DASH diet plus dietary sodium lowers blood pressure

The DASH diet, a diet rich in fruit, vegetables and low-fat dairy foods, combined with reduced dietary sodium, lowers blood pressure for all persons, according to new research released this week.

The Dietary Approaches to Stop Hypertension study was supported by the National Heart, Lung, and Blood Institute (NHLBI). A detailed analysis showed the blood pressure lowering effects of the DASH diet and reduced dietary sodium in a wide variety of population subgroups: persons with and without hypertension or a family history of hypertension, older and younger adults, men and women, African-American and other races, obese and non-obese, as well as people with higher or lower physical activity levels, larger or smaller waist circumferences, and higher or lower annual family income or education.

While the combination of the DASH diet and reduced dietary sodium produced the biggest reductions, each intervention also lowered blood pressure for all groups when used alone.

The DASH diet is rich in fruits, vegetables, and low-fat dairy foods with a reduction in total and saturated fat. The diet is also rich in potassium, calcium, magnesium, fibre, and protein. Prior studies have found that the DASH diet lowers blood pressure and also lowers blood LDL-cholesterol (the "bad" cholesterol) and the amino acid homocysteine, which appears to increase the risk of heart disease. Prior studies also showed that a reduction in dietary sodium lowers blood pressure, both with and without the DASH diet.

"This new study underscores the blood pressure-lowering effects of a reduced intake of salt and other forms of dietary sodium,"​ said NHLBI Director Dr. Claude Lenfant. "Earlier research on the link between sodium and blood pressure had given conflicting results in various population groups. Now, we can say that cutting back on dietary sodium will benefit Americans generally and not just those with high blood pressure."​

"The study's participants have blood pressures in the same range as half of adult Americans, including about 80 per cent of those age 50 and older,"​ said Dr. Frank Sacks, Professor of Cardiovascular Disease Prevention, Harvard School of Public Health and chair of the DASH Steering Committee. "Adopting these measures could help millions of Americans avoid the rise in blood pressure that occurs with advancing age."​

High blood pressure, also called hypertension, is a major risk for heart disease and the chief risk factor for stroke.

The new data comes from the DASH-Sodium study, a multicentre, 14-week randomised "feeding" trial in which all food was provided to 412 participants, aged 22 and older, and with systolic blood pressures of 120-160 mm Hg and diastolic blood pressures of 80-95 mm Hg.

Fifty-two per cent of the participants were women and 48 per cent men; 54 percent were African American, 42 per cent white, and 10 per cent other races. Forty-one per cent had hypertension and 59 per cent did not.

For 3 months, participants ate either the DASH diet or a typical American diet. Weight was kept stable. During the study period, each group followed three different intakes of dietary sodium for 1 month each in random order. The sodium levels were 3,300 milligrams a day (the average level consumed by Americans), 2,400 milligrams a day (the upper limit currently recommended by the National High Blood Pressure Education Program), and 1,500 milligrams a day.

The largest blood pressure differences occurred for those on the DASH diet with a daily sodium intake of 1,500-milligrams compared with those on the control diet with a sodium intake of 3,300 milligrams.

Detailed analysis showed that the DASH diet and reduced sodium intake reduced blood pressure for all the population subgroups studied.

"Following the DASH diet and reducing the intake of dietary sodium are two non-drug approaches that work to control blood pressure,"​ said Dr. Denise Simons-Morton, Leader of the NHLBI Prevention Scientific Research Group and a DASH co-author. "The blood pressure reductions achieved from this combination came in only 4 weeks and persisted through the duration of the study. Ideally, Americans should use both the DASH diet and reduced sodium approaches but, even if they do only one, they'll still reap significant health benefits.​

"If the U.S. food supply were lower in sodium," added Simons-Morton, "it would help lower levels of blood pressure in the general population."​

More information about the DASH diet and related heart-health topics can be found online at http://www.nhlbi.nih.gov.