"The findings of this large study provide support for an inverse association of selected classes of flavonoids with colorectal cancer risk," wrote lead author Marta Rossi in the August issue of Cancer Epidemiology Biomarkers and Prevention (Vol. 15, pp. 1555-1558), a journal of the American Association for Cancer Research.
Interest in flavonoids is growing rapidly and a mounting body of science, including epidemiological, laboratory-based and randomised clinical trials, continues to report the cancer-fighting potential of a number of different flavonoids, such as isoflavones, anthocyanidins and flavonols.
According to Business Insights, the market potential for flavonoids in the dietetic and nutritional supplement market is in excess of €670m ($862m) for 2007, with annual increases of 12 per cent.
The new case-control study, led by Rossi from the Università degli Studi di Milano, recruited 1,953 cases of colorectal cancers (1,225 colon cancers and 728 rectal cancers) and 4,154 hospital controls admitted for acute non-cancerous diseases. Dietary intake was assessed using validated food-frequency questionnaire (FFQ). Intake of six classes of flavonoids (isoflavones, anthocyanidins, flavones, flavonols, flavan-3-ols, and flavanones) was quantified using recently published food and beverage composition data.
After adjusting the results for sex, age, family history of colorectal cancer, BMI, energy intake, education, alcohol consumption, and physical activity, the researchers calculated that the highest intake of flavonols was associated with a 46 per cent reduction in the risk of colorectal cancer, compared to people in the lowest intake group.
Similar risk reductions were calculated for isoflavones (24 per cent), anthocyanidins (43 per cent), and flavones (22 per cent), when comparing highest intake to lowest intake.
No significant benefit of flavan-3-ols, flavanones, and total flavonoids was observed, said the researchers.
The study clearly has several limitations, namely the use of FFQs to quantify dietary intakes. Also, the study was not intended to identify the mechanism behind the benefits. Previous research has linked the protection to the antioxidant activity of the compounds, which reduce so-called oxidative stress and may protect against damage to DNA.
Further studies, including in vitro and in vivo tests, and mechanistic studies, as well as controlled, randomised clinical trials are need to follow to extend the study of such compounds to reduce the risk of colorectal cancer.
Nevertheless, the large study supports not only the potential anti-cancer activity of certain flavonoids, but highlights further the five-a-day message for a healthy, balanced diet rich in fruit and vegetables.
Flavones, commonly found in citrus fruit, have been increasingly linked to health benefits, including protection against cancer, heart disease and inflammation.
Berries, particularly blueberries, are a rich source of anthocyanidins (anthocyanins without the sugar part). A recent in vitro study reported that blueberry anthocyanidins, mainly delphinidin, cyaniding, petunidin, peonidin and malvidin, could stop the growth of liver cancer cells (Food Research International, Vol. 39, pp. 628-638).
There are 363,000 new cases of colorectal cancer every year in Europe, with an estimated 945,000 globally. About 492,000 deaths occur from the cancer each year. According to the European School of Oncology, 80 per cent of colorectal cancers may be preventable by dietary changes.
It is also one of the most curable cancers if diagnosis is made early.