Onion compound may protect colon from cancer: Study
However, dietary intakes of the compound were not associated with beneficial effects on rectal health, researchers report in the British Journal of Nutrition.
Researchers from the University of Aberdeen, Ireland's National Cancer Registry Ireland and the University of Ottawa add that increased intakes of flavonols in general were associated with a 40 per cent reduction in the risk of dev eloping colorectal cancer.
Flavonoids can be split into a number of sub-classes, including anthocyanins found in berries, flavonols from a variety of fruit and vegetables, flavones from parsley and thyme, for example, flavanones from citrus, isoflavones from soy, mono- and poly-meric flavonols like the catechins in tea, and proanthocyanidins from berries, wine and chocolate.
A vast body of epidemiological studies has linked increased dietary intake of antioxidants from fruits, vegetables wine, chocolate, coffee, tea, and other foods to reduced risks of a range of diseases including cancer, cardiovascular disease and diabetes.
In order to examine the benefits of a flavonoid-rich diet with respect to colorectal cancer risk, the researchers performed a case-control study involving 264 people with confirmed colorectal cancer and 408 healthy, cancer-free controls.
Colorectal cancer accounts for nine per cent of new cancer cases every year worldwide. The highest incidence rates are in the developed world, while Asia and Africa have the lowest incidence rates.
Since tea if the main dietary source of flavonoids in the UK, the researchers sought to distinguish between total dietary and non-tea intake of four flavonoid subclasses - flavonol, procyanidin, flavon-3-ol, and flavanone.
The participants were drawn from a “tea-drinking population with a high colorectal cancer incidence”, said the researchers, led by Janet Kyle.
While no association between total dietary flavonoids and the incidence of colorectal cancer was observed, when Kyle and her co-workers considered only flavonoids from non-tea sources and the specific site of the cancer, a significant protective effect was documented for non-tea flavonols and colon, but not rectal, cancer.
“We concluded that flavonols, specifically quercetin, obtained from non-tea components of the diet may be linked with reduced risk of developing colon cancer,” concluded the researchers.
The researchers did not study the mechanism behind the potential beneficial effects, but an earlier study from UCLA (Cancer, 2008, Vol. 112, pp. 2241-2248) suggested that flavonoids may act by blocking the formation of blood vessels that tumours develop so they can grow and spread, a process called angiogenesis. A potential role in apoptosis, or naturally programmed cell death, may also be occurring.
Source: British Journal of Nutrition
Published online ahead of print, First View article, doi:10.1017/S0007114509991784
“Dietary flavonoid intake and colorectal cancer: a case-control study”
Authors: J.A.M. Kyle, L. Sharp, J. Little, G.G. Duthie, G. McNeill