Berry-Rich Diet Credited With One-Third Drop in MI Risk in NHS 2 Cohort

January 14, 2013

DALLAS, Texas — A diet rich in anthocyanins, a class of flavonoids with recognized heart-friendly antioxidant and anti-inflammatory effects, was associated with a 32% drop in the risk of incident MI in a cohort of >93 000 women from the Nurses' Health Study 2 (NHS 2) [1].

At the same time, there was similar drop in MI risk during the 18-year follow-up among those with the highest vs the lowest consumption level of blueberries and strawberries, a major source of anthocyanins in the US diet, NHS 2 investigators report in a study published online January 14, 2013 in Circulation.

The relationship between anthocyanin-rich foods and incident MI, write Dr Aedín Cassidy (University of East Anglia, Norwich, UK) and associates, was independent of clinical conditions related to MI risk, standard dietary and nondietary CV risk factors, other plant-based nutrients like potassium and folate, and total fruit and vegetable intake.

The findings, according to the group, suggest that the MI benefit stemmed from "a food constituent in anthocyanin-rich foods," which include blueberries, strawberries, eggplants, blackberries, and black currants, without necessarily reflecting the effects of an overall diet high in fruit and vegetables.

"These data are important from a public-health perspective because these fruits can be readily incorporated into the habitual diet," they write.

Diets Consistent With Current Recommendations

One of the study's conclusions--that a diet rich in blueberries and strawberries could help prevent MI--is the kind of message that tends to play well with the public, despite those conclusions being based on statistical associations in an observational study as well as making a leap between anthocyanin intake and berry intake.

"Bottom line, the study results confirm that people, in this case younger women, mean age 36 years, who consume diets consistent with current recommendations are at lower risk for myocardial infarction," commented Dr Alice H Lichtenstein (Cardiovascular Nutrition Laboratory, Tufts University, Boston, MA), who wasn't involved in the study, to heartwire . "It is important to keep in mind that the women who reported consuming more anthocyanin-rich foods--blueberries and strawberries--smoked less, were more physically active, had lower body weights, had less history of high plasma cholesterol concentrations and blood pressure, and habitually ate a healthier diet as suggested by less saturated and trans fat, more whole grains, [and] higher potassium and fiber indicative of higher vegetable and fruit intakes," Lichtenstein said. "Although the statistical models were corrected for these factors, they all covaried in the same direction."

Cassidy and some of her coauthors had previously reported that the highest levels of anthocyanin intake were associated with significantly reduced blood pressure in a combined analysis of cohorts from NHS 1 and 2 and the Health Professionals Follow-up Study. They found a similar relationship between intake of another flavonoid subclass, flavanones, in citrus fruit and reduced stroke risk in an NHS 1 cohort.

Risk-Factor Adjusted Analyses

The current study included 93 600 women in NHS 2 aged 25 to 42 years at baseline in 1989 who received food-frequency questionnaires every four years starting in 1991. Women with a history of cardiovascular disease, coronary revascularization, or most cancers had been excluded. Over a follow-up of 18 years, 405 incident MIs were recorded.

Following intake of a range of flavonoid subtypes common in the US diet, the group observed an inverse relationship (p for trend 0.047) between anthocyanin intake and MI risk.

The adjusted MI hazard ratio for the highest- vs the lowest-intake quintile was 0.68 (95% CI 0.49–0.96; p=0.03); every 15-mg increment in anthocyanin intake corresponded to a 17% drop in adjusted MI risk.

Covariates included body-mass index; activity levels; intake of caffeine, alcohol, cereal fiber, fat by saturated-fat subtypes, and aspirin; menopausal status; smoking; use of hormone replacement therapy or oral contraceptives; and MI family history.

The MI hazard ratio for the combined intake of blueberries and strawberries at more than three servings per week, compared with one or fewer servings per month, the group writes, was 0.66 (95% CI 0.40-1.08; p=0.09). Those berries accounted for 60% of anthocyanin intake in the analysis.

"So these data, as prior data, suggest that a healthier diet and physical-activity pattern is associated with better outcomes in terms of myocardial infarction," Lichtenstein said. "Caveat--topping a hot-fudge sundae with strawberries is unlikely to decrease anyone’s risk for myocardial infarction. When making changes to decrease the risk for myocardial infarction, one needs to think about the whole picture."

The authors had no disclosures; Lichtenstein previously disclosed that she has no conflicts.

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