Funded by the National Heart, Lung and Blood Institute, Dietary Approaches to Stop Hypertension (DASH) was a major research study to determine whether diet can lower blood pressure. High blood pressure (hypertension) is a major risk factor for coronary artery disease (which can lead to heart attack) and carotid artery disease (which can lead to stroke). The goal of the DASH study was to determine whether a particular diet could lower blood pressure, reducing the risk of potentially fatal events.

The DASH study examined the impact of three different dietary patterns on a group of 459 subjects with blood pressures of less than 160/80-95. The participants included men and women (Caucasian and black American) averaging 45 years old. They were placed in one of three dietary plans: typical American diet, typical diet plus more fruits and vegetables, and the DASH diet.

All three groups consumed the same amount of salt (3,000 mg per day, slightly less than the average intake of Americans at 3,600 to 4,000 mg per day) and calories. Alcohol was limited to one to two drinks a week in all groups.

At the end of the study, there was a significant difference among the groups. The participants who incorporated fruits and vegetables into their diet and those who followed the DASH diet lowered their blood pressure. The DASH followers, however, had the greatest reduction in blood pressure, especially for those with hypertension.

Follow-up research suggested that the DASH diet is even more effective for black Americans than it is for Caucasians. Identifying an effective treatment for black Americans is particularly important because they are at higher risk of developing high blood pressure.

Before the introduction of the DASH diet, the main dietary change recommended for patients with high blood pressure was a reduction of salt. However, the DASH study demonstrated that other dietary changes could also be effective in reducing blood pressure.

To further investigate the effects of salt on blood pressure, a second phase of research was performed. The DASH-Sodium trial investigated the relationship between blood pressure and sodium intake. Participants in this study followed either a typical American diet or the DASH diet. In addition, they were instructed to modify their sodium intake in one of the three ways:

• High sodium diet (3,300 milligrams of sodium per day)
• Intermediate sodium diet (2,300 milligrams of sodium per day)
• Low sodium diet (1,500 milligrams of sodium per day)

The results indicated that reducing sodium intake lowered blood pressure for both the typical diet and the DASH plan. In fact, the more the sodium level was reduced, the greater the blood pressure fell. The biggest reduction in blood pressure was found in the group that followed the DASH diet at the lowest level of sodium intake, or 1,500 milligrams daily.