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DASH diet and less salt lowers blood pressure

This second DASH study is very important, and it will, I believe, temper what has been a very heated debate among physicians over whether reducing salt in one’s diet reduces blood pressure. It presents very clear, statistically significant evidence that for people with and without high blood pressure, for men and women and people of different racial backgrounds, reducing dietary salt helps lower blood pressure.

The original DASH study was undertaken to test the observation that vegetarians tend to have lower blood pressure than nonvegetarians. Since vegetarians consume higher levels of fiber, more fruits and vegetables and more minerals, such as magnesium and potassium, researchers compared subjects who consumed a diet comparable to that of vegetarians with those who ate a more typical American diet, higher in saturated fat, lower in fiber and fruits and vegetables.

The most dramatic results were noted in hypertensive patients whose systolic and diastolic blood pressure dropped by 11.4 mm Hg and 5.5 mm Hg, respectively. These are very significant drops, comparable to results obtained by placing patients on medication to lower blood pressure.

Nonhypertensives benefited as well with drops of systolic and diastolic blood pressure of 3.5 mm Hg and 2.1 mm Hg, respectively. It’s important to note these beneficial results were seen even when weight and alcohol and salt consumption remained the same.

New DASH study strengthens the case
The DASH data has now been extended to factor in the role of salt. Subjects in this study, which included both hypertensive patients and those with normal blood pressure levels, were randomly assigned to follow the DASH diet or a more typical American diet. These two groups were further divided into three categories:

• those who ate 3.3 grams of salt a day, the amount in the average American diet;
• those who ate 2.4 grams per day, the current recommended level; and
• those who ate 1.5 grams per day.

At each of the three levels of sodium intake, blood pressure was lower for those on the DASH diet than for those on the control diet.

The highest benefit was observed among hypertensives and the elderly who were assigned to the lowest salt category and who were in the DASH diet group. Their systolic and diastolic blood pressure dropped by 11.5 mm Hg and 7.1 mm Hg, respectively. Participants who ate the more typical American diet but who were in the lowest salt category also benefited. More than half of their blood pressure reduction occurred when they reduced their salt intake from the intermediate to the lower level. The results show us reducing salt intake lowers blood pressure in addition to the benefits obtained by consuming the DASH diet alone.

There are individual variations in response to reduced salt intake. Recent research indicates individuals with the "AA" variation of the angiotensinogen gene are more sensitive to salt and are more responsive to nutritional strategies to reduce blood pressure than those who do not carry this variation of the gene, but everyone does benefit.

The DASH-Sodium researchers estimate that if Americans were to reduce salt consumption to 1.5 grams a day, the prevalence of heart disease and stroke would decrease by 20 and 35 percent, respectively.

Additional evidence
If that’s not enough evidence, researchers added to the growing body of data linking nutritional approaches to the prevention of hypertension and heart disease at a conference held earlier this year by the American Heart Association.

• Blood clotting and inflammation in obese patients who ate whole grains was reduced by 30 percent.
• After 19 years, patients in the very large NHANES-1 database who consumed fruits and vegetables three to four times a day lowered their risk of stroke by 48 percent.
• The addition of 40 grams of soy protein to the daily diet reduced systolic blood pressure by 3.01 mm Hg more than in patients on a placebo diet.
• Reductions in blood pressure were also reported with daily increases of omega-3 and linolenic acids, found in such foods as mackerel, olive oil, tofu and flax seed. For each two grams of additional omega-3 or linolenic acid consumption, both systolic and diastolic blood pressures were lowered by 1 mm Hg.

What do we recommend?
Based on this dramatic evidence, what do we suggest? Avoid processed foods and foods very high in salt such as pickles, potato chips and canned soups. If you are like many Americans who crave salty foods, you may discover as did subjects in the DASH-Sodium study, that you begin to lose your taste for salt just two days after beginning a low-salt regimen.

Interestingly, the DASH diet is very similar to the Mediterranean diet we discussed in a HealthLINK feature last year, which also has been shown to reduce the risk of heart disease. There is ample evidence that a diet rich in fruits and vegetables, high in grains but low in total and saturated fats and salt, supplemented by omega-3 and linolenic acids, could significantly reduce the high rates of heart disease and stroke in the U.S.

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Dr. Mukherjee is a partner with Cardiology Associates of New Haven, 40 Temple Street, New Haven, CT. He is an attending physician at Yale-New Haven Hospital and an assistant clinical professor of medicine and cardiology at the Yale School of Medicine.