A DASH OF SALT AND TONE: RECENT TRIALS PROVIDING NEW INSIGHTS
INTO THE DIET-BLOOD PRESSURE-HEALTH LINK
Myron H. Weinberger, M.D.
Hypertension Research Center
Indiana University School of Medicine
Several recent trials have provided new information regarding the relationship between
dietary constituents and the sensitivity of blood pressure to salt to blood pressure
levels over a short term of intervention, and to mortality over the long-term. Since
lifestyle modifications and dietary changes are currently recommended as the first
step in the prevention or treatment of high blood pressure and since such approaches
are efficacious in lowering blood pressure, relatively economical and risk-free
for most individuals, they have great appeal. This article will address the substance
of some of these recent findings.
Salt sensitivity of blood pressure can be demonstrated in the majority of hypertensive
patients and in as many as 25% of the normotensive population (1). Moreover, in
normotensive subjects who are salt-sensitive there is a greater blood pressure increase
with time (age) than among those who are not salt-sensitive (2). Thus the age-related
increase in blood pressure, even among normotensives, is related to salt intake.
Salt-sensitivity of blood pressure is more frequently observed in older subjects
(2) and among those of African-American descent (1). A recent follow-up study of
individuals who were initially classified with respect to salt responsiveness of
blood pressure as long as 25 years ago or more, has revealed that normotensive salt-sensitive
individuals have the same decreased survival as those who are hypertensive, whether
salt-sensitive or salt-resistant and all 3 groups have reduced survival compared
to those who are salt-resistant and normotensive (3). It is speculated that the
reduced survival of these salt-sensitive normotensive subjects may be related to
an increased risk for the subsequent development of hypertension. It should be emphasized
that salt sensitivity is a continuous variable and thus the separation of individuals
into salt sensitive and salt resistant groups is based on arbitrary criteria. The
differences between the groups, therefore, are of degree rather than being qualitative
ones. But what of those who are already hypertensive or who have blood pressure
in the "high-normal" (130-139/85-89) range?
The TONE (Trial of Nonpharmacologic Interventions in the Elderly) Trial included
681 hypertensive subjects aged 60-80 who participated in a 2 x 2 factorial trial
of weight loss + reduced salt intake, reduced salt intake alone, weight loss alone,
or neither (4). When those assigned to reduced salt intake alone were compared to
those maintaining their usual lifestyle (neither) an average reduction in dietary
sodium intake of 40 mmol/d was observed based on 24-hour urine collections. This
modest change in salt intake was associated with a significant (p<0.001) decrease
in both systolic and diastolic blood pressure for the 30-month duration of the study.
The lowering of blood pressure permitted reduction or elimination of antihypertensive
medications (p<0.001) as well as demonstrating a trend to reduced cardiovascular
events over the short study period in the group assigned to dietary salt reduction
compared to the Usual Lifestyle group. More importantly, no adverse effects were
observed related to the modest degree of dietary salt reduction in these older subjects.
These observations speak directly to the benefit and safety of reducing dietary
salt intake in elderly hypertensives and the possibility that this approach may
be useful or preferable among those in whom medical therapy is not feasible or desirable.
The DASH (Dietary Approaches to Stop Hypertension) trial (5) was conducted in individuals
with "high-normal" and Stage 1 hypertension randomly assigned to receive
a "normal" diet, a diet enriched in fresh fruits and vegetables and a
diet enriched in fresh fruits and vegetables and low-fat dietary products. Estimates
of sodium intake indicated a modest reduction to an average of about 130 mmol/d.
The group receiving the diet enriched with fresh fruits and vegetables and low-fat
dairy products had the lowest blood pressure levels during the study followed by
the group assigned to fresh fruits and vegetables which was lower than the blood
pressure observed with the control diet. These findings supported the concept that
dietary enhancement of potassium, magnesium and calcium intake contributed to blood
pressure reduction. However, because of the modest reduction of dietary salt intake
among all three groups, the possibility of an interaction of the study diets with
a reduced salt intake could not be excluded. This set the stage for yet another
study to examine this issue.
The DASH-II Trial assigned individuals with blood pressure ranging from 120/80 to159/95
to a control diet or the DASH combination diet randomized to one of three dietary
sodium levels, high (150 mmol/d), intermediate (100 mmol/d) or low (50 mmol/d) in
a randomized, crossover design (6). Adherence to the goal sodium intake was quite
good as evidenced by urinary sodium excretion of 143 mmol/d on the high, 107 mmol/d
on the intermediate and 66 mmol/d on the low sodium diets, respectively. There was
a stepwise reduction in blood pressure with each level of reduced salt intake on
both the control and DASH combination diets. The difference in blood pressure between
those on the highest and lowest levels of sodium intake receiving the DASH diet
averaged 12 mm Hg, a response equal to that of potent antihypertensive drugs. The
DASH diet had a greater effect to reduce blood pressure on the two higher levels
of salt intake in comparison to the control diet. Individuals of African-American
background had the greatest decrease in blood pressure with dietary salt reduction
when compared to the other subgroups examined. As in the earlier DASH trial, no
adverse effects of dietary salt reduction were observed.
What then are the implications of these studies? They demonstrate that dietary interventions
consisting of reduced salt intake and increased use of fresh fruits, vegetables
and low-fat dairy products can effectively reduce blood pressure in substantial
proportions of the population with no adverse effects noted at the levels evaluated.
Further, individuals typically considered to be at the highest risk for hypertension
and cardiovascular events, the elderly and African-Americans, had the greatest reduction
in blood pressure with these dietary alterations. These findings have great implications
for the prevention of hypertension as well as for non-pharmacologic treatment for
those with established hypertension and the possibility of reducing the need for
expensive and problematic antihypertensive drug therapy. Moreover, the adoption
of diets modestly reduced in salt content holds out the potential of preventing
the future development of hypertension in susceptible individuals and populations
with virtually no risk.
1) Weinberger MH, Miller JZ, Luft FC et al. Hypertension 1986:8(Pt 2):127-134.
2) Weinberger MH, Fineberg NS.Hypertension 1991;18:67-71.
3) Weinberger, MH, Fineberg NS, Fineberg SE, Weinberger M. Hypertension 2001;37(Pt2):429-432.
4) Appel LJ, Espeland MA, Easter L et al. Arch Intern Med 2001;161:685-693.
5) Appel LJ, Moore TJ, Obarzanek E, et al. New Engl J Med 1997;336:1117-1124.
6) Sacks FM, Svetkey LP, Vollmer WM, et al. New Engl J Med 2001;344:3-