Of all the chronic diseases in which excess oxidative stress has been implicated, cardiovascular disease has the strongest supporting evidence. Oxidation of low-density lipoproteins may be a key step in the development of coronary atherosclerosis. Epidemiological studies indicate that diets rich in fruits and vegetables, vitamin C, vitamin E, and carotenoids are associated with a decreased risk of coronary heart disease. However, no randomized prospective studies have documented a favorable effect of vitamin C or carotenoids on cardiovascular morbidity and mortality. Four studies have examined the effects of vitamin E; only one reported a positive benefit while the other three were neutral. Thus available data do not adequately substantiate the premise that increasing the intake of vitamin C, vitamin E, or β-carotene and other carotenoids will reduce the risk of coronary heart disease. Ongoing randomized trials among high-risk, apparently healthy individuals and among patients with cardiovascular disease are expected to provide evidence useful in resolving this issue.
A number of observational epidemiological studies have examined the relationship between intakes of vitamin C, vitamin E, and carotenoids and the presence of cataracts in humans. Several studies indicate a lowered risk of cataracts associated with either an increased serum level of these dietary components or supplement use. These studies, since observational in nature, do not constitute at this time a sufficient basis for a conclusion that these dietary components can prevent cataracts in humans.
Epidemiological studies find a decreased likelihood of age-related macular degeneration (AMD) associated with higher intakes of fruits and vegetables, especially those that are rich in the carotenoids lutein and zeaxanthin. Protective effects of lutein and zeaxanthin are biologically plausible because these carotenoids selectively accumulate as the pigment of the macular region of the retina and account for the yellow color observed in this region. The association has also been observed in smokers, who have lower plasma levels of carotenoids and are also at an increased risk of developing AMD. However, all reports are associative in nature and have not