Micronutrients and oxidative stress in the aetiology of cancer

Innumerable epidemiological studies have revealed what are, on the whole, rather weak associations between types of food and the incidence of cancer (Table 1).In a comprehensive review of cancer epidemiology, Doll & Pet0 (1981) estimated the contribution of nutritional factors to cancer incidence at 35%, as significant as the contribution from smoking.However, the nature of the links between diet and this disease remains obscure.Only in a very few cases is it possible to identify the causative agent; for example, aflatoxin (a fungal toxin, known to be mutagenic, that occurs in foods such as nuts and grain stored in tropical conditions) is detected at high levels in populations in Africa at risk of liver cancer, apparently acting synergistically with hepatitis B infection (Wild & Montesano, 1991).On the other hand, a high intake of @-carotene is associated with low incidence of various cancers (Gerster, 1993).In general, though, there is little scientific substance in the provision of information to the public concerning foods that are 'good' or 'bad' in terms of cancer risk.The role of diet is complex.Food contains carcinogenic chemicals; Ames (1983) lists the natural components of food, mostly plant toxins, that have been shown to be mutagenic (i.e.positive in the Ames bacterial mutagenicity assay) or carcinogenic (i.e.cause cancer in laboratory animals).'Almost everything natural we eat contains