Evidence that fruit and vegetables may protect against
coronary heart disease is accumulating. It is unclear which constituents of fruit and vegetables are responsible for this protective effect.
Folate as a co-substrate in
homocysteine metabolism may be important. An intake of about 400 micrograms
folate equivalents/day seems to be required to achieve stable low
homocysteine blood levels. Five of eight epidemiologic studies show significant inverse associations between
folate and
cardiovascular disease. These associations could be confounded by
antioxidant vitamins and/or other substances. In trials examining an association between
folate and
cardiovascular disease such confounding must be excluded, before specific recommendations can be given. Observational studies suggest that
vitamin C plays a role in the aetiology of
cardiovascular disease, but there are no completed intervention trials of this
vitamin alone. With regard to
vitamin E two cohort studies point to cardiovascular benefits with the long-term use of supplements of at least 100 IU/day, but the results of controlled trials are inconclusive. There is some evidence from observational studies of an inverse association between
beta-carotene and
cardiovascular disease, particularly in smokers. Intervention trials do not support this hypothesis, rather, they suggest a possible harmful effect of
beta-carotene supplements in smokers. Nevertheless, protective effects of
beta-carotene and
vitamin E in different dosages, durations of administration, or different combinations are still possible. The last paragraph of this review discusses limitations of the present and priorities of future research.