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If you’re worried about high blood pressure, a new systematic review of scientific evidence has good news: Changing your diet really can make a difference. Not surprisingly, the most effective diet for reducing hypertension was one designed specifically for that purpose – the Dietary Approaches to Stop Hypertension (DASH) plan. But other interventions, including cutting salt and calories, also were associated with blood-pressure benefits.
“Many ‘healthy’ diets have common elements, whether they are a named diet such as DASH, or not,” says Alice H. Lichtenstein, DSc, director of Tufts Cardiovascular Nutrition Laboratory and executive editor of the Health & Nutrition Letter. “Common elements include cutting calories, decreasing salt and refined carbohydrates, increasing fruits and vegetables, and focusing on healthy fats. To get the most benefit from any diet, the critical element is making small but sustainable – and, if necessary, incremental changes – to ensure long-term benefits.”
REVIEWING THE EVIDENCE: The new meta-analysis, published in the journal Hypertension, looked at data from 24 randomized controlled trials with a total of 23,858 participants conducted over the past 25 years. Such studies are considered the “gold standard” of scientific research and are designed to elicit cause and effect.
Overall, the net effect of dietary interventions averaged reductions of 3.07 mmHg for systolic pressure (the top number in a blood-pressure reading) and 1.81 mmHg for diastolic pressure (the bottom number). The DASH diet produced the largest improvements in blood pressure: minus 7.62 mmHg for systolic pressure and minus 4.22 mmHg for diastolic pressure. Low-sodium, low-sodium/high-potassium, low-sodium/low-calorie and low-calorie diets were all also associated with reductions in both systolic and diastolic pressure. Participants on a Mediterranean diet saw only a small reduction in diastolic blood pressure (-1.44 mmHg).
Dietary interventions were more effective for people with pre-existing hypertension and those who were not already taking medication for high blood pressure.
“As with any treatment,” Tufts’ Lichtenstein adds, “some people will reap greater benefit than others, particularly for blood pressure where we know responsiveness to dietary modification is highly variable. We can’t predict who those people will be ahead of time. Given that the characteristics of a diet good for blood-pressure lowering will have general benefits in other areas, we should all strive to achieve them.”
IMPORTANCE OF CONTROL: The numbers when you get your blood pressure checked represent the amount of force pushing against your artery walls when the heart is contracting (systolic) and when the heart is at rest (diastolic). When pressure rises in the vessels, the heart has to work harder and the arteries have to stretch more. Over time, high blood pressure damages the artery walls, making them more vulnerable to damage and prone to plaque buildup (atherosclerosis).
Since hypertension increases the workload on the heart, it can eventually damage those muscles and valves and cause heart failure, in which the heart can no longer keep up with the body’s demands. High blood pressure puts you at greater risk of heart attack, heart disease and aortic dissection (tearing in the heart).
This type of damage to the arteries can also affect the brain, and high blood pressure is a leading cause of stroke. High blood pressure is also associated with a greater risk of dementia.
Other risks from uncontrolled hypertension include kidney damage, vision loss, erectile dysfunction, fluid in the lungs, angina (chest pain) and peripheral artery disease. But these are effects, not symptoms- uncontrolled high blood pressure is sometimes called “the silent killer” because it has no symptoms. Until a doctor diagnoses hypertension, you may not be aware that it’s damaging your arteries, heart and other organs. It’s estimated that of all people with high blood pressure, more than 20% are unaware of their condition.
DASH DETAILS: The DASH eating plan shown to be effective against hypertension requires no special foods; it shares common elements with most “healthy” diet plans. Built on daily and weekly nutritional goals (see box), the DASH plan recommends:
– Eating vegetables, fruits and whole grains.
– Including fat-free or low-fat dairy products, fish, poultry, beans, nuts and vegetable oils.
– Limiting foods that are high in saturated fat, such as fatty meats, full-fat dairy products, and tropical oils such as coconut, palm kernel and palm oils.
– Limiting sugar-sweetened beverages and sweets.
When following the DASH eating plan, it is important to choose foods that are:
– Low in saturated and trans fats, replacing these fats with those high in monounsaturated and polyunsaturated fats.
– Rich in potassium, calcium, magnesium, fiber and protein.
– Lower in sodium.
To learn more about the DASH plan, see <www.nhlbi.nih.gov/health/health-topics/topics/dash>.
LIFESTYLE CHANGES: The American Heart Association <www.heart.org> recommends seven main ways you can help control your blood pressure through smart lifestyle choices:
1. Eat a better diet. The advice includes eating a diet rich in: fruits; vegetables; whole-grain, high-fiber foods; fat-free and low-fat or 1% dairy products; beans; skinless poultry and lean meats; fish, especially fatty fish containing omega-3 fatty acids, such as salmon, trout and herring (at least twice a week). Your diet should be low in saturated and trans fats (replacing these fats with monounsaturated and polyunsaturated fats) and sodium, and you should limit added sugars.
2. Enjoy regular physical activity.
3. Achieve and maintain a healthy weight.
4. Manage stress.
5. Avoid tobacco products.
6. Comply with medication prescriptions.
7. If you drink, limit alcohol.
FRUITS, VEGGIES AND FLAVONOIDS: It’s not surprising that both the DASH plan and the American Heart Association emphasize fruits and vegetables as key to controlling hypertension. These foods are packed with healthy vitamins, minerals and fiber, and when fruits and vegetables occupy more of your plate, you’ll eat less of foods that add to hypertension risk.
Fruits and vegetables are also rich sources of lesser-known phytonutrients called flavonoids. A new French study, published in the American Journal of Clinical Nutrition, reported that women consuming the most flavonoids were less likely to develop hypertension.
The study looked at data on 40,574 healthy French women. Over a 15-year followup period, 9,350 developed hypertension. Women in the one-fifth of the study population who consumed the most of three types of flavonoids were less likely to develop high blood pressure than those in the lowest consumption group: flavonols (10% lower risk), anthocyanins and proanthocyanidin polymers (both 9% lower risk). A similar association was seen for total flavonoid intake.
Flavonoids might help to protect against high blood pressure, although this study was not designed to prove cause and effect. It could be simply that flavonoid intake is a marker for consumption of fruits and vegetables. Either way, the findings support recommendations to put plenty of produce on your plate.
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BERRIES VS. BP: Other recent studies have spotlighted specific plant foods that seem to reduce your risk of hypertension or to lower high blood pressure. It’s important to remember, however, that these apparent benefits are likely not unique to these foods. When blueberries, for example, are found to have blood-pressure effects, it’s quite possible that similar effects might be associated with other berries.
That research on blueberries, published in the Journal of the Academy of Nutrition and Dietetics, compared freeze-dried blueberry powder- equivalent to eating a cup of berries a day – with a placebo powder. The eight-week clinical trial involved 48 postmenopausal women in the early stages of hypertension. Those randomly assigned to the blueberry powder showed improved blood pressure and reduced arterial stiffness; average systolic blood pressure declined 5.1%, while diastolic pressure dropped 6.3%.
“These findings suggest that blueberries may prevent the progression to full-blown hypertension,” the researchers commented. “The changes in blood pressure noted in this study are of clinical significance, as they demonstrate that blood pressure can be favorably altered by the addition of a single dietary component (e.g., blueberries).” (See the April 2015 newsletter for more on blueberries.)
TEA TIME: Although consumed as a beverage, tea can also be thought of as a plant food in terms of its phytonutrients, and several studies have linked drinking tea to blood-pressure improvements. One Australian study, for example, reported that drinking three cups daily of regular black tea was associated with a small but significant drop in blood pressure. At the study’s start, the 95 participants had systolic blood pressure readings ranging from 115 to 150 (normal to stage-one hypertension). After six months, those randomly assigned to drink more tea saw an average drop in systolic pressure of two to three points and about a two-point drop in diastolic pressure, compared to the control group.
Tufts research has also shown that herbal teas containing hibiscus, rich in phytonutrients including anthocyanins, flavones, flavonols and phenolic acids, can help lower high blood pressure. In one study, Diane L. McKay, PhD, a scientist in Tufts’ HNRCA Antioxidants Research Laboratory, recruited 65 pre- or mildly hypertensive volunteers, ages 30 to 70. Those randomly assigned to drink three cups of hibiscus tea per day for six weeks saw a 7.2-point drop in their systolic blood pressure. Those results are comparable to that delivered by standard blood-pressure medications.
Participants with the highest blood pressure at the study’s start showed the most significant reductions – a drop of 13.2 points. That subgroup’s diastolic pressure went down by 6.4 points.
It’s your overall dietary pattern that matters most, of course, as the latest DASH findings demonstrate. But the good news is that you can make a difference in your blood pressure with smart lifestyle choices.
TO LEARN MORE: Hypertension, April 2016—