(This sheet is summary of links to the above website as of July 2004)
Dietary Antioxidants
There is much current interest in a possible role of dietary antioxidants in the prevention of CHD. As yet, there is no definitive answer, although there is mounting circumstantial evidence that foods rich in antioxidants probably do protect against CHD.
Antioxidants in foods are derived from two broad categories: (i) nutrients which play other essential roles (vitamins C, E and b-carotene, selenium etc) and (ii) a multitude of other so called non-nutrients, such as other carotenoids, polyphenols and flavonoids.
Potential mechanisms by which antioxidants protect against CHD include:
(i) prevention of the lipoprotein oxidation which may predispose to atherosclerosis;
(ii) possible restoration of normal endothelial function in people with early atherosclerosis;
(iii) possible protection of the myocardium from ischaemic damage.
Very large population studies have shown lower rates of CHD among people eating higher amounts of fruits and vegetables which are rich sources of antioxidants (1). While such studies are encouraging, it is difficult to exclude some degree of confounding (i.e. people who eat more fruit and vegetable may also have healthier lifestyles in other ways). The rate of CHD death has been observed to be considerably lower in people who eat the most vitamin E in foods such as vegetable oil products (including polyunsaturated margarines) and nuts (2). Other large studies have suggested that vitamin E supplementation (3) rather than vitamin E-containing foods protect against CHD.
Flavonoids are a class of polyphenolic antioxidants present in apples, onions and tea (green and black). A large study from Finland has recently reported less than half the rate of CHD death among people who ate the most flavonoids as components of their diets (4). This confirmed an earlier, smaller study from Holland.
The status of b-carotene is uncertain. Although randomised controlled trials of supplemental synthetic b-carotene have not supported a benefit of this vitamin, two large observational studies have indicated that the consumption of carotenoids in food is associated with a lower incidence of CHD, especially among smokers (5,6).
The isoflavones are another class of polyphenols which are present in soybean. These have been postulated but not proven to be a protective factor in Asian diets (7). Other polyphenols e.g. those in olive oil, tea and red wine have also been proposed as protecting against CHD because of their proven antioxidant potential (8) but proof through either prospective clinical trials or clear-cut observational studies is still lacking.
Other antioxidant vitamins such as vitamin C have not yet been implicated in the protection against CHD.
- There is circumstantial evidence that dietary antioxidants, especially vitamin E and flavonoids protect against CHD mortality.
- Plausible mechanisms for a protective role of antioxidants have been demonstrated.
- Foods rich in vitamin E and flavonoids are recommended components of a healthy diet. These foods include vegetables, fruits, vegetable seed oils, nuts and probably soybeans, tea and grape products.
- Possible benefits of supplemental antioxidants are limited to vitamin E on current evidence, although even in this case there are still no intervention trials showing unequivocal benefit.
- Rimm, E.B. et al. JAMA 1996;275:447-451.
- Kushi, L.H. et al. NEJM 1996;334:1156-1162.
- Stampfer, M.J. et al. NEJM 1993;328:1444-49.
- Knekt, P. et al. BMJ 1996;312:478-481.
- Street, D.A. et al. Circulation 1994;90:1154-61.
- Kardinaal, A.F.M. et al. Lancet 1993;342:1379-84.
- Adlercreutz,H. et al. Lancet 1993;342:1209-1210.
- Renaud, S. et al. Lancet 1992;339:1523-26.
May 1997
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