Nutritional Factors and Blood Pressure
Duke University Medical Center, Durham, North Carolina,
Diet is well recognized to be closely related to the control
of blood pressure. Numerous observational studies have shown that people
in non-industrialized nations generally have lower blood pressures and
blood pressure increases less with age than do people of industrialized
countries. The vegetarian population often has lower blood pressures as
well, even within the same society as compared to like nonvegetarians.
However, when dietary hypotheses generated from these observational studies
are tested in clinical trials, results have been inconsistent. For the
most part, these trials have examined only a single nutrient at one time.
Minerals such as calcium, magnesium and potassium, often studied as supplement
pills, are usually shown to have either small or no effect on blood pressure.
Trials testing the effects of the amount and type of fat and protein have
generally shown no effect on blood pressure. On the contrary, when multiple
nutrients, studied within a whole dietary pattern such as trials of vegetarian
diets and the recent Dietary Approaches to Stop Hypertension (DASH) Study,
positive findings on blood pressure were found. The DASH study was designed
to study the effects of three dietary patterns on blood pressure a typical
American diet, a diet rich in fruits and vegetables and a combination diet
that emphasizes fruits, vegetables and lowfat dairy products. A total of
459 adults with blood pressure of less than 160 mm/Hg systolic and between
80 and 95 mm/Hg diastolic completed the study. The three dietary patterns
were planned to differ in multiple nutrients including total fat, saturated
fat, cholesterol, protein, fiber, calcium, magnesium and potassium. Body
weight and sodium content of each dietary pattern were held constant. This
controlled feeding study showed that the combination diet, which contained
higher amounts of calcium, magnesium, potassium, and fiber, and less total
and saturated fats and cholesterol, reduced blood pressures significantly
(5.5 mm/Hg SBP and 3.0 mm/Hg DBP) relative to change in the control group.
The reduction was even greater among the hypertensives (11.4 mm/Hg SBP
and 5.5 mm/Hg DBP). It is possible that effects of individual nutrients
are small and difficult to detect in trials modifying only a single nutrient.
Therefore, results observed in the DASH study may be additive effects of
multiple nutrients. In addition, DASH study modified whole dietary patterns
containing nutrients naturally occurring in foods which may be more effective
in reducing blood pressure than nutrients provided in supplemental pills.