Snacking on raisins may offer a heart-healthy way to lower blood pressure

Even though raisins are popularly cited to lower blood pressure on various websites and are known to have intrinsic properties that could benefit heart and vascular health, researchers believe this is the first controlled study to scientifically support raisins' blood pressure-lowering effects compared to alternative snacks.

"It is often stated as a known fact that raisins lower blood pressure. But we could not find much objective evidence in the medical literature to support such a claim," said Harold Bays, MD, medical director and president of Louisville Metabolic and Atherosclerosis Research Center (L-MARC) and the study's lead investigator. "However, our study suggests if you have a choice between eating raisins or other snacks like crackers and chocolate chip cookies, you may be better off snacking on raisins at least with respect to blood pressure."

In this investigation, Dr. Bays and his team conducted a randomized controlled clinical trial to compare the blood pressure effect of eating raisins versus other snacks in 46 men and women with prehypertension. Participants were randomly assigned to snack on raisins or prepackaged commercial snacks that did not contain raisins, other fruits or vegetables but had the same number of calories per serving three times a day for 12 weeks. The study controlled for individual differences in nutrition and physical activity.

Data analyses found that compared to other snacks, raisins significantly reduced systolic blood pressure at weeks 4, 8, and 12, ranging from -4.8 to -7.2% or -6.0 to -10.2 mmHg (p values <0.05). Within group analysis demonstrated that raisins significantly reduced mean diastolic blood pressure at all study visits, with changes ranging from -2.4 to -- 5.2 mmHg (p values < 0.05). Pre-packaged snacks (including crackers and cookies) did not significantly reduce systolic or diastolic blood pressure at any study visit.

"Overall, these findings support what many people intrinsically believe: that natural foods often have greater health benefits than processed foods," Dr. Bays said.

The study did not identify how raisins lower blood pressure. However, raisins are high in potassium, and have fiber, polyphenols, phenolic acid, tannins and antioxidants.

"Raisins are packed with potassium, which is known to lower blood pressure," Dr. Bays said. "They are also a good source of antioxidant dietary fiber that may favorably alter the biochemistry of blood vessels, causing them to be less stiff, which in turn, may reduce blood pressure."

Although this study was not designed or powered to evaluate for outcomes benefits, other studies support that in patients with prehypertension, mild lowering of blood pressure with medications may have clinical benefits in reducing cardiovascular events.

According to the Centers for Disease Control and Prevention, nearly one in three (28 percent) American adults have prehypertension -- defined as a systolic pressure from 120 to 139 millimeters of mercury (mm Hg) or a diastolic pressure from 80 to 89 mm Hg. This study's findings help validate some current nutritional recommendations. For example, 60 raisins -- about a handful -- contain 1 gram of fiber and 212 milligrams of potassium, which are both recommended in the Dietary Approaches to Stop Hypertension (DASH) diet.

Dr. Bays cautions that this was a single site study; larger trials are needed to confirm the blood pressure-regulating effect of raisins. Nonetheless, he says work in this area is particularly exciting because applying similar scientific methods to natural products, as required for drug development, provides consumers with objective data about which foods may or may not benefit heart health.

This study was funded by the California Raisin Marketing Board through a grant to L-MARC Research Center.