The findings of the new study, published in the current issue of the journal Cancer Epidemiology Biomarkers & Prevention, are based on dietary intakes of 88,759 women and 47,828 men, and show that people with a daily intake of six or more portions could reduce the risk of kidney cancer by 55 per cent, compared to those who ate less than three portions a day.
More than 80 per cent of all kidney cancers are accounted for by renal cell carcinoma (RCC). According to the charity Cancer Research UK, kidney cancer is the tenth most common form of the disease, with a male:female incidence ratio of 5:3. In the UK alone, around 6,600 new cases of kidney cancer are diagnosed each year, and the disease results in around 3,600 deaths.
Age, sex, obesity, smoking and several genetic and medical conditions are believed to be risk factors, but epidemiological data to support the role of diet in kidney cancer aetiology have yielded mixed results.
The researchers, from Harvard School of Public Health, Brigham and Women's Hospital, and Harvard Medical School, used data from the Nurses' Health Study (1980 to 2000) and the Health Professionals Follow-up Study (1986 to 2000), which collected dietary intakes using validated semi-quantitative food frequency questionnaires (FFQ) completed every two to four years.
Lead researcher Jung Eun Lee and colleagues prospectively investigated the link between renal cell cancer and dietary intakes of fruits, vegetables, vitamins A, C, and E, and carotenoids.
During the years of follow-up, the researchers documented 248 incident cases of renal cell cancer (132 women and 116 men).
Lee and co-workers report that men who regularly consumed six or more portions of fruit and vegetables per day were associated with a 55 per cent reduction in RCC risk, compared to those who consumed less than three portions per day.
No statistically significant association was observed for women at any level of fruit and vegetable consumption, they said.
"Intakes of vitamins A and C from food and carotenoids were inversely associated with the risk of renal cell cancer in men only, but we cannot exclude the possibility that this was due to other factors in fruit and vegetables," wrote the researchers.
On the other hand, no link between vitamin E and renal cell cancer risk in women was observed.
"Fruit and vegetable consumption may reduce the risk of renal cell cancer in men," concluded the researchers.
Intake of cruciferous vegetables has previously been linked to lower risks of certain cancers, including colon cancer, while increased carotenoid intake has been linked to lower risk of prostate cancer.
The "five-a-day" message is well known, but applying this does not seem to be filtering down into everyday life. Recent studies have indicated that consumers in both Europe and the US are failing to meet recommendations from the WHO to eat 400 grams of fruit and vegetables a day.
Source: Cancer Epidemiology Biomarkers & Prevention December 2006, Volume 15, Pages 2445-2452 "Intakes of Fruits, Vegetables, Vitamins A, C, and E, and Carotenoids and Risk of Renal Cell Cancer" Authors: J.E. Lee, E. Giovannucci, S.A. Smith-Warner, D. Spiegelman, W.C. Willett and G.. Curhan