prudent public health advice continues to be to consume a variety of plant foods.

See also: Antioxidants: Diet and Antioxidant Defense; Observational Studies. Ascorbic Acid: Physiology, Dietary Sources and Requirements; Deficiency States. Cancer: Epidemiology and Associations Between Diet and Cancer; Effects on Nutritional Status. Carotenoids: Chemistry, Sources and Physiology; Epidemiology of Health Effects. Coronary Heart Disease: Hemostatic Factors; Lipid Theory. Diabetes Mellitus: Etiology and Epidemiology; Classification and Chemical Pathology; Dietary Management. Lipoproteins. Lung Diseases. Selenium. Stroke, Nutritional Management. Vitamin E: Metabolism and Requirements; Physiology and Health Effects.

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