Some very heartening signs from a large study further boost berries' healthy reputation.
The new analysis found that young and middle-aged women who ate three or more servings of blueberries and/or strawberries per week cut their heart attack risk by one-third.
The same risk reduction was seen in women whose diets were rich in other food sources of the kinds of pigments found in those berries – anthocyanins, which belong to the family of antioxidants known as flavonoids.
This was an epidemiological study, in which scientists look for statistical links between lifestyle factors and disease rates.
Unlike controlled clinical trials, an epidemiological study can only show correlations between diet and disease.
However, the new study's findings enjoy support from similar ones – as well as a few clinical trials – and they fit with the known effects of berries (and cherries) on people's “working” genes.
Why would berries help deter heart attacks?
Most disease and aging processes – including cardiovascular disease and resulting heart attacks – are initiated or promoted by chronic, silent inflammation.
Chronic inflammation generates free radicals, which oxidize and damage cell membranes and blood cholesterol.
Worse, those inflammation-generated free radicals activate gene switches that produce more inflammation and free radicals.
The compounds that make berries, cocoa, and tea exceptionally healthful are called flavonoids ... which belong to a large family of beneficial compounds called polyphenols.
Polyphenols promote the “expression” of genes that moderate inflammation and stimulate the body's own antioxidant network. (See “Berries, cocoa, and brethren influence genes beneficially”, below.)
This applies to the primary flavonoid-type polyphenols in berries, called anthocyanins, which also give berries their blue-red colors.
Berries seen to cut women's heart attack risk
The new, very large study was conducted by a team from the Harvard School of Public Health and the UK's University of East Anglia (Cassidy A et al. 2013).
The scientists conducted a “prospective” study among 93,600 women aged 25 to 42 who were registered with the Nurses' Health Study II.
Starting in 1989, the female nurses completed questionnaires about their diet every four years, for 18 years.
The Harvard-UK team found that – compared to women who ate blueberries and/or strawberries once a month or less – the women who ate the most blueberries and strawberries were 32 percent less like to have suffered a heart attack.
The findings applied even to women who reported eating diets rich in other fruits and vegetables, which are known to aid heart health ... meaning that the berries added extra benefit.
And the finding held true after the researchers adjusted the analysis to account for other risk factors, such as age, high blood pressure, family history of heart attack, body mass, exercise, smoking, and caffeine or alcohol intake.
“We have shown that even at an early age, eating more of these fruits may reduce risk of a heart attack later in life,” said lead author Aedín Cassidy, Ph.D., of the University of East Anglia (AHA 2013).
The authors wrote that the anthocyanins in berries probably reduce heart risk because they help dilate arteries, counter the buildup of plaque, and provide other cardiovascular benefits.
Earlier this year, the same Harvard-UK team linked diets similarly high in blueberries or other anthocyanin-rich fruits to a one-third percent lower risk of diabetes in men and women.
“Blueberries and strawberries can easily be incorporated into what women eat every week,” said co-author Eric Rimm D.Sc., of the Harvard School of Public Health. “This simple dietary change could have a significant impact on prevention efforts.” (AHA 2013)
Berries, cocoa, and brethren influence genes beneficially
Blueberries and strawberries were the focus of the analysis because they are the most commonly eaten berries in the United States.
As the researchers said, it's likely that all foods rich in anthocyanins and/or other polyphenols also provide protection, by helping to deter the damage caused by inflammation and free radicals.
It's becoming clear that polyphenols generally do not exert direct antioxidant effects in the body… at least not to a very substantial extent.
Instead, polyphenols appear to exert strong indirect effects on oxidation and inflammation via so-called “nutrigenomic” effects on gene switches (e.g., transcription factors) in our cells.
Polyphenols' nutrigenomic effects tend to moderate inflammation and stimulate the body's own antioxidant network … which includes enzymes, lipoic acid, CoQ10, melatonin, and vitamins C and E.
The richest known food source of polyphenols are raw (non-alkalized / non-“Dutched”) cocoa, berries, plums, prunes, tea, coffee, extra virgin olive oil, beans, and whole grains.
Beneficial procyanidin-type polyphenols abound in cocoa, dark-hued berries – e.g., blackberries, blueberries açaí berries – grapes, red wine, red cabbage, and tea. And beneficial anthocyanin-type polyphenols abound in cherries and berries.
Extra virgin olive oil is uniquely rich in hydroxytyrosol, oleuropein, and other tyrosol esters … particularly potent polyphenols with clinically documented vascular benefits.
According to USDA data, the average American's diet provides about 852mg of polyphenols daily … with most Americans getting most of them coming from coffee.
American Heart Association (AHA). Strawberries, blueberries may cut heart attack risk in women. January 14, 2013. Accessed at http://newsroom.heart.org/news/strawberries-blueberries-may-cut-heart-attack-risk-in-women
Cassidy A, Mukamal KJ, Liu L, Franz M, Eliassen AH, Rimm EB. High anthocyanin intake is associated with a reduced risk of myocardial infarction in young and middle-aged women. Circulation. 2013 Jan 15;127(2):188-96. doi: 10.1161/CIRCULATIONAHA.112.122408. Accessed at http://circ.ahajournals.org/content/127/2/188.abstract
Cassidy A, O'Reilly ÉJ, Kay C, Sampson L, Franz M, Forman JP, Curhan G, Rimm EB. Habitual intake of flavonoid subclasses and incident hypertension in adults. Am J Clin Nutr. 2011 Feb;93(2):338-47. doi: 10.3945/ajcn.110.006783. Epub 2010 Nov 24.
Joshipura KJ, Hung HC, Li TY, Hu FB, Rimm EB, Stampfer MJ, Colditz G, Willett WC. Intakes of fruits, vegetables and carbohydrate and the risk of CVD. Public Health Nutr. 2009 Jan;12(1):115-21. doi: 10.1017/S1368980008002036. Epub 2008 Apr 15.
Wedick NM, Pan A, Cassidy A, Rimm EB, Sampson L, Rosner B, Willett W, Hu FB, Sun Q, van Dam RM. Dietary flavonoid intakes and risk of type 2 diabetes in US men and women. Am J Clin Nutr. 2012 Apr;95(4):925-33. doi: 10.3945/ajcn.111.028894. Epub 2012 Feb 22.