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Abstract & Commentary
Synopsis: The DASH diet combined with low sodium intake can lower systolic blood pressure more than 10 mm Hg after only 30 days.
Source: Sacks FM, et al. N Engl J Med 2001;344:3-10.
The dietary approaches to stop hypertension (dash) trial demonstrated that a diet that emphasizes fruits, vegetables, and low-fat dairy products, that includes whole grains, poultry, fish and nuts, that contains small amounts of red meat, sweets, and sugar-containing beverages, and that contains decreased amounts of total and saturated fat and cholesterol, lowers blood pressure substantially both in people with hypertension and those without hypertension.1
The effect of large amounts of sodium in the diet has been controversial, however. This study was designed to evaluate the effects of varying amounts of sodium in the diet. A total of 412 participants were randomly assigned to eat either a control diet typical of the intake in the United States or the DASH diet. Within the assigned diet, participants ate foods with high, intermediate, and low levels of sodium for 30 consecutive days each, in random order. The primary outcome was systolic blood pressure at the end of each 30-day period of dietary intervention. The secondary outcome was diastolic blood pressure.
Reducing the sodium intake from high to the intermediate level reduced the systolic blood pressure by 2.1 mm Hg (P < 0.001) in the control diet (the so called average American diet) and 1.3 mm Hg in the DASH diet. Reducing the sodium intake from the intermediate level to the low level caused additional reductions of 4.6 mm Hg in the control diet (P < 0.001) and 1.7 mm Hg in the DASH diet (P < 0.01). The effects of sodium were observed in participants with and in those without hypertension, blacks, and those of other races, and both women and men. The DASH diet was associated with significantly lower systolic blood pressures than the control diet at each sodium level. As compared with the control diet with a high sodium level, the DASH diet with a low sodium level led to a systolic blood pressure that was 7.1 mm lower in participants without hypertension, and 11.5 mm Hg lower in participants with hypertension.
Comment by Ralph R. Hall MD, FACP
The first report of the DASH diet1 made significant additions to the prevention and treatment of hypertension. The findings were rapidly incorporated into the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure2 and have more recently influenced the guidelines released by the American Heart Association.3
The first DASH trial maintained the sodium intake at 3 g per day and still resulted in significant drops in both systolic and diastolic blood pressure. This latest study varied the sodium intake from 3.5 g, 2.3 g, and 1.3 g per day in both the DASH and control diets. There was a reduction of 8.9 mm Hg in systolic blood pressure and 4.5 mm Hg in diastolic blood pressure between the high and low sodium intake. Greenland notes in the accompanying editorial4 that the blood pressure reductions in this study are similar to the ones achieved with blood pressure lowering medications.
These findings have great importance when one considers the findings of Cook that a reduction in diastolic pressure of 2 mm Hg results in a decrease of 6% in coronary heart disease and a 15% decrease in stroke.5
In the past, most nutrition studies have emphasized the specific effects of one nutrient factor. Jacques and Tucker use the example of diets high in fiber which "tend to be high in vitamin C, folate, various carotenoids, magnesium, potassium. So when we see the association between fiber and disease risks, can we be certain the relation is not a consequence of folate or carotenoid intake."6 As they point out, the DASH diet along with other recent successful studies, are examinations of dietary patterns. They provide strong evidence that dietary patterns can be significantly related to measures of health and an important approach to nutrition research.
If we examine these diets we note that many of us have been on the wrong track. We have used low-fat mayonnaise and shunned nuts and, thus, in reducing our total fat intake, have reduced gamma vitamin E, the "good fats," and potentially beneficial flavonoids from our diet.
Now, how do we put these nutrients back into our diet without gaining weight? The widespread use of these diets will call for both physician and patient education!
1. Appel LJ, et al. N Engl J Med 1997;336:1117-1124.
2. Arch Intern Med 1997;157:2413-2446.
3. Krauss RM, et al. Circulation 2000;102:2284-2299.
4. Greenland P. N Engl J Med 2001;344:53-55.
5. Cook NR. Arch Intern Med 1995;155:701-709.
6. Jacques PF, Tucker K. Am J Clin Nutr 2001;73:1-2.