Red and Blue Berries and Vegetables May Prevent Hypertension

January 19, 2011

January 19, 2011 (Norwich, United Kingdom)— Fruits and vegetables that are rich in anthocyanins--such as blueberries, strawberries, and blood oranges--may help prevent the development of hypertension, new research suggests [1].

Dr Aedín Cassidy (University of East Anglia, Norwich, UK) and colleagues analyzed data from the US Nurses' Health Studies (NHS I and II) and the Health Professionals Follow-up Study (HPFS), the first large study to investigate the effect of different flavonoids on the development of hypertension. They report their findings online November 24, 2010 in the American Journal of Clinical Nutrition.

"There are thousands of these flavonoid compounds and six subclasses of particular interest to human health," Cassidy explained to heartwire, adding thatflavonoids present in tea, fruit juice, red wine, and dark chocolate are already known to reduce the risk of cardiovascular disease.

She and her colleagues found that blood pressure was reduced by 8% in those with the highest intake of anthocyanins--one of these six subclasses --compared with those with the lowest intake.

There isn't anything special about blueberries. If people had eaten other foods with red or blue pigments . . . we would have seen the same effects.

Blueberries are a rich source of anthocyanins, and consumption of this food was associated with a 10% reduction in blood pressure, but "there isn't anything special about blueberries," she says; they just happen to play a large part in the American diet. "If people had eaten other foods with red or blue pigments that contain anthocyanins, such as black currants, raspberries, or aubergines [eggplants], we would have seen the same effects.

"In terms of guidance to patients, I think this can help us give a little bit more targeted advice. Rather than just telling them to eat more fruit and vegetables--which they are tired of hearing--we can try to refine messages about which dietary components are beneficial in terms of cardioprotective effects," she says. She cautions, however, that these findings come from an observational study and so will require confirmation in interventional trials.

Benefits of Anthocyanins Greatest in Those Under 60

Cassidy and colleagues had 14 years of follow-up data on almost 134 000 women from the NHS I and II and 23 000 men from the HPFS, which allowed them "to capture habitual intake," she notes. The subjects, who did not have hypertension at baseline, were asked to complete health questionnaires every two years, and their dietary intake was assessed every four years through a food frequency questionnaire.

"We looked at the cumulative averages of intake of various different flavonoids to give us a reasonable estimate of consumption, which was then related to the incidence of newly diagnosed hypertension during the 14-year period," Cassidy explained.

There were 29 018 cases of hypertension in women and 5629 cases among men. In pooled multivariate-adjusted analyses, participants in the highest quintile of anthocyanin intake--around one serving per week, in this case predominantly from blueberries and strawberries--had an 8% relative reduction in risk (RR 0.92; p<0.03) of hypertension compared with those in the lowest quintile of intake.

The effects of anthocyanin intake appeared to be greatest in those under the age of 60, says Cassidy, with a 12% relative reduction in risk of hypertension in the highest vs lowest quintile for intake in this age group (RR 0.88; p<0.001). "We think the greater effect in younger people is because diet is a preventive thing," she says, adding that "cumulative damage over many years might exceed the capacity for flavonoids to have beneficial effects in older people.

"Our findings are exciting and suggest that an achievable dietary intake of anthocyanins may contribute to the prevention of hypertension," she notes, adding that the antihypertensive bioactivity of compounds such as anthocyanins could be related to vasodilatory processes.

The next stage of the research will be to conduct randomized controlled trials with different dietary sources of anthocyanins to define the optimal dose and sources for hypertension prevention, enabling the development of targeted public-health recommendations on how to reduce blood pressure, she concludes.

Cassidy has received funding from Unilever Research and GlaxoSmithKline to conduct trials and experimental (in vitro) studies on flavonoid-rich foods. Disclosures for the coauthors are listed in the paper.

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