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Eat more blueberries and chocolate!

Comment by Paul Leeson, EACPR Exercise Basic and Translational Research Section

Habitual intake of flavonoid subclasses and incident hypertension in adults
Aedín Cassidy, Éilis J O'Reilly, Colin Kay et al
Am J Clin Nutr November 2010 ajcn.006783

Dietary intake of bioactive substances that lower blood pressure provides a simple and attractive way for patients to take day-to-day control of their health. Flavonoids are a group of bioactive plant-based substances that have become of interesting interest. In experimental studies they have direct effects on vascular biology, in particular nitric oxide bioavailability, which is likely to explain why they lower blood pressure in clinical studies. However, meta-analysis of randomised controlled trials of flavonoids demonstrates that not all subclasses of flavonoids lower blood pressure. Furthermore, the doses of flavonoids in some trials can not reasonably be achieved with simple dietary advice. So, which flavonoids work and how do people normally eat them in their diet?

Cassidy et al (Am J Clin Nutr 2011;93:338-347) recently addressed these questions using population-based data on diet and incidence of hypertension collected within the two Nurses’ Health Studies and the Health Professionals Follow-Up Study in the United States. They estimated flavonoid intake based on expected flavonoid content of the different foods that participants reported eating. They then related incidence of hypertension to intake of the major flavonoid subclasses. The biggest effect on blood pressure was seen with anthocyanin intake. Those with anthocyanin intake above the top quintile had an 8% decreased risk of hypertension (RR 0.92) compared to those below the bottom quintile for intake. The association was greater in those below 60yrs of age (RR 0.88). No other subclasses of flavonoid associated with risk of hypertension although some specific flavonoids within the subclasses did, namely, apigenin (5% reduction) as well as catechin and epicatechin (7% and 5% reduction respectively).

Which foods contained these flavonoids? The major sources of anthocyanins in the studies were blueberries and strawberries. Consumption of one or more servings of blueberries per week was associated with a 10% reduction in hypertension. Interestingly, however, there may be some complications to the story as a similar effect was not seen with strawberry consumption. As for catechin and epicatechin, these are the main constituents of dark cocoa. Therefore, if you have advised a patient to "eat more fruit and vegetables" but they still want more specific dietary advice about how to prevent hypertension try…. "eat more blueberries and chocolate’".