Epidemiological and animal studies have shown that diets high in cruciferous vegetables result in less instances of certain cancers, especially lung, colon, breast and ovarian cancer, while the new study suggests the veggies may also benefit prostates.
Writing in the Journal of the National Cancer Institute , researchers from Canada and the US report that an increased intake of cruciferous vegetables was associated with a 40 per cent reduction in prostate cancer risk, with broccoli and cauliflower singled out as offering most protection.
"High intake of cruciferous vegetables, including broccoli and cauliflower, may be associated with reduced risk of aggressive prostate cancer," wrote lead author Victoria Kirsh from Cancer Care Ontario.
Over half a million news cases of prostate cancer are diagnosed every year world wide, and the cancer is the direct cause of over 200,000 deaths.
More worryingly, the incidence of the disease is increasing with a rise of 1.7 per cent over 15 years.
The new study, a prospective study of 1338 men taking part in a long-term randomised screening trial (29361 men in total), analysed dietary intakes using a 137-item food frequency questionnaire and followed the men for an average of 4.2 years.
Kirsh and co-workers report that increased intake of cruciferous vegetables was associated with a 40 per cent reduction in prostate cancer risk, with more than one serving of broccoli per week associated with a 45 per cent risk reduction, compared to less than one broccoli serving per month.
Increased consumption of cauliflower was also associated with a significant reduction of prostate cancer, with more than one serving of broccoli per week associated with a 52 per cent risk reduction, compared to less than one broccoli serving per month.
While no overall association was reported for vegetable consumption for overall prostate cancer risk, a significant risk reduction was reported for stage III and IV tumours.
A protective trend was also observed for increasing spinach consumption, but not statistically significant.
The researchers note that the study is limited by the fact that people with regular and high intake of fruit and vegetables tend to lead healthier lifestyles with more exercise, and lower smoking rates.
The cancer-fighting properties of broccoli, a member of the crucifer family of vegetables, are not new and previous studies have related these benefits to the high levels of active plant chemicals called glucosinolates.
These are metabolised by the body into isothiocynates, and evidence suggests these are powerful anti-carcinogens.
The main isothiocynate from broccoli is sulforaphane.
Some broccoli-extracts are currently available on the market, such as Cyvex's Nutrition's BroccoPlus, combines six per cent glucosinolates with sulforaphane, delivering high doses of these compounds in powder form, and B&D Nutritional Ingredients' sgs-100, a broccoli seed extract from a plant strain that is reported to be unusually high in sulforaphane glucisinolate (SGS).
The other researchers were affiliated with Yale University School of Medicine, Fred Hutchinson Cancer Research Center (Seattle), University of Washington, National Cancer Institute (National Institutes of Health), Department of Health and Human Services, and the Josephine Ford Cancer Center (Detroit).
Source: Journal of the National Cancer Institute Published on-line ahead of print, doi:10.1093/jnci/djm065 "Prospective Study of Fruit and Vegetable Intake and Risk of Prostate Cancer" Authors: V.A. Kirsh, U. Peters, S.T. Mayne, A.F. Subar, N. Chatterjee, C.C. Johnson, R.B. Hayes on behalf of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial