This has become an important subject and an enormous amount of research is going on to investigate it. In 1997 the World Cancer Research Fund, in association with the America Institute for Cancer Research, published a 670-page book called Food, Nutrition and the Prevention of Cancer. As may be expected, a book as recent as this contains a great deal of information about antioxidant vitamins. It also contains an enormous amount of detail about the effects on the incidence of various kinds of cancers of diets that are low in vegetables and fruit.
So far as vitamin C is concerned, there is now clear evidence that people with low dietary vitamin C intake – that is, people who do not eat much in the way of vegetables and fruit – are more likely to get most forms of cancer than people who eat normal amounts of C-containing food. Here is a brief summary of the diet and cancer findings derived from numerous research projects.
- The risk of cancers of the mouth and throat is decreased by diets high in fruit and vegetables.
- The risk of cancers of the larynx is lower in those with diets high in fruit and vegetables.
- The risk of cancer of the oesophagus is reduced in people whose diets are high in fruit and vegetables.
- There is convincing evidence that diets high in fruit and vegetables are protective against cancer of the lung
- Five trails of vitamin C found a significant or strongly protective effect against lung cancer.
- Diets high in fruit and vegetables appear to protect against pancreatic cancer.
- Diets high in vegetables decrease the risk of colon and rectal cancer.
- Diets high in vegetables and fruit probably decrease the risk of breast cancer.
- The most effective dietary way of avoiding cancers of the ovary and the lining of the womb is to ensure a high intake of fruit and vegetables.
- Diets high in vegetables and low in animal fats offer some protection against prostate cancer.
- Diets high in vegetables and fruit probably protect against bladder cancer.
- There is, as yet, no convincing evidence that dietary factors can affect cervical cancer.
So far as trials of antioxidant vitamin supplements are concerned, the evidence is, until now, scanty. Unfortunately, most of the trails of supplements have used combinations, many including beta-carotene, and we now know that beta-carotene supplements cause more harm than good. Some research, however, came up with encouraging results. In one trial, daily supplements of 50 mg of vitamin E was associated with a 34% reduction in the incidence of prostate cancer, but had no effect on lung cancer. An Italian trial of supplementary vitamins C and E showed a significant reduction n precancerous polyps of the colon in predisposed people. Other trials showed no protective effect in this condition ( familial polyposis). The precancerous mouth condition of leukoplakia was caused wholly or partially to disappear in 65% of people who were given vitamin E supplements of 400 mg twice a day for 24 weeks. A large study of women’s health involving 40,000 American women includes vitamin E supplements, but this has not yet been completed.