An Overview of the epidemiological evidence linking diet and cancer

Abstract

There is now uniform agreement among oncologists that the incidence of cancer is determined, in large part, by factors in the environment and aspects of behaviour that are capable of modification or avoidance. It is agreed, too, that by such means the age-specific incidence of the disease in middle and old age could be reduced by some 8 0 4 %. That the percentage should be so high should not be surprising, when it is borne in mind that we now know about fifty causes of human cancer that are responsible, between them, for about 40% of all the cancers that occur annually throughout the world, while in this country tobacco alone is responsible for about one-third of all cancer deaths. It may be surprising, however, that diet is also commonly suggested to be responsible for about 30-70% of the total, when so few aspects of diet have been established as causes of the disease. This value of 30-70% is, in fact, a guess based partly on the knowledge that the diet of experimental animals has a major influence on the incidence of cancer produced by treatment with a variety of laboratory carcinogens, and partly on the simplistic belief that what you put into your mouth and pass into or through the digestive tract is likely to play a large part in the production of cancers of the corresponding organs which, in Britain, are responsible for 30% of all cancers. That up to 70% has been thought to be possibly attributable to diet should not, however, be surprising when it is borne in mind that the production of cancer is a process, the progress of which may be influenced by many factors, and that the avoidance of each factor individually can have the same final effect. We can, therefore, properly say that two factors may each be separately responsible for (say) 80-90%0 of the risk of developing a particular type of the disease, while the avoidance of both will have little more effect than the avoidance of one. Examples include smoking and exposure to asbestos in the production of cancer of the lung, smoking and the consumption of alcohol in the production of cancers of the mouth, pharynx, and oesophagus, and infection with hepatitis B virus and the consumption of aflatoxin in the production of cancer of the liver. It is quite possible, therefore, that dietary modification could help to reduce the incidence of cancers that are now known to be due to tobacco, occupational hazards, viral infection, ultraviolet light, and ionizing radiation, even if these hazards continued