Citrus fruits are among foods, also including some vegetables, wine, chocolate and beans, that contain health-protective flavonoids. (Matthew Mead/Associated Press)

Increased consumption of flavonoid-rich foods such as certain citrus fruits may help reduce the risk of stroke in women, suggests a study by European and U.S. scientists.

For the study, published Thursday in Stroke, a journal of the American Heart Association, researchers analyzed the flavonoid intake of 69,622 women from the U.S.-based Nurses’ Health Study, which has followed nurses since 1976 to assess risk factors for cardiovascular disease and cancer.

"What our study was showing that specifically that these flavanones present almost exclusively in citrus fruits seem to be associated with a reduction in risk of stroke," Aedín Cassidy, the study's lead author and professor of nutrition at Norwich Medical School in the University of East Anglia in the United Kingdom, told CBC News.

The total flavonoid intake of the 69,622 women was calculated after they completed food intake questionnaires collected every four years using a U.S. Department of Agriculture database. During 14 years of followup surveys beginning in 1990, 1,803 incidents of strokes were confirmed from the women.

The research found that women who ate high amounts of citrus products, which contain a specific class of flavonoid called flavanones, had a 19 per cent lower risk of ischemic (blood clot-related) stroke than women who didn't consume as much.

Women with the lowest intake of flavonoids took in about 150 milligrams a day or less, compared to more than 470 mg a day by women consuming the highest level.

A piece of citrus fruit normally contains 45 to 50 mg of flavanones.

While previous studies have shown increased consumption of flavonoid-rich fruits and vegetables (preferably five servings a day) may help protect against stroke, researchers conducting the study released Thursday found most of the antioxidant-rich products consumed by the women with lower stroke risk were oranges, grapefruit and their juices.

The women with higher total flavonoid intake also tended to:

• Smoke less.
• Exercise more.
• Have greater intakes of fibre, folate, fruits and vegetables.
• Have lower intakes of caffeine and alcohol.

Cassidy said flavonoids are thought to provide protection against stroke through several mechanisms, including improving blood vessel function and having an anti-inflammatory effect.

The researchers warn that further studies, which may include randomized trials of citrus-based foods, are needed to confirm their findings.

Other researchers in the study, supported with grants from the U.S. National Institutes of Health, are from the United States and Italy. A couple of the researchers have received funding from pharmaceutical companies to conduct studies on flavonoid-rich foods in the past.