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Diets rich in fruits and vegetables have been linked with lower stroke risk in other studies, but researchers weren't sure why. For this study, they zeroed in on compounds called flavanones present in citrus fruits and found a winner.
"These data provide strong support for consuming more citrus fruits as part of your daily fruit and vegetable intake" to reduce the risk of ischemic [blood clot-related] stroke, said study leader Aedin Cassidy, head of nutrition at Norwich Medical School at the University of East Anglia in England.
It's possible that the flavanones in citrus fruits improve blood vessel function or reduce inflammation, which has been linked with stroke, the researchers said.
For maximum benefit, whole fruits are preferable to juice because they contain more flavanones and no added sugar, said Cassidy. The study, published online in the journal Stroke, was funded by the US National Institutes of Health.
Flavanones are a type of dietary flavonoid already associated with lower stroke risk. Besides fruits and vegetables, flavonoids are found in red wine and dark chocolate.
For this study, the researchers focused on six subclasses of flavonoids, including flavanones, to tease out the specific plant foods that help reduce stroke risk.
Evaluation of follow-up data
The researchers evaluated 14 years of follow-up data from the US Nurses' Health Study. The new research involved nearly 70,000 women who reported their food intake every four years and included details on fruit and vegetable consumption.
During the follow-up, 1,803 strokes occurred. About half were blood clot-related, the study authors noted.
Total flavonoid intake did not reduce stroke risk, but intake of flavanones did, the researchers said. Women who ate the most flavanones had a 19% lower risk of blood-clot related stroke than those who ate the least.
The investigators found that 95% of the flavanones consumed came from citrus fruit and juice, mostly orange and grapefruit. Those consuming the most citrus fruits and juice had a 10% reduced risk of stroke compared with those eating none, Cassidy said.
Vitamin C, previously suggested as the source of the cardio-protective effects, was not associated with lower stroke risk in this study.
Women with the lowest intake of flavanones took in about 150 milligramme a day of flavonoids or less, compared to more than 470 milligramme a day in the highest group.
A typical piece of citrus fruit contains 45 to 50 milligramme of flavanones, Cassidy said.
Flavonoids consumption
The study authors pointed out that those who ate the most flavonoids also smoked less and exercised more. They ate more fibre, vegetables and fruit overall and consumed less caffeine and alcohol.
While the study uncovered an association between flavanone consumption and reduced stroke risk, it did not prove a cause-and-effect relationship. Additional research is needed to better understand the association between flavanone consumption and stroke risk, the authors said. While this study only included women, Cassidy suspects the findings would apply to men. "These studies now need to be done," Cassidy said.
Hannah Gardener, an epidemiologist at the University of Miami Miller School of Medicine department of neurology, said the study adds valuable information to what is known about diet and stroke risk.
Eating fruit and vegetable
"There are several studies that have shown that greater consumption of fruits and vegetables has been linked with reduced risk of stroke," said Gardener, who was not involved in the study. What the new research adds is the focus on the subclasses of flavonoids, she said.
The bottom line? "It underscores the importance of fruit and vegetable intake," Gardener said. And it "provides evidence that citrus fruits in particular may be important in terms of reducing stroke risk."
The US Dietary Guidelines of America 2010 suggest filling half your plate with fruits and vegetables. Cassidy and a co-author report receiving funding from Unilever Research and GlaxoSmithKline to conduct trials and studies on flavonoid-rich foods in the past.
(Kathleen Doheny, HealthDay, February 2012)
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