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The Saga of Fruit/Vegetable Consumption and Cancer Risk
Abstract & Commentary
William B. Ershler, MD
Synopsis: In an analysis of a European cohort of approximately 400,000 individuals, among whom 30,000 cancers developed over nine years of follow-up, a very small inverse association between intake of total fruits and vegetables and cancer risk was observed.
Source: Boffetta P, et al. Fruit and vegetable intake and overall cancer risk in the European Prospective Investigation Into Cancer and Nutrition (EPIC). J Natl Cancer Inst. 2010;102:529-537.
It is a common notion that much cancer can be prevented by high intake of fruits and vegetables. The initial enthusiasm for such risk reduction was based upon early case-control studies, which were sufficient enough for the World Health Organization to formally recommend people to eat at least five portions (approximately 400 g) of fruits and vegetables daily.1 Subsequently, inconsistent results from many studies have not been able to conclusively establish an inverse association between fruit and vegetable intake and overall cancer risk. Prior to the current report, there had been six relatively large prospective studies examining this question.2-7 Of these, one showed that mortality was lower in both men and women when higher amounts of green and yellow vegetables and fruits were consumed;7 three studies reported a lower incidence of cancer in women who had high intakes of fruit and vegetables;2,3,5 and two showed no association between cancer risk and fruit or vegetable intake.4,6
To provide additional, substantial data on the relationships between total intake of fruits, total intake of vegetables, or total intake of both fruits and vegetables in combination and cancer risk, Boffetta and colleagues conducted an analysis of the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. Detailed information on the dietary habit and lifestyle variables of the cohort during the years 1992-2000 was obtained. Cancer incidence and mortality data were ascertained, and hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using multivariable Cox regression models. Analyses also were conducted for cancers associated with tobacco and alcohol after stratification for tobacco smoking and alcohol drinking.
Of the initial 142,605 men and 335,873 women from ten European countries included in the EPIC cohort, 9,604 men and 21,000 women were identified with cancer after a median follow-up of 8.7 years. The crude cancer incidence rates were 7.9 per 1,000 person years in men and 7.1 per 1,000 person years in women. Associations between reduced cancer risk and increased intake of total fruits and vegetables combined and total vegetables for the entire cohort were similar (200 g/d increased intake of fruits and vegetables combined, HR = 0.97, 95% CI = 0.96 to 0.99; 100 g/d increased intake of total vegetables, HR = 0.98, 95% CI = 0.97 to 0.99); intake of fruits showed a weaker inverse association (100 g/d increased intake of total fruits, HR = 0.99, 95% CI = 0.98 to 1.00). The reduced risk of cancer associated with high vegetable intake was restricted to women (HR = 0.98, 95% CI = 0.97 to 0.99). Stratification by alcohol intake suggested a stronger reduction in risk in heavy drinkers and was confined to cancers caused by smoking (cancers of the lung, kidney, upper respiratory and gastrointestinal tracts, liver, stomach, pancreas, and bladder) and alcohol (upper respiratory and gastrointestinal tracts, breast, liver, and colorectum).
During the 1980s and early 1990s, there emerged enthusiasm for the cancer-protective effects of fruits and vegetables, based primarily on case-control studies suggesting a substantial risk reduction among those who consumed high levels of fruits and vegetables. In fact, the World Health Organization recommended that people eat at least five portions (approximately 400 g) of fruits and vegetables daily.1 However, case-control studies have been prone to a number of biases, and when subjected to prospective analysis, a much smaller effect, if any, had been observed.2-7 The current study, by far the largest on the topic, demonstrated a very small inverse association between the intake of total fruits and vegetables and cancer risk. As noted, vegetable consumption alone conferred a modest benefit, but this was restricted to women, and consumption of fruits/vegetables by heavy drinkers had a small reduction in those cancers caused by smoking and drinking.
Willett, in an accompanying editorial,8 concludes that this study confirms that fruit and vegetable consumption, in general, has little or no effect on cancer risk, although the benefits, with regard to protection from cardiovascular disease, is more substantial. He also suggests that, whereas total fruit/vegetable consumption is of marginal value, certain individual dietary components may be of benefit and should be studied separately.
1. World Health Organization. Report of a WHO study group, diet, nutrition and the prevention of chronic diseases, Geneva, Switzerland: WHO;1990.
2. Benetou V, et al. Vegetables and fruits in relation to cancer risk: Evidence from the Greek EPIC cohort study. Cancer Epidemiol Biomarkers Prev. 2008;17:387-392.
3. Takachi R, et al. Fruit and vegetable intake and risk of total cancer and cardiovascular disease: Japan Public Health Center-Based Prospective Study. Am J Epidemiol. 2008;167:59-70. 4. Hung HC, et al. Fruit and vegetable intake and risk of major chronic disease. J Natl Cancer Inst. 2004;96:1577-1584.
5. Shibata A, et al. Intake of vegetables, fruits, beta-carotene, vitamin C and vitamin supplements and cancer incidence among the elderly: A prospective study. Br J Cancer. 1992;66:673-679.
6. George SM, et al. Fruit and vegetable intake and risk of cancer: A prospective cohort study. Am J Clin Nutr. 2009;89:347-353.
7. Sauvaget C, et al. Vegetables and fruit intake and cancer mortality in the Hiroshima/Nagasaki Life Span Study. Br J Cancer. 2003;88:689-694.
8. Willett WC. Fruits, vegetables, and cancer prevention: turmoil in the produce section. J Natl Cancer Inst. 2010;102:510-511.