FRIDAY, Sept. 23 (HealthDay News) -- Many studies have shown that a glass or two of red wine a day is heart-healthy, and much of the benefit has been attributed to the anti-hypertensive effects of antioxidants found in red wine called polyphenols.

But a new Dutch study suggests that these polyphenols, at least in isolation, may not lower blood pressure after all.

Study author Ilse Botden, a graduate student at University Medical Center in Rotterdam, said the new findings "do not support" a lowering of blood pressure by polyphenols as the source of red wine's benefits to the cardiovascular system.

The findings are slated to be presented Friday at the American Heart Association's High Blood Pressure Research meeting in Orlando, Fla.

The new research involved 61 people averaging about 61 years of age, all of whom had borderline high blood pressure. Participants were given dairy beverages that contained either the red wine polyphenols or a harmless placebo.

Botden's team found no difference in blood pressure levels between the two groups after four weeks on the regimen.

"Red wine drinking may still be beneficial to prevent cardiovascular diseases. However, this apparently occurs in a blood pressure-independent manner," Botden said.

Dr. William O'Neill, a professor of cardiology and the executive dean for clinical affairs at the University of Miami Miller School of Medicine, agreed that the findings do not mean that red wine, in moderation, isn't heart-healthy.

"We know that moderate consumption of red wine helps decrease a person's risk for heart disease and heart attack," said O'Neill, who was not involved in the study.

Instead, this research seems to say that wine does not decrease heart risk through the mechanism of lowering blood pressure. Instead, red wine may have anti-inflammatory properties that lower cardiovascular risk, he said.

Another theory is that something in red wine help decreases the "stickiness" of blood and decreases the risk of a blood clot that could cause a heart attack, O'Neill said.

"We always want to get out a magic potion, and put it in pill form, but this study shows us that it's more complicated," he said.

Dr. Suzanne Steinbaum is a preventive cardiologist at Lenox Hill Hospital in New York City. She noted that the people in the study had borderline high blood pressure, and the results may not apply to people with higher blood pressure levels. The study also only lasted a month, she said, and the benefits from polyphenols might take longer to accrue.

"There are multiple components in red wine and taken together, these ingredients have been shown to decrease blood pressure and prevent clotting and heart attacks," Steinbaum said. Moderate consumption of red wine is also part of the Mediterranean diet or lifestyle, which is rich in fruits, vegetables, whole grains and lean proteins. "This lifestyle is good for heart health," she said.

Research presented at medical meetings should be considered preliminary until published in a peer-reviewed medical journal.

More information

There's more on high blood pressure at the U.S. National Heart, Lung, and Blood Institute.