The study findings – presented at the International Conference on Frontiers in Cancer Prevention Research – could mean people who consume high levels of the flavonoid compounds linked to the benefits have much lower risks of developing aggressive forms of prostate cancer.
Led by Susan Steck, from the Arnold School of Public Health, USA, the researchers found that men with the highest total intake of flavonoids had a 25% lower risk of aggressive prostate cancer than those with the lowest risk.
"Incorporating more plant-based foods and beverages, such as fruits, vegetables, herbs and tea, into the diet may offer some protection against aggressive prostate cancer," said Steck.
"Filling your plate with flavonoid-rich foods is one behaviour that can be changed to have a beneficial impact on health," she said.
Previous research has suggested that flavonoids may have beneficial effects against prostate cancer cells in a laboratory; however, the authors noted that very few studies have examined the effect of flavonoids on prostate cancer in humans.
Steck and her colleagues analysed data from 920 African-American men and 977 white men who were newly diagnosed with prostate cancer, and taking part in the North Carolina-Louisiana Prostate Cancer Project. All the men completed a self-reported dietary history questionnaire to assess flavonoid intake – which was measured using the U.S. Department of Agriculture's 2011 Database for the Flavonoid Content of Selected Foods.
Men with the highest total intake of flavonoids were found to have a 25% lower risk for aggressive prostate cancer compared with those men with the lowest flavonoid intake.
Dietary questionnaire results revealed that citrus fruits and juices, such as oranges and grapefruits, tea, grapes, strawberries, onions and cooked greens were the top contributors to total flavonoid intake among the participants.
"We found that higher total flavonoid intake was associated with reduced odds for aggressive prostate cancer in both African-American and European-American men, but no individual subclass of flavonoids appeared to be protective independently, suggesting that it is important to consume a variety of plant-based foods in the diet, rather than to focus on one specific type of flavonoid or flavonoid-rich food," said Steck.
"In particular, consuming more flavonoid-rich foods may be beneficial for those people who are at increased risk for cancer, such as smokers," she added.