TORONTO - Red wine has been touted as beneficial for cardiovascular health, but new research suggests that while one glass of that favourite Merlot or Shiraz may indeed be heart healthy, two or more could actually do more harm than good over time.
Furthermore, those good and bad effects on the heart and blood vessels aren't restricted just to red wine, but also apply to any kind of alcoholic drink, says principal investigator Dr. John Floras, director of cardiology research at the Peter Munk Cardiac Centre in Toronto.
Several large population studies have suggested light or moderate alcohol drinking has a protective effect on the heart; red wine, which contains antioxidant polyphenols, is thought to have particular benefits.
These studies found lower rates of heart disease, despite high-fat diets, among some European populations that regularly consume red wine. Widely known as the "French paradox," the phenomenon has created huge interest in how the libation might stave off cardiovascular disease.
In the Toronto study, Floras said tests on volunteers showed that drinking a single glass of red wine or an amount of ethanol (pure alcohol) equal to that found in a beer or a serving of spirits did indeed have potentially helpful effects on the heart and blood vessels.
"One standard drink of both the red wine and the alcohol causes the blood vessels to dilate (widen), which could be considered a good thing," he said. "It would make it easier for blood to flow through the vessels and reduce the work of the heart."
"But what happened after two drinks is the nervous system got turned on. And when the nervous system got turned on, that led to an increase in the impulses going to the blood vessels, which acted as a brake on further blood vessel dilation."
Floras said after two drinks, subjects' heart rates rose and their hearts began pumping more blood than necessary.
"So it suggests that there may be a physiological underpinning to this relationship in populations where one drink a day seems to be more beneficial than two drinks a day. And it may be that over time, revving up the nervous system, increasing the heart rate, increasing the pumping action of the heart may be part of the reason heavy drinking has been shown to have adverse effects."
Dr. George Fodor, head of research for the University of Ottawa Heart Institute's Minto Prevention and Rehabilitation Centre, said the findings provide a solid challenge to "the nonsensical statement that the French have low levels of heart disease because they drink red wine."
"The bottom line is if there is any benefit in alcohol, the range is very narrow," Fodor said Tuesday from Ottawa, commenting on the research. "So this study, I think, is a warning against trying to justify the drinking of alcohol for alleged health benefits."
Toronto cardiologist Beth Abramson, a spokeswoman for the Heart and Stroke Foundation, said that although the study looked at only a small number of subjects, it is important because it gives insights into how the heart, blood vessels and body react when exposed to alcohol.
"This is another piece of evidence - and it's done very elegantly - that suggests that just because a small amount of alcohol may be beneficial, more of it can actually be harmful," said Abramson, who was not involved in the study.
"Although it is enticing to think that alcohol would be a quick fix ... it actually isn't."
To conduct the study, published in the February issue of the American Journal of Physiology: Heart and Circulatory Physiology, researchers enrolled 13 healthy, non-smoking adults who were not heavy drinkers or total abstainers.
Participants attended three separate morning sessions, two weeks apart, during which "standard" drinks of red wine, ethanol or water were randomly administered. A 120-millilitre glass of wine and a 44-millilitre shot of spirits is considered a standard drink. The study used a moderately priced pinot noir with a high polyphenol content.
While agreeing the study is small, Floras said it is unique because it compares three different drinks - water, ethanol and red wine - in the same individuals on separate occasions, looking at different doses.
And because his lab contains a variety of testing methods, the researchers were able to simultaneously measure heart rate, blood pressure, blood vessel diameter and electrical impulses sent from the brain to the heart and the rest of the circulatory system.
"It would appear that following two or more drinks, the alcohol seems to turn on systems that do stress the circulation," he said.
"And our concern is if these stressful actions are repeated on a daily basis in individuals who have high alcohol consumption, they ultimately may be at higher risk of a heart attack or stroke or high blood pressure because of this potential mechanism."
