Lower the dietary sodium, lower the BP: the DASH-Sodium study

Susan Jeffrey

January 04, 2001

Thu, 04 Jan 2001 21:02:43

Boston, MA - Results of the DASH-Sodium study - using a dietary approach proven to lower blood pressure (BP)- with the added twist of very low sodium intake (1.5 g per day) - show that the lower the dietary sodium levels achieved, the lower the BP over follow-up, even among normotensive subjects. These findings should bolster proposed changes in dietary guidelines targeting reductions in sodium, according to an editorial accompanying the publication appearing in the January 4, 2001 issue of the New England Journal of Medicine.

"The reduction in sodium intake to levels below the current recommendation of 100 mmol per day and the DASH diet both lower blood pressure substantially, with greater effects in combination than singly," the researchers, led by Dr Frank M Sacks (Brigham and Women's Hospital, Harvard Medical School) concluded. "Long-term health benefits will depend on the ability of people to make long-lasting dietary changes and the increased availability of lower sodium foods."

The DASH diet

In 1997, these researchers published results of a randomized trial focused on a new dietary approach to treating hypertension, a diet that has come to be known as the Dietary Approaches to Stop Hypertension (DASH). The diet emphasizes fruits, vegetables, and low-fat dairy foods, and includes whole grains, poultry, fish, and nuts. It is reduced in, but does not exclude, red meat, sweets, and sugar-containing beverages. The result is a diet high in potassium, calcium, and magnesium, as well as protein and fiber. The implementation of the diet was described in some detail in the August 1999 issue of the Journal of the American Dietetic Association.

In the field of BP research, the role of sodium in determining BP and the efficacy of sodium restriction in reducing BP have been hotly debated topics. In the first DASH trial, sodium levels were kept constant. In the DASH-Sodium trial, the researchers compared the effect of lowering sodium consumption, both in combination with the DASH diet, or combined with a control diet meant to simulate that consumed by most of the US population. In both groups, all participants consumed 3 different levels of sodium over consecutive 30-day periods. All food was provided.

The "higher" intake of sodium was 143 mmol per day, or 3.3 g. Intermediate sodium intake was about 106 mmol per day, or 2.4 g, the upper limit of current guidelines for hypertension prevention and treatment. "Low" sodium intake was 65 mmol per day, or 1.5 g, which the researchers hypothesized would be an optimal level. A total of 412 participants were enrolled; about 57% were women, and 57% were African-American. Systolic BP at baseline ranged from 120 to 159 mm Hg, and diastolic BP between 80 and 95 mm Hg. About 41% were hypertensive.

"A food industry issue"

The researchers found that reducing sodium intake from the high to the intermediate level reduced systolic BP by 2.1 mm Hg (p<0.001) among subjects on the control diet, and by 1.3 mm (p=0.03) among subjects on the DASH diet which itself lowers BP. Reducing sodium intake from the intermediate to the lower level resulted in an additional drop in systolic pressure of 4.6 mm Hg among those on the control diet, and 1.7 mm Hg (p<0.01) in those on the DASH diet.

These effects were seen in subjects with and without hypertension, although the effects were greater in hypertensive subjects. Similarly, the effects were seen in all racial groups, and in both genders, but appeared enhanced among African Americans and women.

When the control diet with the highest sodium was compared to the DASH diet with lowest sodium, the systolic BP was 7.1 mm Hg lower among patients without hypertension, and 11.5 mm Hg lower in those with hypertension.

When Sacks first presented these findings (previously reported by heart wire in May 2000 at the American Society of Hypertension meeting), he pointed out that these effects were similar to those seen with antihypertensive medications. Adherence to the low-sodium diet was good, he said, and people seemed to "lose their taste" for salt over time. "Where we need to go now is to see how to apply that and to help people get their salt down, and that, I think, is a food industry issue," Sacks said at the time.

Findings applicable to most Americans

In an editorial accompanying the publication, Dr Philip Greenland (Northwestern University Medical School, Chicago, IL) wrote that both observational studies and the DASH trials provide support for the idea that a healthful overall dietary pattern, rather than concentration on certain foods or nutrients, has a role in reducing the risk of chronic disease.

"The new findings of the DASH-Sodium trial strengthen the scientific basis for continuing to advise all persons to reduce their dietary salt intake from the current US mean level of nearly 9 g to less than 6 g of salt per day," Greenland writes. "The DASH-Sodium investigators suggest that a further reduction to about 3 g of salt per day may be justified, but that it would be very difficult to achieve without cooperation from the food industry, since much of the salt in the US diet comes from prepared foods, rather than from salt added in cooking or at the table."

 

The main message of this new trial, stated forcefully by the authors, is that the results appear to be applicable to most people in the United States.

 

That kind of change would require governmental action in terms of legislation or labeling requirements, the editorialist said, but at the very least, the DASH-Sodium results provide no basis for "backing away" from the 6-g recommendation.

"The main message of this new trial, stated forcefully by the authors, is that the results appear to be applicable to most people in the United States," Greenland concluded. "The widespread adoption by all persons, with or without hypertension, of sound dietary guidelines, such as those of the American Heart Association, should result in improved control and prevention of hypertension, as well as broad improvement in other measures of health."



Go for a low-fat, not just a low-salt, diet, say industry representatives

New York, NY- Although there's little doubt that lowering salt can lower blood pressure, the way to go about it is another story, say salt industry representatives in media reports on January 4, 2001. The DASH study "lays to rest the long-standing controversy over whether sodium reduction lowers blood pressure," says Dr Claude Lenfant (Director, National Heart, Lung, and Blood Institute) in a CNN report. "The Salt Institute - and researchers who are paid consultants to the group - didn't argue with the study results, but disagreed with the authors' interpretation of the data," reports CNN. Dr David McCarron (Professor of Medicine, Oregon Health Sciences University) told CNN that the study results show that "going on the low-fat diet does a much better job of lowering blood pressure than cutting back on salt," and he encouraged people to make overall dietary changes: "When you tell people to cut something out, they say 'I don't want to hear that.' People are more willing to listen to positive messages." CNN notes that McCarron is on the Salt Industry's scientific advisory board and has been paid as a consultant.

Peter Cleary (Grocery Manufacturers of America), a spokesman for a trade group that represents Campbell Soup Co, Lay's owner PepsiCo and other salty-food producers such as Diamond Crystal Brands Inc agrees, telling the Wall Street Journal: "Why focus on the negative message?" Lead author Dr Frank Sacks told CNN that both salt reduction and a low-fat diet are "important," adding, "it's shameful that anyone in the field would say [a 4-point decrease] is unimportant. That's more than half the effect of a drug." Richard Hanneman (President, The Salt Institute) told CNN he thinks it's useless telling Americans to cut back on salt: "We don't think it's possible for the government to legislate or regulate a reduction in sodium content. It would be like legislating morality."

In an interview with Reuters Health, study co-author Dr Eva Obarzanek said that because of the American lifestyle and food choices, lowering salt intake to about 1500 mg daily would not be easy, particularly with all the hidden salt in processed foods. "It is necessary to get help from the food industry and restaurants and fast food places,'' Obarzanek says. "Lower salt and the DASH diet should be recommended to the general population in hopes of preventing hypertension and the rise of blood pressure that occurs with advancing age."

-Mark L Fuerst




Related links

1.

2. [Heartwire > News; Aug 22, 2000]

3. [Heartwire > News; May 19, 2000]

4. [Heartwire > News; May 18, 2000]


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