Compounds found in strawberries and blueberries associated with reduced risk of hypertension
Background Hypertension affects over one-third of US adults and is a major predisposing factor to cardiovascular disease. Although elevated blood pressure can be treated with drugs, lifestyle changes alone have been shown to improve hypertension. For instance, losing weight, lowering salt intake, and increasing consumption of certain dietary components (eg, fruit, vegetables, and calcium) are first-line recommendations for prevention and treatment of this disease. Among the many dietary constituents with promising effects on blood pressure regulation are the "flavonoids," a diverse and complex group of substances found mainly in fruit, vegetables, grains, and herbs. Having been shown to enhance immune and antioxidant functions, these compounds are often purported to be the "magic bullets" found in teas, juices, and red wine. However, the specific flavonoids associated with reduction of hypertension risk are less well understood. In response, British and US researchers recently investigated this question by using data from both the Nurses' Health and Health Professionals Follow-Up Studies. Their results can be found in the February 2011 issue of The American Journal of Clinical Nutrition.
Study Design A total of 133,914 women and 46,672 men, none of whom had hypertension, were followed for 14 y. During the study, subjects were asked to complete health questionnaires every 2 y, and dietary intake was assessed every 4 y. Incidence of newly diagnosed hypertension during the 14-y period was then related to consumption of various types of flavonoids.
Results During the investigation, 34,647 new cases of hypertension were reported by the study participants. Dietary information identified tea as the main contributor of flavonoids, with apples, orange juice, blueberries, red wine, and strawberries also providing important amounts. When the researchers looked at the relation between individual subclasses of flavonoids and hypertension, they found a strong inverse relation between the anthocyanins (found in blueberries, strawberries, blood oranges, eggplants, and other fruit and vegetables) and disease risk. Specifically, participants consuming the highest amounts of anthocyanins were 8% less likely to be diagnosed with hypertension than those consuming the lowest amounts (P < 0.03). This effect was even stronger in the younger (≤60 y) study participants and was related mostly to blueberry consumption, one of the two most commonly consumed sources of anthocyanins in the studies analyzed. Compared with people who did not eat blueberries, those who ate 1 serving/wk were 10% less likely to become hypertensive.
Conclusions The authors concluded that "anthocyanins may contribute to the prevention of hypertension" and speculated that this effect may be mediated via enhancement of nitric oxide activity within the blood vessel walls. However, controlled dietary intervention studies using rich sources of anthocyanins including blackcurrants, eggplants, blood oranges, and blueberries will be needed to validate this claim.
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