Nutritional Factors and Blood Pressure
Pao-Hwa Lin.
Duke University Medical Center, Durham, North Carolina, USA
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.