HEALTH NEWS

Study Title:

Blueberries, Strawberries, and Reduced Heart Attack Risk

Study Abstract

Background—Our current knowledge of modifiable risk factors to prevent myocardial infarction (MI) in young and middle-aged women is limited, and the impact of diet is largely unknown. Dietary flavonoids exert potential beneficial effects on endothelial function in short-term trials; however, the relationship between habitual intake and risk of MI in women is unknown.

Methods and Results—We followed up 93 600 women 25 to 42 years of age from the Nurses’ Health Study (NHS) II who were healthy at baseline (1989) to examine the relationship between anthocyanins and other flavonoids and the risk of MI. Intake of flavonoid subclasses was calculated from validated food-frequency questionnaires collected every 4 years using an updated and extended US Department of Agriculture database. During 18 years of follow-up, 405 cases of MI were reported. An inverse association between higher intake of anthocyanins and risk of MI was observed (hazard ratio, 0.68; 95% confidence interval, 0.49–0.96; P=0.03, highest versus lowest quintiles) after multivariate adjustment. The addition of intermediate conditions, including history of hypertension, did not significantly attenuate the relationship (hazard ratio, 0.70; 95% confidence interval, 0.50–0.97; P=0.03). Combined intake of 2 anthocyanin-rich foods, blueberries and strawberries, tended to be associated with a decreased risk of MI (hazard ratio, 0.66; 95% confidence interval, 0.40–1.08) in a comparison of those consuming >3 servings a week and those with lower intake. Intakes of other flavonoid subclasses were not significantly associated with MI risk.

Conclusions—A high intake of anthocyanins may reduce MI risk in predominantly young women. Intervention trials are needed to further examine the health impact of increasing intakes of commonly consumed anthocyanin-rich foods.

From press release:

Young and middle-age women whose diet included high levels of anthocyanins -- the flavonoids present in red and blue fruits such as strawberries and blueberries -- had a significantly reduced risk for myocardial infarction (MI), a large prospective study found.

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."

Study Information

Aedín Cassidy, et al.
High Anthocyanin Intake Is Associated With a Reduced Risk of Myocardial Infarction in Young and Middle-Aged Women
Circulation
2013 January
Harvard School of Public Health,