A large study of over 400,000 people living in ten western European countries found only a modest link between high intake of fruit and vegetables and reduction in overall cancer risk: thus failing to confirm the widely held belief enshrined in the World Health Organization’s recommendation that people should eat five servings of fruit and vegetables a day to prevent cancer and other diseases.

Dr Paolo Boffetta, of the Mount Sinai School of Medicine in New York, and colleagues, wrote about their findings in a study published in the 6 April online issue of the Journal of the National Cancer Institute.

In 1990 the World Health Organization recommended people eat five helpings of fruit and vegetables a day to reduce their risk of cancer, cardiovascular and other diseases. But since then, many studies have either produced inconsistent results or failed to find a significant link between fruit and vegetable intake and cancer risk, wrote the authors.

For their prospective study, Boffetta and colleagues analyzed data from the European Prospective Investigation into Cancer and Nutrition (EPIC), which recruited 142,605 men and 335,873 women in Denmark, France, Germany, Greece, Italy, the Netherlands, Norway, Spain, Sweden and the United Kingdom, between 1992 and 2000.

The data was mostly self-reported by the participants and detailed their dietary and lifestyle habits. The participants were followed for a median of 8.7 years, during which time deaths and incidents of cancer diagnoses were noted.

The researchers then analysed the data using Cox regression analysis to find links between diet, lifestyle and cancer risk. Their results showed:

  • 9,604 men and 21,000 women received a cancer diagnosis (out of 142,605 men and 335,873 women initially included in the study).
  • A “crude” (ie unadjusted) cancer incidence rate of 7.9 per 1000 person-years in men and 7.1 per 1000 person-years in women.
  • A modest reduced risk of cancer risk linked to increased intake of total fruit and vegetables (3 per cent), increased vegetable intake (2 per cent, but this was restricted to women only), and increased fruit intake (1 per cent).
  • Heavy drinkers who consumed higher amounts of fruits and vegetables showed stronger reductions, but this was confined to cancers related to smoking and alcohol.

The authors concluded that:

“A very small inverse association between intake of total fruits and vegetables and cancer risk was observed in this study. Given the small magnitude of the observed associations, caution should be applied in their interpretation.”

The researchers also noted that participants who ate more fruits and vegetables also tended to consume less alcohol, either never smoked or only for a short time, and were physically more active, and these lifestyle factors could have equally contributed to lower cancer risk.

In an accompanying editorial, Dr Walter C. Willett, Chair, Department of Nutrition Fredrick John Stare Professor of Epidemiology and Nutrition at the the Harvard School of Public Health, noted that the study “strongly confirms” the findings of other prospective studies (these follow people over a period of time, but do not compare a treatment group to a control group like they do in clinical trials), that eating more fruit and vegetables has little or no effect on reducing people’s risk of cancer, although it does appear to reduce their risk of cardiovascular disease.

This could be because the study only looked at all fruits and vegetables and all cancers, and Willett suggests that future studies concentrate on the effect of specific types of fruit and vegetables, perhaps on specific cancers, and starting at earlier periods of people’s lives.

Experts commenting on the study might argue that while 2 or 3 per cent reduced risk may not seem very significant to individuals, in public health terms it translates to thousands of people not getting cancer by eating more fruit and vegetables.

Another, perhaps more indirect argument, is that since we already know that obesity increases cancer risk, then the more fruit and vegetables we eat, the less chance we have of becoming obese and getting cancer that way because they would displace higher calorie foods in our diet.

“Fruit and Vegetable Intake and Overall Cancer Risk in the European Prospective Investigation Into Cancer and Nutrition (EPIC).”
Paolo Boffetta, Elisabeth Couto, Janine Wichmann, Pietro Ferrari, Dimitrios Trichopoulos, H. Bas Bueno-de-Mesquita, Fränzel J. B. van Duijnhoven, Frederike L. Büchner, Tim Key, Heiner Boeing, et al
J Natl Cancer Inst, Advance Access published on April 6, 2010

Source: Oxford Journals, National Cancer Institute.

Written by: Catharine Paddock, PhD