Whether it's red wine or another spirit, the heart and blood vessels benefit slightly from one drink, but a second erases the positive effects, say Canadian researchers.
A study, published in the American Journal of Physiology, Heart and Circulatory Physiology, also raises more questions about the popular notion that red wine may be more effective against heart disease than other types of alcohol.
"We had anticipated that many of the effects of one ethanol drink would be enhanced by red wine. What was most surprising was how similar the effects were of red wine and ethanol. Any benefits that we found were not specific to red wine," said John Floras, MD, director of cardiology research at the Peter Munk Cardiac Centre at Toronto General Hospital.
Several population studies have shown light or moderate alcohol drinking may lower the risk of death and the development of heart disease. Many studies have also reported specific benefits of red wine.
The "French paradox," in which studies have found lower rates of heart disease, despite high-fat diets, in some European countries where red wine was consumed regularly, has also spurred interest in exploring whether red wine has special protective properties.
Researchers at the Canadian center conducted a real-time study of 13 volunteers who were given either 4 ounces of red wine, 15 ounces of ethanol or water at random at three separate sessions over two weeks. The volunteers were healthy, nonsmoking adults who were neither heavy drinkers nor total alcohol abstainers.
The wine, a moderately priced pinot noir, contained a high t-resveratrol content, a polyphenol compound found in plants, including red grapes, that exhibits antioxidant properties. Alcohol or substances in alcohol such as resveratrol may improve blood vessel function and also prevent platelets in the blood from sticking together, thus reducing clot formation and the risk of heart attack or stroke.
After one drink of either red wine or alcohol, blood vessels in the participant were more dilated, reducing the work the heart had to do. However, after two drinks, the heart rate, amount of blood pumped out of the heart, and action of the sympathetic nervous system (the part of the nervous system that is active during stress and is involved in regulating pulse and blood pressure) all increased. The ability of the blood vessels to expand in response to an increase in blood flow also diminished.
Increases in heart rate and sympathetic nervous system activity are recognized markers for hypertension, heart failure and sudden death.
Dr. Floras cautioned that this study measured the effects of these drinks on one occasion only. The effects of daily wine or alcohol intake may be quite different.
"Our findings point to a slight beneficial effect of one drink—be it alcohol or red wine—on the heart and blood vessels, whereas two or more drinks would seem to turn on systems that stress the circulation. If these actions are repeated frequently because of high alcohol consumption, these effects may expose individuals to a higher risk of heart attacks, stroke or chronic high blood pressure," Dr. Floras said.
The American Heart Association does not recommend that anyone start drinking alcohol to prevent heart disease. Reducing risk can be done using other methods such as exercise and following a healthy diet.