Berries Ward Off MI in Women
By Nancy Walsh, Staff Writer, MedPage Today
Women whose anthocyanin intake was in the highest quintile had a 32% decrease in risk of MI during 18 years of follow-up (HR 0.68, 95% CI 0.49 to 0.96, P=0.03), according to Eric B. Rimm, ScD, of Harvard University, and colleagues.
And in a food-based analysis, women who consumed more than three servings of strawberries or blueberries each week showed a trend towards a lower MI risk, with a 34% decrease (HR 0.66, 95% CI 0.40 to 1.08, P=0.09) compared with women who rarely included these fruits in their diet, the researchers reported online in Circulation.
"Growing evidence supports the beneficial effects of dietary flavonoids on endothelial function and blood pressure, suggesting that flavonoids might be more likely than other dietary factors to lower the risk of [coronary heart disease] in predominantly young women," they observed.
A number of preclinical experiments have demonstrated cardioprotective effects of anthocyanins, including anti-inflammatory effects, plaque stabilization, and inhibition of the expression of growth factors.
While studies have suggested that MI risk is increased in young and middle-age women who smoke or use oral contraceptives, little is known about the influence of diet in this population, whose risk may differ from that in older women.
The younger women may have a greater likelihood of endothelial dysfunction and coronary vasospasm and less obstructive disease.
Because dietary flavonoids -- found in vegetables, fruits, wine, and tea -- are recognized as benefiting endothelial function, the researchers looked at outcomes for 93,600 women enrolled in the Nurses' Health Study II who reported their consumption of various foods and their lifestyle factors every 4 years.
At the time of enrollment, beginning in 1991, participants were ages 25 to 42.
During almost 2 decades of follow-up, there were 405 cases of MI, occurring at a median age of 48.9 years.
Review of the food frequency and lifestyle questionnaires revealed that women who consumed high levels of anthocyanins were less likely to smoke, were more physically active, and had lower fat and higher fiber intake.
The 32% reduction in MI risk was seen after adjustment for multiple factors including body mass index, physical activity, saturated fat intake, use of caffeine and alcohol, and family history of MI.
"This inverse association was independent of established dietary and nondietary [cardiovascular disease] risk," the researchers noted.
Even adding conditions such as hypertension, dyslipidemia, and diabetes to the analytical model did not significantly change the risk estimate (HR 0.70, 95% CI 0.50 to 0.97).
Comparison of risk among women in the highest and lowest 10% of anthocyanin intake showed a relative risk of 0.53 (95% CI 0.33 to 0.86) for the high-intake group, which suggested the presence of a dose-response relationship.
Intake of other types of flavonoids did not significantly lower the risk of MI. The researchers had hypothesized that high intake of flavan-3-ol also would be important, because they had previously identified cardiovascular benefits for one type of flavan-3-ol compound in a meta-analysis.
The lack of effect in the current analysis may have reflected the fact that in the early 1990s, when the study began, most food frequency questionnaires did not include dark chocolate, which is a primary source for flavan-3-ol, they noted.
Adjustment for additional dietary factors such as total fruit and vegetable consumption also did not alter the risk, which suggests "that the benefits are specific to a food constituent in anthocyanin-rich foods (including blueberries, strawberries, eggplants, blackberries, blackcurrants) and not necessarily to nonspecific benefits among participants who consume high intakes of fruits and vegetables."
However, the results of this study do not support the use of flavonoid dietary supplements, according to Michael Rinaldi, MD, of the Carolinas HealthCare System's Sanger Heart and Vascular Institute in Charlotte, N.C.
The study does suggest that a healthy diet that includes fruits and vegetables can be healthy, said Rinaldi, who was not involved in the study.
"On the other hand, if you're going to say that these flavonoid substances in the berries should be taken as supplements, that's not what the study has the power to say," he told MedPage Today in an interview.
Limitations of the study included a lack of information about the results of cardiac catheterization and the possibility of additional unmeasured confounding factors.
In addition, while the model adjusted for intake of a number of other potentially beneficial food components, there may have been other unidentified compounds in fruits that contribute to cardioprotection.
"In a population-based study like ours, it is impossible to disentangle the relative influence of all the constituents of fruits and vegetables," the researchers wrote.
Further research will be needed to identify cardiac biomarkers that could help explain mechanisms of action, to explore dose responses, and to evaluate longer-term clinical endpoints.
The
study was funded by the National Institutes of Health, the Department
of Health and Human Services, and the U.K. Biotechnology and Biological
Sciences Research Council.
The authors reported no financial disclosures.
The authors reported no financial disclosures.
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