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Blueberries every day keeps high blood pressure at bay

Blueberries may be a simple way to lower this important cardiovascular disease risk factor.

Study under review: Daily blueberry consumption improves blood pressure and arterial stiffness in post-menopausal women with pre- and stage 1-hypertension: A randomized, double-blind, placebo-controlled clinical trial

Introduction

Your heart beats around 100,000 times a day. As blood moves through your body, it exerts pressure on the veins and arteries. While blood pressure tends to increase with age[1] and can vary transiently based on physical activity[2] and consumption of substances like caffeine[3], a “healthy” resting blood pressure for adults is 120/80 ‘millimeters of mercury’ or mmHg. The top number, or systolic blood pressure, is the pressure in your blood vessels during heart contraction, whereas the bottom number, or diastolic blood pressure, is the pressure sustained while the heart is in the relaxed state.

Chronic high blood pressure is a risk factor for a number of disorders throughout the body, such as stroke[4], glaucoma[5] and retinopathy in the eye, heart attacks[4], heart failure[6], and kidney failure. In the U.S., it’s estimated that about 29% of adults have high blood pressure (greater than 140/90 mmHg) and roughly another third of adults have pre-hypertension (greater than 120/80 mmHg) and are at risk of developing high blood pressure. Two of the five most commonly prescribed drugs in the U.S. treat high blood pressure, with nearly 46 million Americans taking at least one drug for the condition.

Studies on blood pressure in older women are extremely important. While high blood pressure is more prevalent[7] in younger men than in younger women, by age 65 more women than men are affected. The goal of this study was to examine blueberry consumption in postmenopausal women at risk of developing hypertension to determine if blood pressure and arterial stiffness could be decreased.

As we get older, our arteries tend to get stiffer and less elastic. Since the arterial vascular tone plays a key role in maintaining adequate blood circulation, when elasticity is affected, an increased stress is placed on the heart. High blood pressure and arteriosclerosis, or hardened arteries, often go hand in hand. The most common type of arteriosclerosis is known as atherosclerosis, where fatty plaque deposits build up on the inner surfaces of hardened arteries. Arteriosclerosis is also linked[7] to increased risk of stroke, heart attacks, and kidney failure.

Blood pressure is measured with a sphygmomanometer, the cuff that health professionals put around your arm at each doctor’s visit. Arterial stiffness is a little trickier. One way to measure this non-invasively is called Pulse Wave Velocity (PWV). Imagine your arteries as a plastic tube, and the ‘wave’ of pressure caused by your heartbeat as a ball bouncing back and forth between the sides of the tube. If the plastic is very hard, the ball will bounce down the tube faster than if the plastic is soft - just like if your arteries are very stiff, the wave of blood pressure will move through the artery faster.

This can be quantified by placing pressure sensors at two different points in the body, and then measuring the time it takes for a blood pressure wave to travel between the two sensors. Since the distance between the two sensors is known, the travel time of the wave can be used to calculate the stiffness of the artery through which it traveled. The two most common PWV measurements are between the carotid artery in the neck and the femoral artery in the leg (cfPWV), and between the brachial artery in the upper arm and the anterior tibial artery in the ankle (baPWV). The cfPWF measurement is more relevant to the central arteries, while the baPWV is more relevant to the peripheral arteries. Increased arterial stiffness has been shown to be a risk factor[8] for cardiovascular disease and strokes.

High blood pressure and arterial stiffness have been linked to a number of disorders, including heart disease and stroke.

Why blueberries? Several[9] studies[10] have shown that blueberry consumption is linked to a modest decrease in blood pressure in various groups of people with hypertension. Blueberries contain a number of compounds, including anthocyanins (which put the “blue” in blueberry) and other flavonoids that act as antioxidants. Figure 1 shows some potential mechanisms by which anthocyanins may help with heart disease prevention. An especially important one may be that these compounds increase the production of nitric oxide, which acts as a vasodilator and lowers blood pressure. Since current recommendations[11] for pre-hypertension are to make dietary and lifestyle changes (e.g. decreasing sodium intake and increasing exercise) before turning to medication, evaluating blueberries in additional populations is an important area of research.

Figure 1: Mechanisms linking anthocyanins to heart disease prevention

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Other Articles in Issue #06 (April 2015)