Approximately 200 studies that examined the relationship between fruit and vegetable intake and cancers of the lung, colon, breast, cervix, esophagus, oral cavity, stomach, bladder, pancreas, and ovary are reviewed. A statistically significant protective effect of fruit and vegetable consumption was found in 128 of 156 dietary studies in which results were expressed in terms of relative risk. For most cancer sites, persons with low fruit and vegetable intake (at least the lower one-fourth of the population) experience about twice the risk of cancer compared with those with high intake, even after control for potentially confounding factors. For lung cancer, significant protection was found in 24 of 25 studies after control for smoking in most instances. Fruits, in particular, were significantly protective in cancers of the esophagus, oral cavity, and larynx, for which 28 of 29 studies were significant. Strong evidence of a protective effect of fruit and vegetable consumption was seen in cancers of the pancreas and stomach (26 of 30 studies), as well as in colorectal and bladder cancers (23 of 38 studies). For cancers of the cervix, ovary, and endometrium, a significant protective effect was shown in 11 of 13 studies, and for breast cancer a protective effect was found to be strong and consistent in a meta analysis. It would appear that major public health benefits could be achieved by substantially increasing consumption of these foods.

Fruit, vegetables, and cancer prevention: A review of the epidemiological evidence

Epidemiologic evidence of the protective effect of fruit and vegetables on cancer risk

It has been estimated by various authorities that about one-third of cancers in Western high-income societies are attributable to factors relating to food, nutrition and physical activity. Identifying with confidence specific associations between dietary patterns, foods, body composition or individual nutrients is not simple because of the long latent period for cancer development, its complex pathogenesis and the challenge of characterising the multidimensional aspects of diet and activity over a lifetime. Reliable conclusions must therefore be drawn not only from randomised controlled trials but from a variety of methodological approaches, judged within a classic framework for inferring causality. Using a newly-developed method with a protocol for standardising the literature search and for analysis and display of the evidence, nine independent academic centres have conducted systematic reviews addressing the causal associations between food, nutrition and physical activity and risk of development of seventeen cancers, as well as of weight gain and obesity. A review has also examined the efficacy of such interventions in subjects with cancer. The reviews have been assessed by an independent Panel of twenty-one international experts who drew conclusions with grades of confidence in the causality of associations and made recommendations. Recommendations are given as public health goals as well as for individuals.

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The second World Cancer Research Fund/American Institute for Cancer Research expert report. Food, nutrition, physical activity, and the prevention of cancer: a global perspective.

The epidemiologic literature on the relationship between vegetable and fruit consumption and human cancer at a variety of sites was reviewed systematically in Part I.1 It was concluded that consumption of higher levels of vegetables and fruit is associated consistently, although not universally, with a reduced risk of cancer at most sites, and particularly with epithelial cancers of the alimentary and respiratory tracts. Possible mechanisms by which vegetable and fruit intake might alter risk of cancer are addressed here. A large number of potentially anticarcinogenic agents are found in these food sources, including carotenoids, vitamins C and E, selenium, dietary fiber, dithiolthiones, glucosinolates and indoles, isothiocyanates, flavonoids, phenols, protease inhibitors, plant sterols, allium compounds, and limonene. These agents have both complementary and overlapping mechanisms of action, including the induction of detoxification enzymes, inhibition of nitrosamine formation, provision of substrate for formation of antineoplastic agents, dilution and binding of carcinogens in the digestive tract, alteration of hormone metabolism, antioxidant effects, and others. It appears extremely unlikely that any one substance is responsible for all the associations seen. Possible adverse effects of vegetable and fruit consumption are also examined. One way to consider the relationships reviewed here is to hypothesize that humans are adapted to a high intake of plant foods that supply substances crucial to the maintenance of the organism, but only some of which are currently called ‘essential nutrients.’ Cancer may be the result of reducing the level of intake of foods that are metabolically necessary—it may be a disease of maladaptation.

Vegetables, fruit, and cancer. II. Mechanisms.

Botanicals have been used for the treatment of various human diseases throughout history. In addition, botanicals play a role in disease prevention. For example, epidemiologic studies have suggested that a reduced risk of cancer is associated with high consumption of vegetables and fruits. Thus, the cancer chemopreventive potential of naturally occurring phytochemicals is of great interest. In this review, we discuss the cancer chemopreventive activity of cruciferous vegetables such as cabbage and broccoli, Allium vegetables such as garlic and onion, green tea, Citrus fruits, tomatoes, berries, ginger and ginseng, as well as some medicinal plants. In addition, methods for the discovery of active compounds from plant sources are described. Several lead compounds, such as brassinin (from cruciferous vegetables like Chinese cabbage), sulforaphane (from broccoli) and its analog sulforamate, withanolides (from tomatillos), and resveratrol (from grapes and peanuts among other foods), are in preclinical or clinical trials for cancer chemoprevention. Phytochemicals of these types have great potential in the fight against human cancer, and a variety of delivery methods are available as a result of their occurrence in nature.

Botanicals in Cancer Chemoprevention

A multicentric hospital-based case-control study was simultaneously performed in a high-risk and a low-risk area for stomach cancer in Germany, 143 patients with incident stomach cancer and 579 controls completing a retrospective interview about life style aspects. Periods of non-centralized water supply or well water as the only source compared to life-long central water supply, and preservation of meat by smoking it with spruce compared to no home smoking of meat, were significantly associated with an increased stomach cancer risk. use of a refrigerator at home for 30 and more years compared to 24 years or less showed an inverse relationship, whereas salt intake estimated by questionnaire showed no relationship to stomach cancer risk. Tobacco smoking was negatively associated with risk for current smokers of cigarettes compared to non-smokers but was presumably not causally related. After adjustment for other food constituents, only increased vitamin C consumption showed an inverse relation to risk. For food groups, increased consumption of fruit, citrus fruit, cheese and whole-meal bread were associated with decreased risk. A similar effect was also seen for increased consumption of raw vegetables. Total vegetable consumption was not particularly associated with risk. Increased consumption of processed meat and of beer showed a positive association with risk whereas increased wine and liquor consumption showed a significant negative association. The association of alcoholic beverages with stomach cancer risk may reflect a particular life style rather than being causally related to risk.

H. Ostermeier

Papers

Case‐control study on stomach cancer in Germany