Compound in soy products may help lower blood pressure

"What's unique about this study is that the results are very applicable to the general population. Our results strongly suggest a blood pressure benefit for moderate amounts of dietary isoflavone intake in young black and white adults," said Safiya Richardson, a graduating medical student at Columbia University's College of Physicians and Surgeons and the study's lead investigator. "Our study is the first to show a benefit in African Americans, who have a higher incidence of high blood pressure, with an earlier onset and more severe end-organ damage."

Compared to those consuming less than 0.33 mg of isoflavones per day, those reporting the most isoflavone intake (more than 2.5 mg per day) had a significantly lower systolic blood pressure (-5.5 mmHg lower on average). To help put this into context, an 8 ounce glass of soy milk has about 22 mg of isoflavones, and 100 g of roasted soybeans have as much as 130 mg.

"This could mean that consuming soy protein, for example, in combination with a DASH diet -- one that is high in fruits and vegetables, low-fat dairy and whole grains -- could lead to as much as a 10 mmHg drop in systolic blood pressure for pre-hypertensives, greatly improving their chances of not progressing to hypertension," said Richardson. "Any dietary or lifestyle modification people can easily make that doesn't require a daily medication is exciting, especially considering recent figures estimating that only about one third of American hypertensives have their blood pressure under control."

Isoflavones are thought to work by increasing the production of enzymes that create nitric oxide (NO), a substance that helps to dilate or widen blood vessels, thereby reducing the pressure created by blood against the vessel walls. Richardson said this mechanism may partially explain why the study was able to find an association with smaller amounts of isoflavone intake than examined previously. The relatively pronounced results in the overall biracial cohort may be driven by a more intense effect of isoflavones in African Americans, Richardson said. This is because endothelial dysfunction, a condition in which the blood vessels have a hard time either producing or using NO, plays a bigger role in hypertension in African Americans than it does in whites.

"It's possible that these foods may help compensate for this," she said. "Based on our results and those of previous studies, we would encourage the average adult to consider including moderate amounts of soy products in a healthy, well-balanced diet to reduce the chances of developing high blood pressure. For people with hypertension, it's important that they talk with their doctor about isoflavones as a possible addition to a low sodium DASH diet that could reduce the need for medication."

Richardson added that different soy products have different concentrations of isoflavones, so it is important for consumers to do their homework.

Researchers analyzed data from year-20 of the Coronary Artery Risk Development in Young Adults (CARDIA) study, which is an NIH-funded study created to examine the development and determinants of cardiovascular disease. This study began in 1985 with 5,115 African American and white Americans aged 18-30 years old who have been followed and reexamined at various intervals. Year-20 was the first year that participants completed an extensive dietary survey. Multivariable linear regression models evaluated the relation between daily isoflavone intake and systolic BP (SBP) after dividing patients across quartiles according to self-reported isoflavone intake. Even after controlling for age, sex, BMI, smoking, alcohol, physical activity and total caloric intake, the relationship between daily isoflavones and lower systolic blood pressure remained.

Richardson says this study helps lay the groundwork for randomized controlled trials to help better understand the association between isoflavones and blood pressure.

Richardson presented the study "Dietary Isoflavone Intake is Associated with Lower Systolic Blood Pressure: the Coronary Artery Risk Development in Young Adults (CARDIA) Study" on March 25, 2012 in McCormick Place South, Hall A.