If your doctor has warned you that your blood pressure is inching up into the unhealthy range, you are not alone. About 1 in 3 American adults have this condition, called prehypertension. And 1 in 3 has hypertension, or high blood pressure.

Ideally, your blood pressure should be below 120/80 millimeters of mercury (mmHg) to reduce your risk of heart disease, stroke, kidney failure and other health problems. When your pressure is in the range of 120/80 mmHg to below 140/90 mmHg, that's pre-hypertension. While it generally won’t qualify you for blood pressure medicine, a level in this range is cause for concern, experts say.

Changing your diet is one smart step you can take. If you have prehypertension, it may help you normalize your pressure and keep you off medications, or at least delay your need for them. It may even help lower your pressure if you have been diagnosed with high blood pressure.

For years, experts have recommended following the DASH (Dietary Approaches to Stop Hypertension) diet. Based on studies sponsored by the National Heart, Lung, and Blood Institute, it focuses on fruits, vegetables, low-fat or fat-free dairy, whole grains, fish, poultry, beans, seeds, nuts and vegetables oils. It's been found to lower blood pressure in some people. More recently, however, researchers have zeroed in on specific foods (many of them a cornerstone of the DASH diet), that seem to provide significant benefit.

We've all heard about how a little dark chocolate may be good for your blood pressure. But have you considered these foods?

Blueberries 

In a small study of 48 women, all past menopause, researchers found that a daily blueberry habit reduced blood pressure, says blueberriesSarah A. Johnson, PhD, RD, the assistant director of the Center for Advancing Exercise and Nutrition Research on Aging at Florida State University in Tallahassee.

"After 8 weeks, postmenopausal women who had early stages of high blood pressure were found to have improved blood pressure and a reduction of stiffness in their arteries, thereby having a beneficial cardiovascular effect," she says. In the study, half of the women took 22 grams of freeze-dried blueberry powder, about the equivalent of a cup of blueberries. (The researchers used powder so everyone would take in the same formula.) The  other half took a freeze-dried placebo that looked identical.                                                        
Those who took the blueberry powder had about a 5 percent drop in their systolic pressure (top number) and 6 percent in the diastolic (bottom). They also produced more nitric oxide, a chemical known to relax blood vessels and thus help pressure, Johnson says. In some, the blood pressure drop wasn't enough to get them to healthy levels, she says, but in others, it was.

The finding ''has to be confirmed by future research," she says, "but we believe by having this effect, eating blueberries may help prevent the progression of hypertension." The study was funded by the U.S. Department of Agriculture and the U.S. Highbush Blueberry Council, an industry group, but Johnson says the industry group had no role in the study itself. 

Beetroot juice

beetroot juice

Drinking a cup of beetroot juice every day may help normalize blood pressure, even if yours is already too high, according to British research. A recent study was small, including 15 men and women who had systolic blood pressures (the top number) of 140 to 159 mmHG but were not yet taking blood pressure medicines. However, those who drank the beetroot juice had a drop in systolic pressure of about 10 mmHg within three to six hours of drinking it, the researchers reported in 2013 in the journal Hypertension. The nitrate in the juice, which converts to nitric oxide in the blood, probably is what helped widen blood vessels and normalize pressure, the researchers speculated. Other experts say beetroot juice works by making arteries less stiff — another route to lowering pressure.                                                                        

A second British study, this one involving 64 participants, found that drinking a glass of beet root juice a day brought down blood pressure by  8/4 mmHg.                                                                                                                                       

Yogurt

yogurt

Eating a six-ounce serving of yogurt a couple of times a week may also keep your blood pressure healthy, according to a study thattracked about 2,100 men and women over 15 years. At the study start, all had normal pressures. Those who had the yogurt habit were 31 percent less likely to develop high blood pressure over the study period than those who did not eat it. Dannon, the yogurt maker, helped fund the study. Participants were part of the well-respected Framingham Heart Study.

The yogurt's calcium may be doing the trick, experts say. Nutrition experts recommend eating non-fat or low-fat yogurt.

Watermelonwatermelon 

A substance in watermelon, L-citrulline, may also be kind to blood vessels. In a very small study of 9 men and women with pre-hypertension, published in 2010 in the American Journal of Hypertension, those who took 6 grams of a watermelon extract for six weeks had lower blood pressure. A second, 2014 study found that substances derived from watermelon extract lowered blood pressure significantly in overweight people with high blood pressure.  

No Single Food is Magic

The blood pressure-lowering effects of any single food can't do it all, of course. Improving your overall diet is key. So is adopting other heart-healthy habits, such as getting regular physical activity and reducing stress.

For some, all the lifestyle changes in the world are simply not enough to bring blood pressure into a safe range. If you've done all you can on the lifestyle front and your pressure readings are consistently high, going on the medication your doctor recommends can reduce your risk of heart disease and stroke. But don’t ditch the lifestyle efforts — sticking with them may mean you’ll need less medication. 

Photo credits in order Brian A Jackson/Shutterstock,  Dani Vincek/Shutterstockmama_mia/ShutterstockSea Wave/Shutterstock

Kathleen Doheny is a Los Angeles journalist specializing in health, behavior and fitness topics.