Calcium and high blood pressure

Some observational studies (type of research study in which the treatment/intervention is observed and not controlled by the researchers) and experimental studies (type of research study in which the researchers control the treatments/interventions and that are assigned to participants) indicate that individuals who eat a vegetarian diet high in minerals (including calcium, magnesium and potassium) and fiber, and low in fat, tend to have reduced blood pressure.

Findings from some clinical trials (a specific type of experimental study) used to evaluate the effects of one or more treatments/interventions in humans) indicate that an increased calcium intake lowers blood pressure and the risk of hypertension (high blood pressure). However, the results of some studies produced small and inconsistent reductions in blood pressure. One reason for these results is because these research studies tended to test the effect of single nutrients rather than foods on blood pressure.

To help test the combined effect of nutrients including calcium from food on blood pressure, a study was conducted to investigate the impact of various dietary eating patterns on blood pressure. This study titled "Dietary Approaches to Stop Hypertension (DASH)" was reported in 1997 by the National, Heart, Lung and Blood Institute of the National Institutes of Health. It investigated the effect of various eating patterns on lowering blood pressure. The DASH study was a multi-center research trial where food was provided to over 450 adults. It examined the effects of three different diets on high blood pressure: a control, "typical American" diet and two modified diets (high fruits-and-vegetables and a combination "DASH" diet - high in fruits, vegetables, and low fat dairy). See the table for a comparison of some of the components of the three diets.

Table: Comparison of the Three Diets Tested in the "DASH" Study

Of the three diets tested, the combination "DASH" diet resulted in the greatest decrease in blood pressure. Thus, this finding from a large and carefully executed clinical trial helped demonstrate that the combination "DASH" diet, with increased calcium, decreased blood pressure. A number of further studies have been done, all showing a similar relationship between increasing calcium intakes and decreased blood pressure. A study conducted after the original "DASH" study, referred to as the "DASH-Sodium" study showed that the DASH diet without sodium restriction provided as much blood pressure reduction as did severe sodium restriction on the control diet (1500 mg sodium/day). Overall it appears that consuming an adequate intake of fruits and vegetables as well as calcium from low fat dairy products plays a significant role in controlling blood pressure. Additional information and sample DASH menu plans are available on the National Heart, Lung and Blood Institute's Web site (http://www.nhlbi.nih.gov/health/public/heart/hbp/dash/index.htm).