By: Thomas Pickering, MD, DPhil, FRCP, Director of Integrative and Behavioral Cardiology Program
of the Cardiovascular Institute at Mount Sinai School of Medicine, New York.

One of the major breakthroughs in the treatment of hypertension in the past few years has been the DASH diet (DASH stands for Dietary Approaches to Stop Hypertension). This resembles the Mediterranean diet in that it has little red meat, a lot of fruits and vegetables, and also a lot of grains. Unlike the Mediterranean diet, however, it also has low fat dairy products, The original diet, which was shown to lower blood pressure very effectively, had the same calories and sodium content as the average American diet. The reason why it lowers blood pressure is that it contains a lot of potassium, magnesium, and calcium.

A second DASH study, the results of which were presented at the American Society of Hypertension meeting in New York on May 18 2000, has examined the effects of varying the salt content of the diet. There were 412 patients with blood pressure in the “high normal” or mildly hypertensive range, who were randomly allocated to eat either a regular American diet or the DASH diet for three months. This was done by providing them with specially prepared meals. For each one of the three months the salt content was varied; the “high” salt diet had 143 milliequivalents of sodium (3.3 grams), which is the same amount as the typical American diet; The medium salt diet had 106 milliequivalents (2.1 grams), and the low salt diet had 65 milliequivalents (1.5 grams).

While eating the regular US diet, the effect of salt restriction was to lower systolic pressure by 2.1 mmHg on going from the high to the medium salt intake, and by a further 4.6 mmHg on going from the medium to the low salt intake. Thus the effect of going from a high to a low salt intake was 6.7 mmHg. While on the DASH diet the same changes were seen, although a little smaller (4.0 instead of 6.7 mmHg). For people with mild hypertension, the reduction of blood pressure achieved by the combination of the DASH and low salt diet was 11.5/5.7 mmHg (systolic/diastolic), which is equivalent to the changes seen with blood pressure lowering medications.

These are important findings, and confirm the effects of salt intake on blood pressure, as well as showing an additive effect between salt intake and the DASH diet. One reason why the effects were so strong is that the participants were provided with prepared foods, so that achieving the desired dietary intakes was less of a problem than in other studies where the participants themselves have to prepare or choose what they eat.