DASH stands for Dietary Approaches to Stop Hypertension
Posted by Rcjohnsen
In Reply to: The DASH diet - http://dash.bwh.harvard.edu posted by Nancy Kenfield
HYPERTENSION:
A DASH of Data in the Salt Debate
Gary Taubes
The controversy over salt, blood pressure, and public health has seemed endless
and intractable. The National Heart, Lung, and Blood Institute (NHLBI) and the
National High Blood Pressure Education Program, among other august bodies,
recommend that all individuals, not just those with hypertension, reduce the
amount of salt in their diets to lower their blood pressure and improve their
health, while a good proportion of the researchers in the field believes such
recommendations have not been supported by the data. As a result, an entire
field has been mired in acrimony for 4 decades.
On 17 May, Claude Lenfant, director of NHLBI, declared the controversy over.
The results of DASH-Sodium, a new NHLBI-funded study to be presented the next
day at the annual meeting of the American Society of Hypertension (ASH), had
made the health benefits of salt reduction unambiguous, Lenfant said. After the
meeting, the controversy showed little sign of abating, however.
DASH stands for Dietary Approaches to Stop Hypertension. DASH-Sodium is the
sequel to the original DASH study published in April 1997, which suggested that
blood pressure could be reduced dramatically by eating a diet rich in fruits,
vegetables, and low-fat dairy products. Salt was not a factor in the original
DASH study, which made the blood pressure reductions that much more noteworthy.
In DASH-Sodium, a collaboration of five institutions, investigators tested both
the DASH diet and a control diet, similar to that of the average American, at
three levels of salt intake--8 grams a day, which is slightly less than the
average American's intake; 6 grams, equivalent to the current government
recommendations; and 4 grams. The investigators randomly assigned 412 subjects
with either hypertension or high normal blood pressure to either the control
diet or the DASH diet for 90 days. They fed them all their meals--assuring that
subjects were eating their assigned diets, no more, no less--and changed the
sodium level every 30 days.
The results were impressive. The DASH diet alone reduced blood pressure as
dramatically as before. And the reductions in blood pressure by decreasing
salt, whether on the DASH diet or the control diet, while not quite as
impressive, were still substantial. When hypertensives, for instance, went from
the high-salt to the low-salt control diet, their systolic blood pressure fell
8.3 millimeters of mercury (mmHg) and diastolic fell 4.4 mmHg (8.3/4.4 mmHg).
This drop is comparable to that achieved by blood pressure- reducing drugs. In
those with high normal blood pressure, going from high sodium to low sodium on
the control diet reduced blood pressure by 5.6/2.8 mmHg, a drop almost five
times greater than recent meta-analyses might have predicted. The better part
of these blood pressure reductions came when the subjects went from the
government-recommended levels of 6 grams of salt a day to the lowest level of 4
grams. "The finding suggests that an intake below that now recommended could
help many Americans prevent the blood pressure rises that now occur with
advancing age," said Lenfant in a press release.
Protracted controversies, however, can be remarkably resistant to new data,
even good data. After hearing the DASH-Sodium results at the ASH meeting, those
who were skeptical of the wisdom of recommending that an entire nation eat less
salt remained resolutely skeptical. David McCarron, for instance, of the Oregon
Health Sciences University in Portland, pointed out that for those with normal
blood pressure eating the healthy DASH diet, reducing salt from 8 grams to 4
grams a day made little difference in blood pressure (1.7/1.1 mmHg). "If you
are eating the healthy DASH diet and you have normal blood pressure, sodium
restriction has almost no effect. ... So why should salt reduction be the major
message, when it says if you go on a healthy diet, salt reduction is a moot
point?"
A stickier issue speaks to the nature of public health recommendations. The
better part of the salt controversy centered not on the size of the blood
pressure reductions that could be achieved by eating less salt, but on whether
it would improve our health to do so. Over the years, researchers have been
unable to demonstrate that reducing salt improves health. The authors of a 1998
comprehensive meta-analysis on salt reduction published in The Journal of the
American Medical Association concluded that "The optimum solution to the
controversy are long-term trials with hard end points, such as stroke, acute
myocardial infarction, and survival."
This conclusion was echoed after the ASH meeting by Micky Alderman, a
hypertension specialist at Albert Einstein College of Medicine in New York City
and a past president of ASH. "They're suggesting as a remedy for 250 million
people that they cut sodium intake in a half," says Alderman, "and to do so
solely on the basis of showing you can change blood pressure for a 30-day
period, without even assessing any other potentially adverse consequences. It
seems to me it's a leap of faith."
Although DASH-sodium investigators were much more sanguine about the health
benefits of salt reduction, at least one agreed that Alderman's point was
reasonable. Biostatistician William Vollmer of the Kaiser Permanente Center for
Health Research in Portland told Science that he believes DASH-Sodium provides
good evidence for recommending lower levels of salt intake. Nonetheless, he
added, "it would be nice to see a good, controlled study that shows the
long-term effects of a low-sodium diet. The issue has been raised. We can sit
here and say it hasn't, or we can do a study that settles it once and for all."
Follow Ups:
Post a Followup
